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9.2. Funkcijų sąrašas

QGIS prieinamos funkcijos, operatoriai ir kintamieji išvardinti žemiau, sugrupuoti pagal kategorijas.

9.2.1. Agregavimo funkcijos

Šioje grupėje yra funkcijos, kurios agreguoja sluoksnių ir laukų reikšmes.

9.2.1.1. aggregate

Grąžina agreguotą reikšmę, paskaičiuotą naudojant kito sluoksnio geoobjektus.

Sintaksė

aggregate(layer, aggregate, expression, [filter], [concatenator=‘‘], [order_by])

[] žymi neprivalomus argumentus

Argumentai

  • layer - tekstas, reprezentuojantis arba sluoksnio pavadinimą, arba sluoksnio ID

  • aggregate - tekstas, nurodantis, kokį skaičiuoti agregatą. Galimos parinktys yra:

    • count

    • count_distinct

    • count_missing

    • minimum ar min

    • maximum ar max

    • sum

    • mean

    • median

    • stdev

    • stdevsample

    • range

    • minority

    • majority

    • q1: pirmas kvartilis

    • q3: trečias kvartilis

    • iqr: tarpkvartilinis diapazonas

    • min_length: minimalus teksto ilgis

    • max_length: maksimalus teksto ilgis

    • concatenate: sujungti tekstus jungtuku

    • concatenate_unique: sujungti unikalius tekstus jungtuku

    • collect: kurti agreguotą kelių dalių geometriją

    • array_agg: kurti agreguotų reikšmių masyvą

  • expression - vidinė išraiška arba lauko pavadinimas agregavimui

  • filter - neprivaloma filtro išraiška, ribojanti agregato skaičiavimui naudojamus geoobjektus. Laukai ir geometrijos yra iš susieto sluoksnio geoobjektų. Šaltinio geoobjektą galima pasiekti kintamuoju @parent.

  • concatenator - neprivalomas tekstas, kuris naudojamas jungiant reikšmes, kai vykdomi „concatenate“ ir „concatenate_unique“ agregatai

  • order_by - neprivaloma filtro išraiška agregato skaičiavimo geoobjektų rikiavimui. Laukai ir geometrija yra iš susiejamo sluoksnio geoobjektų. Pagal nutylėjimą geoobjektai grąžinami atsitiktine tvarka.

Pavyzdžiai

  • aggregate(layer:='stotys',aggregate:='sum',expression:="keleiviai") → visų sluoksnio stotys lauko keleiviai reikšmių suma

  • aggregate('stotys','sum', "keleiviai"/7) → skaičiuoja „keleiviai“ dienos vidurkį, dalinant lauko „keleiviai“ reikšmę iš 7, prieš susumuojant reikšmes

  • aggregate(layer:='stotys',aggregate:='sum',expression:="keleiviai",filter:="klase">3) → sumuoja lauko „keleiviai“ reikšmes tik iš geoobjektų, kurių atribotas „klase“ yra didesnis už 3

  • aggregate(layer:='stotys',aggregate:='concatenate', expression:="pavadinimas", concatenator:=',') → sąrašas visų sluoksnio stotys geoobjektų pavadinimų, atskirtų kableliais

  • aggregate(layer:='salys', aggregate:='max', expression:="kodas", filter:=intersects( @geometry, geometry(@parent) ) ) → Sluoksnio „salys“ laukas „kodas“ iš susikertančios šalies

  • aggregate(layer:='stotys',aggregate:='sum',expression:="keleiviai",filter:=contains( @atlas_geometry, @geometry ) ) → suma visų sluoksnio „stotys“ lauko „keleiviai“ reikšmių, esančių dabartiniame atlaso geoobjekte

  • aggregate(layer:='stotys', aggregate:='collect', expression:=centroid(@geometry), filter:="regionas" = attribute(@parent,'name') ) → agreguoja visas stočių geometrijas, esančias tame pačiame regione, kaip ir dabartinis geoobjektas

9.2.1.2. array_agg

Grąžina lauko ar išraiškos reikšmių agreguotą masyvą.

Sintaksė

array_agg(expression, [group_by], [filter], [order_by])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

  • order_by - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų rikiavimui. Pagal nutylėjimą geoobjektai grąžinami atsitiktine tvarka.

Pavyzdžiai

  • array_agg("pavadinimas",group_by:="busena") → sąrašas pavadinimo reikšmių, sugrupuotas pagal būsenos lauką

9.2.1.3. collect

Returns the multipart geometry of aggregated geometries from an expression

Sintaksė

collect(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - geometry expression to aggregate

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • collect( @geometry ) → multipart geometry of aggregated geometries

  • collect( centroid(@geometry), group_by:="region", filter:= "use" = 'civilian' ) → aggregated centroids of the civilian features based on their region value

9.2.1.4. concatenate

Returns all aggregated strings from a field or expression joined by a delimiter.

Sintaksė

concatenate(expression, [group_by], [filter], [concatenator], [order_by])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

  • concatenator - optional string to use to join values. Empty by default.

  • order_by - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų rikiavimui. Pagal nutylėjimą geoobjektai grąžinami atsitiktine tvarka.

Pavyzdžiai

  • concatenate("town_name",group_by:="state",concatenator:=',') → comma separated list of town_names, grouped by state field

9.2.1.5. concatenate_unique

Returns all unique strings from a field or expression joined by a delimiter.

Sintaksė

concatenate_unique(expression, [group_by], [filter], [concatenator], [order_by])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

  • concatenator - optional string to use to join values. Empty by default.

  • order_by - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų rikiavimui. Pagal nutylėjimą geoobjektai grąžinami atsitiktine tvarka.

Pavyzdžiai

  • concatenate_unique("town_name",group_by:="state",concatenator:=',') → comma separated list of unique town_names, grouped by state field

9.2.1.6. count

Returns the count of matching features.

Sintaksė

count(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • count("stations",group_by:="state") → count of stations, grouped by state field

9.2.1.7. count_distinct

Returns the count of distinct values.

Sintaksė

count_distinct(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • count_distinct("stations",group_by:="state") → count of distinct stations values, grouped by state field

9.2.1.8. count_missing

Returns the count of missing (NULL) values.

Sintaksė

count_missing(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • count_missing("stations",group_by:="state") → count of missing (NULL) station values, grouped by state field

9.2.1.9. iqr

Returns the calculated inter quartile range from a field or expression.

Sintaksė

iqr(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • iqr("population",group_by:="state") → inter quartile range of population value, grouped by state field

9.2.1.10. majority

Returns the aggregate majority of values (most commonly occurring value) from a field or expression.

Sintaksė

majority(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • majority("class",group_by:="state") → most commonly occurring class value, grouped by state field

9.2.1.11. max_length

Returns the maximum length of strings from a field or expression.

Sintaksė

max_length(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • max_length("town_name",group_by:="state") → maximum length of town_name, grouped by state field

9.2.1.12. maximum

Returns the aggregate maximum value from a field or expression.

Sintaksė

maximum(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • maximum("population",group_by:="state") → maximum population value, grouped by state field

9.2.1.13. mean

Returns the aggregate mean value from a field or expression.

Sintaksė

mean(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • mean("population",group_by:="state") → mean population value, grouped by state field

9.2.1.14. median

Returns the aggregate median value from a field or expression.

Sintaksė

median(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • median("population",group_by:="state") → median population value, grouped by state field

9.2.1.15. min_length

Returns the minimum length of strings from a field or expression.

Sintaksė

min_length(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • min_length("town_name",group_by:="state") → minimum length of town_name, grouped by state field

9.2.1.16. minimum

Returns the aggregate minimum value from a field or expression.

Sintaksė

minimum(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • minimum("population",group_by:="state") → minimum population value, grouped by state field

9.2.1.17. minority

Returns the aggregate minority of values (least occurring value) from a field or expression.

Sintaksė

minority(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • minority("class",group_by:="state") → least occurring class value, grouped by state field

9.2.1.18. q1

Returns the calculated first quartile from a field or expression.

Sintaksė

q1(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • q1("population",group_by:="state") → first quartile of population value, grouped by state field

9.2.1.19. q3

Returns the calculated third quartile from a field or expression.

Sintaksė

q3(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • q3("population",group_by:="state") → third quartile of population value, grouped by state field

9.2.1.20. range

Returns the aggregate range of values (maximum - minimum) from a field or expression.

Sintaksė

range(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • range("population",group_by:="state") → range of population values, grouped by state field

9.2.1.21. relation_aggregate

Returns an aggregate value calculated using all matching child features from a layer relation.

Sintaksė

relation_aggregate(relation, aggregate, expression, [concatenator=‘‘], [order_by])

[] žymi neprivalomus argumentus

Argumentai

  • relation - a string, representing a relation ID

  • aggregate - tekstas, nurodantis, kokį skaičiuoti agregatą. Galimos parinktys yra:

    • count

    • count_distinct

    • count_missing

    • minimum ar min

    • maximum ar max

    • sum

    • mean

    • median

    • stdev

    • stdevsample

    • range

    • minority

    • majority

    • q1: pirmas kvartilis

    • q3: trečias kvartilis

    • iqr: tarpkvartilinis diapazonas

    • min_length: minimalus teksto ilgis

    • max_length: maksimalus teksto ilgis

    • concatenate: sujungti tekstus jungtuku

    • concatenate_unique: sujungti unikalius tekstus jungtuku

    • collect: kurti agreguotą kelių dalių geometriją

    • array_agg: kurti agreguotų reikšmių masyvą

  • expression - vidinė išraiška arba lauko pavadinimas agregavimui

  • concatenator - optional string to use to join values for ‚concatenate‘ aggregate

  • order_by - optional expression to order the features used for calculating the aggregate. Fields and geometry are from the features on the joined layer. By default, the features will be returned in an unspecified order.

Pavyzdžiai

  • relation_aggregate(relation:='my_relation',aggregate:='mean',expression:="passengers") → mean value of all matching child features using the ‚my_relation‘ relation

  • relation_aggregate('my_relation','sum', "passengers"/7) → sum of the passengers field divided by 7 for all matching child features using the ‚my_relation‘ relation

  • relation_aggregate('my_relation','concatenate', "towns", concatenator:=',') → comma separated list of the towns field for all matching child features using the ‚my_relation‘ relation

  • relation_aggregate('my_relation','array_agg', "id") → array of the id field from all matching child features using the ‚my_relation‘ relation

Further reading: Setting relations between multiple layers

9.2.1.22. stdev

Returns the aggregate standard deviation value from a field or expression.

Sintaksė

stdev(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • stdev("population",group_by:="state") → standard deviation of population value, grouped by state field

9.2.1.23. sum

Returns the aggregate summed value from a field or expression.

Sintaksė

sum(expression, [group_by], [filter])

[] žymi neprivalomus argumentus

Argumentai

  • expression - agreguojamo lauko subišraiška

  • group_by - neprivaloma išraiška, kuri naudojama agregatų grupavimui

  • filter - neprivaloma išraiška, kuri naudojama skaičiuojamo agregato geoobjektų filtravimui

Pavyzdžiai

  • sum("population",group_by:="state") → summed population value, grouped by state field

9.2.2. Array Functions

This group contains functions to create and manipulate arrays (also known as list data structures). The order of values within the array matters, unlike the ‚map‘ data structure, where the order of key-value pairs is irrelevant and values are identified by their keys.

9.2.2.1. array

Returns an array containing all the values passed as parameter.

Sintaksė

array(value1, value2, …)

Argumentai

  • value - a value

Pavyzdžiai

  • array(2,10) → [ 2, 10 ]

  • array(2,10)[0] → 2

9.2.2.2. array_all

Returns TRUE if an array contains all the values of a given array.

Sintaksė

array_all(array_a, array_b)

Argumentai

  • array_a - an array

  • array_b - the array of values to search

Pavyzdžiai

  • array_all(array(1,2,3),array(2,3)) → TRUE

  • array_all(array(1,2,3),array(1,2,4)) → FALSE

9.2.2.3. array_append

Returns an array with the given value added at the end.

Sintaksė

array_append(array, value)

Argumentai

  • array - an array

  • value - the value to add

Pavyzdžiai

  • array_append(array(1,2,3),4) → [ 1, 2, 3, 4 ]

9.2.2.4. array_cat

Returns an array containing all the given arrays concatenated.

Sintaksė

array_cat(array1, array2, …)

Argumentai

  • array - an array

Pavyzdžiai

  • array_cat(array(1,2),array(2,3)) → [ 1, 2, 2, 3 ]

9.2.2.5. array_contains

Returns TRUE if an array contains the given value.

Sintaksė

array_contains(array, value)

Argumentai

  • array - an array

  • value - the value to search

Pavyzdžiai

  • array_contains(array(1,2,3),2) → TRUE

9.2.2.6. array_count

Counts the number of occurrences of a given value in an array.

Sintaksė

array_count(array, value)

Argumentai

  • array - an array

  • value - the value to count

Pavyzdžiai

  • array_count(array('a', 'b', 'c', 'b'), 'b') → 2

9.2.2.7. array_distinct

Returns an array containing distinct values of the given array.

Sintaksė

array_distinct(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_distinct(array(1,2,3,2,1)) → [ 1, 2, 3 ]

9.2.2.8. array_filter

Returns an array with only the items for which the expression evaluates to true.

Sintaksė

array_filter(array, expression, [limit=0])

[] žymi neprivalomus argumentus

Argumentai

  • array - an array

  • expression - an expression to evaluate on each item. The variable @element will be replaced by the current value.

  • limit - maximum number of elements to be returned. Use 0 to return all values.

Pavyzdžiai

  • array_filter(array(1,2,3),@element < 3) → [ 1, 2 ]

  • array_filter(array(1,2,3),@element < 3, 1) → [ 1 ]

9.2.2.9. array_find

Returns the lowest index (0 for the first one) of a value within an array. Returns -1 if the value is not found.

Sintaksė

array_find(array, value)

Argumentai

  • array - an array

  • value - the value to search

Pavyzdžiai

  • array_find(array('a', 'b', 'c'), 'b') → 1

  • array_find(array('a', 'b', 'c', 'b'), 'b') → 1

9.2.2.10. array_first

Returns the first value of an array.

Sintaksė

array_first(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_first(array('a','b','c')) → ‚a‘

9.2.2.11. array_foreach

Returns an array with the given expression evaluated on each item.

Sintaksė

array_foreach(array, expression)

Argumentai

  • array - an array

  • expression - an expression to evaluate on each item. The variable @element will be replaced by the current value and the variable @counter by the current index (starting with 0).

Pavyzdžiai

  • array_foreach(array('a','b','c'),upper(@element)) → [ ‚A‘, ‚B‘, ‚C‘ ]

  • array_foreach(array(1,2,3),@element + 10) → [ 11, 12, 13 ]

  • array_foreach(array(1,2,3),@element + @counter) → [ 1, 3, 5 ]

9.2.2.12. array_get

Returns the Nth value (0 for the first one) or the last -Nth value (-1 for the last one) of an array.

Sintaksė

array_get(array, pos)

Argumentai

  • array - an array

  • pos - the index to get (0 based)

Pavyzdžiai

  • array_get(array('a','b','c'),1) → ‚b‘

  • array_get(array('a','b','c'),-1) → ‚c‘

Patarimas

You can also use the index operator ([]) to get a value from an array.

9.2.2.13. array_insert

Returns an array with the given value added at the given position.

Sintaksė

array_insert(array, pos, value)

Argumentai

  • array - an array

  • pos - the position where to add (0 based)

  • value - the value to add

Pavyzdžiai

  • array_insert(array(1,2,3),1,100) → [ 1, 100, 2, 3 ]

9.2.2.14. array_intersect

Returns TRUE if at least one element of array1 exists in array2.

Sintaksė

array_intersect(array1, array2)

Argumentai

  • array1 - an array

  • array2 - another array

Pavyzdžiai

  • array_intersect(array(1,2,3,4),array(4,0,2,5)) → TRUE

9.2.2.15. array_last

Returns the last value of an array.

Sintaksė

array_last(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_last(array('a','b','c')) → ‚c‘

9.2.2.16. array_length

Returns the number of elements of an array.

Sintaksė

array_length(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_length(array(1,2,3)) → 3

9.2.2.17. array_majority

Returns the most common values in an array.

Sintaksė

array_majority(array, [option=‘all‘])

[] žymi neprivalomus argumentus

Argumentai

  • array - an array

  • option=‘all‘ - a string specifying the return values handling. Valid options are:

    • all: Default, all most common values are returned in an array.

    • any: Returns one of the most common values.

    • median: Returns the median of the most common values. Non arithmetic values are ignored.

    • real_majority: Returns the value which occurs more than half the size of the array.

Pavyzdžiai

  • array_majority(array(0,1,42,42,43), 'all') → [ 42 ]

  • array_majority(array(0,1,42,42,43,1), 'all') → [ 42, 1 ]

  • array_majority(array(0,1,42,42,43,1), 'any') → 1 or 42

  • array_majority(array(0,1,1,2,2), 'median') → 1.5

  • array_majority(array(0,1,42,42,43), 'real_majority') → NULL

  • array_majority(array(0,1,42,42,43,42), 'real_majority') → NULL

  • array_majority(array(0,1,42,42,43,42,42), 'real_majority') → 42

9.2.2.18. array_max

Returns the maximum value of an array.

Sintaksė

array_max(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_max(array(0,42,4,2)) → 42

9.2.2.19. array_mean

Returns the mean of arithmetic values in an array. Non numeric values in the array are ignored.

Sintaksė

array_mean(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_mean(array(0,1,7,66.6,135.4)) → 42

  • array_mean(array(0,84,'a','b','c')) → 42

9.2.2.20. array_median

Returns the median of arithmetic values in an array. Non arithmetic values in the array are ignored.

Sintaksė

array_median(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_median(array(0,1,42,42,43)) → 42

  • array_median(array(0,1,2,42,'a','b')) → 1.5

9.2.2.21. array_min

Returns the minimum value of an array.

Sintaksė

array_min(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_min(array(43,42,54)) → 42

9.2.2.22. array_minority

Returns the less common values in an array.

Sintaksė

array_minority(array, [option=‘all‘])

[] žymi neprivalomus argumentus

Argumentai

  • array - an array

  • option=‘all‘ - a string specifying the return values handling. Valid options are:

    • all: Default, all less common values are returned in an array.

    • any: Returns one of the less common values.

    • median: Returns the median of the less common values. Non arithmetic values are ignored.

    • real_minority: Returns values which occur less than half the size of the array.

Pavyzdžiai

  • array_minority(array(0,42,42), 'all') → [ 0 ]

  • array_minority(array(0,1,42,42), 'all') → [ 0, 1 ]

  • array_minority(array(0,1,42,42,43,1), 'any') → 0 or 43

  • array_minority(array(1,2,3,3), 'median') → 1.5

  • array_minority(array(0,1,42,42,43), 'real_minority') → [ 42, 43, 0, 1 ]

  • array_minority(array(0,1,42,42,43,42), 'real_minority') → [ 42, 43, 0, 1 ]

  • array_minority(array(0,1,42,42,43,42,42), 'real_minority') → [ 43, 0, 1 ]

9.2.2.23. array_prepend

Returns an array with the given value added at the beginning.

Sintaksė

array_prepend(array, value)

Argumentai

  • array - an array

  • value - the value to add

Pavyzdžiai

  • array_prepend(array(1,2,3),0) → [ 0, 1, 2, 3 ]

9.2.2.24. array_prioritize

Returns an array sorted using the ordering specified in another array. Values which are present in the first array but are missing from the second array will be added to the end of the result.

Sintaksė

array_prioritize(array, array_prioritize)

Argumentai

  • array - an array

  • array_prioritize - an array with values ordered by priority

Pavyzdžiai

  • array_prioritize(array(1, 8, 2, 5), array(5, 4, 2, 1, 3, 8)) → [ 5, 2, 1, 8 ]

  • array_prioritize(array(5, 4, 2, 1, 3, 8), array(1, 8, 6, 5)) → [ 1, 8, 5, 4, 2, 3 ]

9.2.2.25. array_remove_all

Returns an array with all the entries of the given value removed.

Sintaksė

array_remove_all(array, value)

Argumentai

  • array - an array

  • value - the values to remove

Pavyzdžiai

  • array_remove_all(array('a','b','c','b'),'b') → [ ‚a‘, ‚c‘ ]

9.2.2.26. array_remove_at

Returns an array with the item at the given index removed. Supports positive (0 for the first element) and negative (the last -Nth value, -1 for the last element) index.

Sintaksė

array_remove_at(array, pos)

Argumentai

  • array - an array

  • pos - the position to remove (0 based)

Pavyzdžiai

  • array_remove_at(array(1, 2, 3), 1) → [1, 3 ]

  • array_remove_at(array(1, 2, 3), -1) → [1, 2 ]

9.2.2.27. array_replace

Returns an array with the supplied value, array, or map of values replaced.

Value & array variant

Returns an array with the supplied value or array of values replaced by another value or an array of values.

Sintaksė

array_replace(array, before, after)

Argumentai

  • array - the input array

  • before - the value or array of values to replace

  • after - the value or array of values to use as a replacement

Pavyzdžiai

  • array_replace(array('QGIS','SHOULD','ROCK'),'SHOULD','DOES') → [ ‚QGIS‘, ‚DOES‘, ‚ROCK‘ ]

  • array_replace(array(3,2,1),array(1,2,3),array(7,8,9)) → [ 9, 8, 7 ]

  • array_replace(array('Q','G','I','S'),array('Q','S'),'-') → [ ‚-‘, ‚G‘, ‚I‘, ‚-‘ ]

Map variant

Returns an array with the supplied map keys replaced by their paired values.

Sintaksė

array_replace(array, map)

Argumentai

  • array - the input array

  • map - the map containing keys and values

Pavyzdžiai

  • array_replace(array('APP', 'SHOULD', 'ROCK'),map('APP','QGIS','SHOULD','DOES')) → [ ‚QGIS‘, ‚DOES‘, ‚ROCK‘ ]

Further reading: replace, regexp_replace

9.2.2.28. array_reverse

Returns the given array with array values in reversed order.

Sintaksė

array_reverse(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_reverse(array(2,4,0,10)) → [ 10, 0, 4, 2 ]

9.2.2.29. array_slice

Returns a portion of the array. The slice is defined by the start_pos and end_pos arguments.

Sintaksė

array_slice(array, start_pos, end_pos)

Argumentai

  • array - an array

  • start_pos - the index of the start position of the slice (0 based). The start_pos index is included in the slice. If you use a negative start_pos, the index is counted from the end of the list (-1 based).

  • end_pos - the index of the end position of the slice (0 based). The end_pos index is included in the slice. If you use a negative end_pos, the index is counted from the end of the list (-1 based).

Pavyzdžiai

  • array_slice(array(1,2,3,4,5),0,3) → [ 1, 2, 3, 4 ]

  • array_slice(array(1,2,3,4,5),0,-1) → [ 1, 2, 3, 4, 5 ]

  • array_slice(array(1,2,3,4,5),-5,-1) → [ 1, 2, 3, 4, 5 ]

  • array_slice(array(1,2,3,4,5),0,0) → [ 1 ]

  • array_slice(array(1,2,3,4,5),-2,-1) → [ 4, 5 ]

  • array_slice(array(1,2,3,4,5),-1,-1) → [ 5 ]

  • array_slice(array('Dufour','Valmiera','Chugiak','Brighton'),1,2) → [ ‚Valmiera‘, ‚Chugiak‘ ]

  • array_slice(array('Dufour','Valmiera','Chugiak','Brighton'),-2,-1) → [ ‚Chugiak‘, ‚Brighton‘ ]

9.2.2.30. array_sort

Returns the provided array with its elements sorted.

Sintaksė

array_sort(array, [ascending=true])

[] žymi neprivalomus argumentus

Argumentai

  • array - an array

  • ascending - set this parameter to false to sort the array in descending order

Pavyzdžiai

  • array_sort(array(3,2,1)) → [ 1, 2, 3 ]

9.2.2.31. array_sum

Returns the sum of arithmetic values in an array. Non numeric values in the array are ignored.

Sintaksė

array_sum(array)

Argumentai

  • array - an array

Pavyzdžiai

  • array_sum(array(0,1,39.4,1.6,'a')) → 42.0

9.2.2.32. array_to_string

Concatenates array elements into a string separated by a delimiter and using optional string for empty values.

Sintaksė

array_to_string(array, [delimiter=‘,‘], [empty_value=‘‘])

[] žymi neprivalomus argumentus

Argumentai

  • array - the input array

  • delimiter - the string delimiter used to separate concatenated array elements

  • empty_value - the optional string to use as replacement for empty (zero length) matches

Pavyzdžiai

  • array_to_string(array('1','2','3')) → ‚1,2,3‘

  • array_to_string(array(1,2,3),'-') → ‚1-2-3‘

  • array_to_string(array('1','','3'),',','0') → ‚1,0,3‘

Further reading: string_to_array

9.2.2.33. generate_series

Creates an array containing a sequence of numbers.

Sintaksė

generate_series(start, stop, [step=1])

[] žymi neprivalomus argumentus

Argumentai

  • start - first value of the sequence

  • stop - value that ends the sequence once reached

  • step - value used as the increment between values

Pavyzdžiai

  • generate_series(1,5) → [ 1, 2, 3, 4, 5 ]

  • generate_series(5,1,-1) → [ 5, 4, 3, 2, 1 ]

9.2.2.34. geometries_to_array

Splits a geometry into simpler geometries in an array.

Sintaksė

geometries_to_array(geometry)

Argumentai

  • geometry - the input geometry

Pavyzdžiai

  • geometries_to_array(geom_from_wkt('MultiPoint (1 2, 5 21)')) → An array containing ‚Point (1 2)‘ and ‚Point (5 21)‘

  • geometries_to_array(geom_from_wkt('GeometryCollection (Polygon ((5 8, 4 1, 3 2, 5 8)),LineString (3 2, 4 2))')) → an array of a polygon and a line geometries

  • geom_to_wkt(geometries_to_array(geom_from_wkt('GeometryCollection (Polygon ((5 8, 4 1, 3 2, 5 8)),LineString (3 2, 4 2))'))[0]) → ‚Polygon ((5 8, 4 1, 3 2, 5 8))‘

  • geometries_to_array(geom_from_wkt('MULTIPOLYGON(((5 5,0 0,0 10,5 5)),((5 5,10 10,10 0,5 5))')) → an array of two polygon geometries

9.2.2.35. regexp_matches

Returns an array of all strings captured by capturing groups, in the order the groups themselves appear in the supplied regular expression against a string.

Sintaksė

regexp_matches(string, regex, [empty_value=‘‘])

[] žymi neprivalomus argumentus

Argumentai

  • string - the string to capture groups from against the regular expression

  • regex - the regular expression used to capture groups

  • empty_value - the optional string to use as replacement for empty (zero length) matches

Pavyzdžiai

  • regexp_matches('QGIS=>rocks','(.*)=>(.*)') → [ ‚QGIS‘, ‚rocks‘ ]

  • regexp_matches('key=>','(.*)=>(.*)','empty value') → [ ‚key‘, ‚empty value‘ ]

Further reading: substr, regexp_substr

9.2.2.36. string_to_array

Splits string into an array using supplied delimiter and optional string for empty values.

Sintaksė

string_to_array(string, [delimiter=‘,‘], [empty_value=‘‘])

[] žymi neprivalomus argumentus

Argumentai

  • string - the input string

  • delimiter - the string delimiter used to split the input string

  • empty_value - the optional string to use as replacement for empty (zero length) matches

Pavyzdžiai

  • string_to_array('1,2,3',',') → [ ‚1‘, ‚2‘, ‚3‘ ]

  • string_to_array('1,,3',',','0') → [ ‚1‘, ‚0‘, ‚3‘ ]

Further reading: array_to_string

9.2.3. Color Functions

This group contains functions for manipulating colors.

9.2.3.1. color_cmyk

Returns a string representation of a color based on its cyan, magenta, yellow and black components

Sintaksė

color_cmyk(cyan, magenta, yellow, black)

Argumentai

  • cyan - cyan component of the color, as a percentage integer value from 0 to 100

  • magenta - magenta component of the color, as a percentage integer value from 0 to 100

  • yellow - yellow component of the color, as a percentage integer value from 0 to 100

  • black - black component of the color, as a percentage integer value from 0 to 100

Pavyzdžiai

  • color_cmyk(100,50,0,10) → ‚0,115,230‘

9.2.3.2. color_cmyka

Returns a string representation of a color based on its cyan, magenta, yellow, black and alpha (transparency) components

Sintaksė

color_cmyka(cyan, magenta, yellow, black, alpha)

Argumentai

  • cyan - cyan component of the color, as a percentage integer value from 0 to 100

  • magenta - magenta component of the color, as a percentage integer value from 0 to 100

  • yellow - yellow component of the color, as a percentage integer value from 0 to 100

  • black - black component of the color, as a percentage integer value from 0 to 100

  • alpha - alpha component as an integer value from 0 (completely transparent) to 255 (opaque).

Pavyzdžiai

  • color_cmyka(100,50,0,10,200) → ‚0,115,230,200‘

9.2.3.3. color_cmykf

Returns a color object based on its cyan, magenta, yellow, black and alpha components.

Sintaksė

color_cmykf(cyan, magenta, yellow, black, [alpha=1.0])

[] žymi neprivalomus argumentus

Argumentai

  • cyan - cyan component as a float value from 0.0 to 1.0

  • magenta - magenta component as a float value from 0.0 to 1.0

  • yellow - yellow component as a float value from 0.0 to 1.0

  • black - black component as a float value from 0.0 to 1.0

  • alpha - alpha component as a float value from 0.0 to 1.0

Pavyzdžiai

  • color_cmykf(1,0.9,0.81,0.62) → CMYKA: 1.00,0.90,0.81,0.62,1.00

9.2.3.4. color_grayscale_average

Applies a grayscale filter to a color and returns it. Returned type is the same as color argument, i.e. a color string representation or a color object.

Sintaksė

color_grayscale_average(color)

Argumentai

  • color - a color string representation or a color object

Pavyzdžiai

  • color_grayscale_average('255,100,50') → ‚135,135,135,255‘

  • color_grayscale_average(color_cmykf(0.6,0.5,0.1,0.8)) → CMYKA: 0.40,0.40,0.40,0.80,1.00

9.2.3.5. color_hsl

Returns a string representation of a color based on its hue, saturation, and lightness attributes.

Sintaksė

color_hsl(hue, saturation, lightness)

Argumentai

  • hue - hue of the color, as an integer value from 0 to 360

  • saturation - saturation percentage of the color as an integer value from 0 to 100

  • lightness - lightness percentage of the color as an integer value from 0 to 100

Pavyzdžiai

  • color_hsl(100,50,70) → ‚166,217,140‘

9.2.3.6. color_hsla

Returns a string representation of a color based on its hue, saturation, lightness and alpha (transparency) attributes

Sintaksė

color_hsla(hue, saturation, lightness, alpha)

Argumentai

  • hue - hue of the color, as an integer value from 0 to 360

  • saturation - saturation percentage of the color as an integer value from 0 to 100

  • lightness - lightness percentage of the color as an integer value from 0 to 100

  • alpha - alpha component as an integer value from 0 (completely transparent) to 255 (opaque).

Pavyzdžiai

  • color_hsla(100,50,70,200) → ‚166,217,140,200‘

9.2.3.7. color_hslf

Returns a color object based on its hue, saturation, and lightness attributes.

Sintaksė

color_hslf(hue, saturation, lightness, [alpha=1.0])

[] žymi neprivalomus argumentus

Argumentai

  • hue - hue of the color, as a float value from 0.0 to 1.0

  • saturation - saturation of the color as a float value from 0.0 to 1.0

  • lightness - lightness of the color as a float value from 0.0 to 1.0

  • alpha - alpha component as a float value from 0.0 to 1.0

Pavyzdžiai

  • color_hslf(0.3,0.52,0.7) → HSLA: 0.30,0.52,0.70,1.00

9.2.3.8. color_hsv

Returns a string representation of a color based on its hue, saturation, and value attributes.

Sintaksė

color_hsv(hue, saturation, value)

Argumentai

  • hue - hue of the color, as an integer value from 0 to 360

  • saturation - saturation percentage of the color as an integer value from 0 to 100

  • value - value percentage of the color as an integer from 0 to 100

Pavyzdžiai

  • color_hsv(40,100,100) → ‚255,170,0‘

9.2.3.9. color_hsva

Returns a string representation of a color based on its hue, saturation, value and alpha (transparency) attributes.

Sintaksė

color_hsva(hue, saturation, value, alpha)

Argumentai

  • hue - hue of the color, as an integer value from 0 to 360

  • saturation - saturation percentage of the color as an integer value from 0 to 100

  • value - value percentage of the color as an integer from 0 to 100

  • alpha - alpha component as an integer value from 0 (completely transparent) to 255 (opaque)

Pavyzdžiai

  • color_hsva(40,100,100,200) → ‚255,170,0,200‘

9.2.3.10. color_hsvf

Returns a color object based on its hue, saturation, and value attributes.

Sintaksė

color_hsvf(hue, saturation, value, [alpha=1.0])

[] žymi neprivalomus argumentus

Argumentai

  • hue - hue of the color, as a float value from 0.0 to 1.0

  • saturation - saturation of the color as a float value from 0.0 to 1.0

  • value - value of the color as as a float value from 0.0 to 1.0

  • alpha - alpha component as a float value from 0.0 to 1.0

Pavyzdžiai

  • color_hsvf(0.4,1,0.6) → HSVA: 0.40,1.00,0.60,1.00

9.2.3.11. color_mix

Returns a color mixing the red, green, blue, and alpha values of two provided colors based on a given ratio. Returned type is the same as color arguments, i.e. a color string representation or a color object.

Sintaksė

color_mix(color1, color2, ratio)

Argumentai

  • color1 - a color string or a color object

  • color2 - a color string or a color object

  • ratio - a ratio

Pavyzdžiai

  • color_mix_rgb('0,0,0','255,255,255',0.5) → ‚127,127,127,255‘

  • color_mix(color_cmykf(0.9,0.9,0.9,0.9),color_cmykf(0.1,0.1,0.1,0.1),0.5) → CMYKA: 0.50,0.50,0.50,0.50,1.00

9.2.3.12. color_mix_rgb

Returns a string representing a color mixing the red, green, blue, and alpha values of two provided colors based on a given ratio.

Sintaksė

color_mix_rgb(color1, color2, ratio)

Argumentai

  • color1 - a color string

  • color2 - a color string

  • ratio - a ratio

Pavyzdžiai

  • color_mix_rgb('0,0,0','255,255,255',0.5) → ‚127,127,127,255‘

9.2.3.13. color_part

Returns a specific component from a color string or color object, e.g., the red component or alpha component.

Sintaksė

color_part(color, component)

Argumentai

  • color - a color string or a color object

  • component - a string corresponding to the color component to return. Valid options are:

    • red: RGB red component (0-255)

    • green: RGB green component (0-255)

    • blue: RGB blue component (0-255)

    • alpha: alpha (transparency) value (0-255)

    • hue: HSV hue (0-360)

    • saturation: HSV saturation (0-100)

    • value: HSV value (0-100)

    • hsl_hue: HSL hue (0-360)

    • hsl_saturation: HSL saturation (0-100)

    • lightness: HSL lightness (0-100)

    • cyan: CMYK cyan component (0-100)

    • magenta: CMYK magenta component (0-100)

    • yellow: CMYK yellow component (0-100)

    • black: CMYK black component (0-100)

Pavyzdžiai

  • color_part('200,10,30','green') → 10

  • to_int(color_part(color_cmykf(0.1,0.2,0.3,0.9),'black')) → 90

9.2.3.14. color_rgb

Returns a string representation of a color based on its red, green, and blue components.

Sintaksė

color_rgb(red, green, blue)

Argumentai

  • red - red component as an integer value from 0 to 255

  • green - green component as an integer value from 0 to 255

  • blue - blue component as an integer value from 0 to 255

Pavyzdžiai

  • color_rgb(255,127,0) → ‚255,127,0‘

9.2.3.15. color_rgba

Returns a string representation of a color based on its red, green, blue, and alpha (transparency) components.

Sintaksė

color_rgba(red, green, blue, alpha)

Argumentai

  • red - red component as an integer value from 0 to 255

  • green - green component as an integer value from 0 to 255

  • blue - blue component as an integer value from 0 to 255

  • alpha - alpha component as an integer value from 0 (completely transparent) to 255 (opaque).

Pavyzdžiai

  • color_rgba(255,127,0,200) → ‚255,127,0,200‘

9.2.3.16. color_rgbf

Returns a color object based on its red, green, blue and alpha components.

Sintaksė

color_rgbf(red, green, blue, [alpha=1.0])

[] žymi neprivalomus argumentus

Argumentai

  • red - red component as a float value from 0.0 to 1.0

  • green - green component as a float value from 0.0 to 1.0

  • blue - blue component as a float value from 0.0 to 1.0

  • alpha - alpha component as a float value from 0.0 to 1.0

Pavyzdžiai

  • color_rgbf(1.0,0.5,0) → RGBA: 1.00,0.50,0.00,1.00

9.2.3.17. create_ramp

Returns a gradient ramp from a map of color strings and steps.

Sintaksė

create_ramp(map, [discrete=false])

[] žymi neprivalomus argumentus

Argumentai

  • map - a map of color strings and steps

  • discrete - set this parameter to true to create a discrete color ramp

Pavyzdžiai

  • ramp_color(create_ramp(map(0,'0,0,0',1,'255,0,0')),1) → ‚255,0,0,255‘

9.2.3.18. darker

Returns a darker (or lighter) color. Returned type is the same as color arguments, i.e. a color string representation or a color object.

Sintaksė

darker(color, factor)

Argumentai

  • color - a color string or a color object

  • factor - an integer corresponding to the darkening factor:

    • if the factor is greater than 100, this function returns a darker color (e.g., setting factor to 200 returns a color that is half the brightness);

    • if the factor is less than 100, the return color is lighter, but using the lighter() function for this purpose is recommended;

    • if the factor is 0 or negative, the return value is unspecified.

Pavyzdžiai

  • darker('200,10,30', 200) → ‚100,5,15,255‘

Further reading: lighter

9.2.3.19. lighter

Returns a lighter (or darker) color. Returned type is the same as color arguments, i.e. a color string representation or a color object.

Sintaksė

lighter(color, factor)

Argumentai

  • color - a color string or a color object

  • factor - an integer corresponding to the lightening factor:

    • if the factor is greater than 100, this function returns a lighter color (e.g., setting factor to 150 returns a color that is 50% brighter);

    • if the factor is less than 100, the return color is darker, but using the darker() function for this purpose is recommended;

    • if the factor is 0 or negative, the return value is unspecified.

Pavyzdžiai

  • lighter('200,10,30', 200) → ‚255,158,168,255‘

Further reading: darker

9.2.3.20. project_color

Returns a color from the project’s color scheme.

Sintaksė

project_color(name)

Argumentai

  • name - a color name

Pavyzdžiai

  • project_color('Logo color') → ‚20,140,50‘

Further reading: setting project colors

9.2.3.21. project_color_object

Returns a color from the project’s color scheme. Contrary to project_color which returns a color string representation, project_color_object returns a color object.

Sintaksė

project_color_object(name)

Argumentai

  • name - a color name

Pavyzdžiai

  • project_color_object('Logo color') → RGBA: 0.08,0.55,0.20,1.00

9.2.3.22. ramp_color

Returns a string representing a color from a color ramp.

Saved ramp variant

Returns a string representing a color from a saved ramp

Sintaksė

ramp_color(ramp_name, value)

Argumentai

  • ramp_name - the name of the color ramp as a string, for example ‚Spectral‘

  • value - the position on the ramp to select the color from as a real number between 0 and 1

Pavyzdžiai

  • ramp_color('Spectral',0.3) → ‚253,190,115,255‘

Pastaba

The color ramps available vary between QGIS installations. This function may not give the expected results if you move your QGIS project between installations.

Expression-created ramp variant

Returns a string representing a color from an expression-created ramp

Sintaksė

ramp_color(ramp, value)

Argumentai

  • ramp - the color ramp

  • value - the position on the ramp to select the color from as a real number between 0 and 1

Pavyzdžiai

  • ramp_color(create_ramp(map(0,'0,0,0',1,'255,0,0')),1) → ‚255,0,0,255‘

Further reading: Setting a Color Ramp, Iškrentantis spalvų rampos parinkimas

9.2.3.23. ramp_color_object

Returns a color object from a color ramp. Contrary to ramp_color which returns a color string representation, ramp_color_object returns a color object.

Saved ramp variant

Returns a color object from a saved ramp

Sintaksė

ramp_color_object(ramp_name, value)

Argumentai

  • ramp_name - the name of the color ramp as a string, for example ‚Spectral‘

  • value - the position on the ramp to select the color from as a real number between 0 and 1

Pavyzdžiai

  • ramp_color_object('Spectral',0.3) → RGBA: 0.99,0.75,0.45,1.00

Pastaba

The color ramps available vary between QGIS installations. This function may not give the expected results if you move your QGIS project between installations.

Expression-created ramp variant

Returns a color object from an expression-created ramp

Sintaksė

ramp_color_object(ramp, value)

Argumentai

  • ramp - the color ramp

  • value - the position on the ramp to select the color from as a real number between 0 and 1

Pavyzdžiai

  • ramp_color_object(create_ramp(map(0,color_rgbf(0,0,0),1,color_rgbf(1,0,0))),1) → RGBA: 1.00,0.00,0.00,1.00

9.2.3.24. set_color_part

Sets a specific color component for a color string or a color object, e.g., the red component or alpha component.

Sintaksė

set_color_part(color, component, value)

Argumentai

  • color - a color string or a color object

  • component - a string corresponding to the color component to set. Valid options are:

    • red: RGB red component (0-255)

    • green: RGB green component (0-255)

    • blue: RGB blue component (0-255)

    • alpha: alpha (transparency) value (0-255)

    • hue: HSV hue (0-360)

    • saturation: HSV saturation (0-100)

    • value: HSV value (0-100)

    • hsl_hue: HSL hue (0-360)

    • hsl_saturation: HSL saturation (0-100)

    • lightness: HSL lightness (0-100)

    • cyan: CMYK cyan component (0-100)

    • magenta: CMYK magenta component (0-100)

    • yellow: CMYK yellow component (0-100)

    • black: CMYK black component (0-100)

  • value - new value for color component, respecting the ranges listed above

Pavyzdžiai

  • set_color_part('200,10,30','green',50) → ‚200,50,30,255‘

  • set_color_part(color_cmykf(0.21,0,0.92,0.70),'black',100) → CMYKA: 0.21,0.00,0.92,1.00,1.00

9.2.4. Conditional Functions

This group contains functions to handle conditional checks in expressions.

9.2.4.1. CASE

CASE is used to evaluate a series of conditions and return a result for the first condition met. The conditions are evaluated sequentially, and if a condition is true, the evaluation stops, and the corresponding result is returned. If none of the conditions are true, the value in the ELSE clause is returned. Furthermore, if no ELSE clause is set and none of the conditions are met, NULL is returned.

CASE

WHEN condition THEN result

[ …n ]

[ ELSE result ]

END

[ ] marks optional components

Argumentai

  • WHEN condition - A condition expression to evaluate

  • THEN result - If condition evaluates to True then result is evaluated and returned.

  • ELSE result - If none of the above conditions evaluated to True then result is evaluated and returned.

Pavyzdžiai

  • CASE WHEN "name" IS NULL THEN 'None' END → Returns the string ‚None‘ if the „name“ field is NULL

  • CASE WHEN $area > 10000 THEN 'Big property' WHEN $area > 5000 THEN 'Medium property' ELSE 'Small property' END → Returns the string ‚Big property‘ if the area is bigger than 10000, ‚Medium property‘ if the area is between 5000 and 10000, and ‚Small property‘ for others

9.2.4.2. coalesce

Returns the first non-NULL value from the expression list.

This function can take any number of arguments.

Sintaksė

coalesce(expression1, expression2, …)

Argumentai

  • expression - any valid expression or value, regardless of type.

Pavyzdžiai

  • coalesce(NULL, 2) → 2

  • coalesce(NULL, 2, 3) → 2

  • coalesce(7, NULL, 3*2) → 7

  • coalesce("fieldA", "fallbackField", 'ERROR') → value of fieldA if it is non-NULL else the value of „fallbackField“ or the string ‚ERROR‘ if both are NULL

9.2.4.3. if

Tests a condition and returns a different result depending on the conditional check.

Sintaksė

if(condition, result_when_true, result_when_false)

Argumentai

  • condition - the condition which should be checked

  • result_when_true - the result which will be returned when the condition is true or another value that does not convert to false.

  • result_when_false - the result which will be returned when the condition is false or another value that converts to false like 0 or ‚‘. NULL will also be converted to false.

Pavyzdžiai

  • if( 1+1=2, 'Yes', 'No' ) → ‚Yes‘

  • if( 1+1=3, 'Yes', 'No' ) → ‚No‘

  • if( 5 > 3, 1, 0) → 1

  • if( '', 'It is true (not empty)', 'It is false (empty)' ) → ‚It is false (empty)‘

  • if( ' ', 'It is true (not empty)', 'It is false (empty)' ) → ‚It is true (not empty)‘

  • if( 0, 'One', 'Zero' ) → ‚Zero‘

  • if( 10, 'One', 'Zero' ) → ‚One‘

9.2.4.4. nullif

Returns a NULL value if value1 equals value2; otherwise it returns value1. This can be used to conditionally substitute values with NULL.

Sintaksė

nullif(value1, value2)

Argumentai

  • value1 - The value that should either be used or substituted with NULL.

  • value2 - The control value that will trigger the NULL substitution.

Pavyzdžiai

  • nullif('(none)', '(none)') → NULL

  • nullif('text', '(none)') → ‚text‘

  • nullif("name", '') → NULL, if name is an empty string (or already NULL), the name in any other case.

9.2.4.5. regexp_match

Return the first matching position matching a regular expression within an unicode string, or 0 if the substring is not found.

Sintaksė

regexp_match(input_string, regex)

Argumentai

  • input_string - the string to test against the regular expression

  • regex - The regular expression to test against. Backslash characters must be double escaped (e.g., „\\s“ to match a white space character or „\\b“ to match a word boundary).

Pavyzdžiai

  • regexp_match('QGIS ROCKS','\\sROCKS') → 5

  • regexp_match('Budač','udač\\b') → 2

9.2.4.6. try

Tries an expression and returns its value if error-free. If the expression returns an error, an alternative value will be returned when provided otherwise the function will return NULL.

Sintaksė

try(expression, [alternative])

[] žymi neprivalomus argumentus

Argumentai

  • expression - the expression which should be run

  • alternative - the result which will be returned if the expression returns an error.

Pavyzdžiai

  • try( to_int( '1' ), 0 ) → 1

  • try( to_int( 'a' ), 0 ) → 0

  • try( to_date( 'invalid_date' ) ) → NULL

9.2.5. Conversions Functions

This group contains functions to convert one data type to another (e.g., string from/to integer, binary from/to string, string to date, …).

9.2.5.1. from_base64

Decodes a string in the Base64 encoding into a binary value.

Sintaksė

from_base64(string)

Argumentai

  • string - the string to decode

Pavyzdžiai

  • from_base64('UUdJUw==') → ‚QGIS‘

9.2.5.2. hash

Creates a hash from a string with a given method. One byte (8 bits) is represented with two hex ‚‘digits‘‘, so ‚md4‘ (16 bytes) produces a 16 * 2 = 32 character long hex string and ‚keccak_512‘ (64 bytes) produces a 64 * 2 = 128 character long hex string.

Sintaksė

hash(string, method)

Argumentai

  • string - the string to hash

  • method - The hash method among ‚md4‘, ‚md5‘, ‚sha1‘, ‚sha224‘, ‚sha384‘, ‚sha512‘, ‚sha3_224‘, ‚sha3_256‘, ‚sha3_384‘, ‚sha3_512‘, ‚keccak_224‘, ‚keccak_256‘, ‚keccak_384‘, ‚keccak_512‘

Pavyzdžiai

  • hash('QGIS', 'md4') → ‚c0fc71c241cdebb6e888cbac0e2b68eb‘

  • hash('QGIS', 'md5') → ‚57470aaa9e22adaefac7f5f342f1c6da‘

  • hash('QGIS', 'sha1') → ‚f87cfb2b74cdd5867db913237024e7001e62b114‘

  • hash('QGIS', 'sha224') → ‚4093a619ada631c770f44bc643ead18fb393b93d6a6af1861fcfece0‘

  • hash('QGIS', 'sha256') → ‚eb045cba7a797aaa06ac58830846e40c8e8c780bc0676d3393605fae50c05309‘

  • hash('QGIS', 'sha384') → ‚91c1de038cc3d09fdd512e99f9dd9922efadc39ed21d3922e69a4305cc25506033aee388e554b78714c8734f9cd7e610‘

  • hash('QGIS', 'sha512') → ‚c2c092f2ab743bf8edbeb6d028a745f30fc720408465ed369421f0a4e20fa5e27f0c90ad72d3f1d836eaa5d25cd39897d4cf77e19984668ef58da6e3159f18ac‘

  • hash('QGIS', 'sha3_224') → ‚467f49a5039e7280d5d42fd433e80d203439e338eaabd701f0d6c17d‘

  • hash('QGIS', 'sha3_256') → ‚540f7354b6b8a6e735f2845250f15f4f3ba4f666c55574d9e9354575de0e980f‘

  • hash('QGIS', 'sha3_384') → ‚96052da1e77679e9a65f60d7ead961b287977823144786386eb43647b0901fd8516fa6f1b9d243fb3f28775e6dde6107‘

  • hash('QGIS', 'sha3_512') → ‚900d079dc69761da113980253aa8ac0414a8bd6d09879a916228f8743707c4758051c98445d6b8945ec854ff90655005e02aceb0a2ffc6a0ebf818745d665349‘

  • hash('QGIS', 'keccak_224') → ‚5b0ce6acef8b0a121d4ac4f3eaa8503c799ad4e26a3392d1fb201478‘

  • hash('QGIS', 'keccak_256') → ‚991c520aa6815392de24087f61b2ae0fd56abbfeee4a8ca019c1011d327c577e‘

  • hash('QGIS', 'keccak_384') → ‚c57a3aed9d856fa04e5eeee9b62b6e027cca81ba574116d3cc1f0d48a1ef9e5886ff463ea8d0fac772ee473bf92f810d‘

9.2.5.3. md5

Creates a md5 hash from a string.

Sintaksė

md5(string)

Argumentai

  • string - the string to hash

Pavyzdžiai

  • md5('QGIS') → ‚57470aaa9e22adaefac7f5f342f1c6da‘

9.2.5.4. sha256

Creates a sha256 hash from a string.

Sintaksė

sha256(string)

Argumentai

  • string - the string to hash

Pavyzdžiai

  • sha256('QGIS') → ‚eb045cba7a797aaa06ac58830846e40c8e8c780bc0676d3393605fae50c05309‘

9.2.5.5. to_base64

Encodes a binary value into a string, using the Base64 encoding.

Sintaksė

to_base64(value)

Argumentai

  • value - the binary value to encode

Pavyzdžiai

  • to_base64('QGIS') → ‚UUdJUw==‘

9.2.5.6. to_date

Converts a string into a date object. An optional format string can be provided to parse the string; see QDate::fromString or the documentation of the format_date function for additional documentation on the format. By default the current QGIS user locale is used.

Sintaksė

to_date(string, [format], [language])

[] žymi neprivalomus argumentus

Argumentai

  • string - string representing a date value

  • format - format used to convert the string into a date

  • language - language (lowercase, two- or three-letter, ISO 639 language code) used to convert the string into a date. By default the current QGIS user locale is used.

Pavyzdžiai

  • to_date('2012-05-04') → 2012-05-04

  • to_date('June 29, 2019','MMMM d, yyyy') → 2019-06-29, if the current locale uses the name ‚June‘ for the sixth month, otherwise an error occurs

  • to_date('29 juin, 2019','d MMMM, yyyy','fr') → 2019-06-29

Further reading: format_date

9.2.5.7. to_datetime

Converts a string into a datetime object. An optional format string can be provided to parse the string; see QDate::fromString, QTime::fromString or the documentation of the format_date function for additional documentation on the format. By default the current QGIS user locale is used.

Sintaksė

to_datetime(string, [format], [language])

[] žymi neprivalomus argumentus

Argumentai

  • string - string representing a datetime value

  • format - format used to convert the string into a datetime

  • language - language (lowercase, two- or three-letter, ISO 639 language code) used to convert the string into a datetime. By default the current QGIS user locale is used.

Pavyzdžiai

  • to_datetime('2012-05-04 12:50:00') → 2012-05-04T12:50:00

  • to_datetime('June 29, 2019 @ 12:34','MMMM d, yyyy @ HH:mm') → 2019-06-29T12:34, if the current locale uses the name ‚June‘ for the sixth month, otherwise an error occurs

  • to_datetime('29 juin, 2019 @ 12:34','d MMMM, yyyy @ HH:mm','fr') → 2019-06-29T12:34

Further reading: format_date

9.2.5.8. to_decimal

Converts a degree, minute, second coordinate to its decimal equivalent.

Sintaksė

to_decimal(value)

Argumentai

  • value - A degree, minute, second string.

Pavyzdžiai

  • to_decimal('6°21\'16.445') → 6.3545680555

9.2.5.9. to_dm

Converts a coordinate to degree, minute.

Sintaksė

to_dm(coordinate, axis, precision, [formatting=])

[] žymi neprivalomus argumentus

Argumentai

  • coordinate - A latitude or longitude value.

  • axis - The axis of the coordinate. Either ‚x‘ or ‚y‘.

  • precision - Number of decimals.

  • formatting - Designates the formatting type. Acceptable values are NULL (default), ‚aligned‘ or ‚suffix‘.

Pavyzdžiai

  • to_dm(6.1545681, 'x', 3) → 6°9.274′

  • to_dm(6.1545681, 'y', 4, 'aligned') → 6°09.2741′N

  • to_dm(6.1545681, 'y', 4, 'suffix') → 6°9.2741′N

9.2.5.10. to_dms

Converts a coordinate to degree, minute, second.

Sintaksė

to_dms(coordinate, axis, precision, [formatting=])

[] žymi neprivalomus argumentus

Argumentai

  • coordinate - A latitude or longitude value.

  • axis - The axis of the coordinate. Either ‚x‘ or ‚y‘.

  • precision - Number of decimals.

  • formatting - Designates the formatting type. Acceptable values are NULL (default), ‚aligned‘ or ‚suffix‘.

Pavyzdžiai

  • to_dms(6.1545681, 'x', 3) → 6°9′16.445″

  • to_dms(6.1545681, 'y', 4, 'aligned') → 6°09′16.4452″N

  • to_dms(6.1545681, 'y', 4, 'suffix') → 6°9′16.4452″N

9.2.5.11. to_int

Converts a string to integer number. If a value cannot be converted to integer the expression is invalid (e.g ‚123asd‘ is invalid).

Sintaksė

to_int(string)

Argumentai

  • string - string to convert to integer number

Pavyzdžiai

  • to_int('123') → 123

9.2.5.12. to_interval

Converts a string to an interval type. Can be used to take days, hours, month, etc of a date.

Sintaksė

to_interval(string)

Argumentai

  • string - a string representing an interval. Allowable formats include {n} days {n} hours {n} months.

Pavyzdžiai

  • to_interval('1 day 2 hours') → interval: 1.08333 days

  • to_interval( '0.5 hours' ) → interval: 30 minutes

  • to_datetime('2012-05-05 12:00:00') - to_interval('1 day 2 hours') → 2012-05-04T10:00:00

9.2.5.13. to_real

Converts a string to a real number. If a value cannot be converted to real the expression is invalid (e.g ‚123.56asd‘ is invalid). Numbers are rounded after saving changes if the precision is smaller than the result of the conversion.

Sintaksė

to_real(string)

Argumentai

  • string - string to convert to real number

Pavyzdžiai

  • to_real('123.45') → 123.45

9.2.5.14. to_string

Converts a number to string.

Sintaksė

to_string(number)

Argumentai

  • number - Integer or real value. The number to convert to string.

Pavyzdžiai

  • to_string(123) → ‚123‘

Further reading: format_number

9.2.5.15. to_time

Converts a string into a time object. An optional format string can be provided to parse the string; see QTime::fromString for additional documentation on the format.

Sintaksė

to_time(string, [format], [language])

[] žymi neprivalomus argumentus

Argumentai

  • string - string representing a time value

  • format - format used to convert the string into a time

  • language - language (lowercase, two- or three-letter, ISO 639 language code) used to convert the string into a time

Pavyzdžiai

  • to_time('12:30:01') → 12:30:01

  • to_time('12:34','HH:mm') → 12:34:00

  • to_time('12:34','HH:mm','fr') → 12:34:00

Further reading: format_date

9.2.6. Custom Functions

This group contains functions created by the user. See Funkcijų redaktorius for more details.

9.2.7. Date and Time Functions

This group contains functions for handling date and time data. This group shares several functions with the Conversions Functions (to_date, to_time, to_datetime, to_interval) and String Functions (format_date) groups.

Pastaba

Storing date, datetime and intervals on fields

The ability to store date, time and datetime values directly on fields depends on the data source’s provider (e.g., Shapefile accepts date format, but not datetime or time format). The following are some suggestions to overcome this limitation:

  • date, datetime and time can be converted and stored in text type fields using the format_date() function.

  • Intervals can be stored in integer or decimal type fields after using one of the date extraction functions (e.g., day() to get the interval expressed in days)

9.2.7.1. age

Returns the difference between two dates or datetimes.

The difference is returned as an Interval and needs to be used with one of the following functions in order to extract useful information:

  • year

  • month

  • week

  • day

  • hour

  • minute

  • second

Sintaksė

age(datetime1, datetime2)

Argumentai

  • datetime1 - a string, date or datetime representing the later date

  • datetime2 - a string, date or datetime representing the earlier date

Pavyzdžiai

  • day(age('2012-05-12','2012-05-02')) → 10

  • hour(age('2012-05-12','2012-05-02')) → 240

9.2.7.2. datetime_from_epoch

Returns a datetime whose date and time are the number of milliseconds, msecs, that have passed since 1970-01-01T00:00:00.000, Coordinated Universal Time (Qt.UTC), and converted to Qt.LocalTime.

Sintaksė

datetime_from_epoch(int)

Argumentai

  • int - number (milliseconds)

Pavyzdžiai

  • datetime_from_epoch(1483225200000) → 2017-01-01T00:00:00

9.2.7.3. day

Extracts the day from a date, or the number of days from an interval.

Date variant

Extracts the day from a date or datetime.

Sintaksė

day(date)

Argumentai

  • date - a date or datetime value

Pavyzdžiai

  • day('2012-05-12') → 12

Interval variant

Calculates the length in days of an interval.

Sintaksė

day(interval)

Argumentai

  • interval - interval value to return number of days from

Pavyzdžiai

  • day(to_interval('3 days')) → 3

  • day(to_interval('3 weeks 2 days')) → 23

  • day(age('2012-01-01','2010-01-01')) → 730

9.2.7.4. day_of_week

Returns the day of the week for a specified date or datetime. The returned value ranges from 0 to 6, where 0 corresponds to a Sunday and 6 to a Saturday.

Sintaksė

day_of_week(date)

Argumentai

  • date - date or datetime value

Pavyzdžiai

  • day_of_week(to_date('2015-09-21')) → 1

9.2.7.5. epoch

Returns the interval in milliseconds between the unix epoch and a given date value.

Sintaksė

epoch(date)

Argumentai

  • date - a date or datetime value

Pavyzdžiai

  • epoch(to_date('2017-01-01')) → 1483203600000

9.2.7.6. format_date

Formats a date type or string into a custom string format. Uses Qt date/time format strings. See QDateTime::toString.

Sintaksė

format_date(datetime, format, [language])

[] žymi neprivalomus argumentus

Argumentai

  • datetime - date, time or datetime value

  • format - String template used to format the string.

    Expression

    Output

    d

    the day as number without a leading zero (1 to 31)

    dd

    the day as number with a leading zero (01 to 31)

    ddd

    the abbreviated localized day name (e.g. ‚Mon‘ to ‚Sun‘)

    dddd

    the long localized day name (e.g. ‚Monday‘ to ‚Sunday‘)

    M

    the month as number without a leading zero (1-12)

    MM

    the month as number with a leading zero (01-12)

    MMM

    the abbreviated localized month name (e.g. ‚Jan‘ to ‚Dec‘)

    MMMM

    the long localized month name (e.g. ‚January‘ to ‚December‘)

    yy

    the year as two digit number (00-99)

    yyyy

    the year as four digit number

    These expressions may be used for the time part of the format string:

    Expression

    Output

    h

    the hour without a leading zero (0 to 23 or 1 to 12 if AM/PM display)

    hh

    the hour with a leading zero (00 to 23 or 01 to 12 if AM/PM display)

    H

    the hour without a leading zero (0 to 23, even with AM/PM display)

    HH

    the hour with a leading zero (00 to 23, even with AM/PM display)

    m

    the minute without a leading zero (0 to 59)

    mm

    the minute with a leading zero (00 to 59)

    s

    the second without a leading zero (0 to 59)

    ss

    the second with a leading zero (00 to 59)

    z

    the milliseconds without trailing zeroes (0 to 999)

    zzz

    the milliseconds with trailing zeroes (000 to 999)

    AP or A

    interpret as an AM/PM time. AP must be either ‚AM‘ or ‚PM‘.

    ap or a

    Interpret as an AM/PM time. ap must be either ‚am‘ or ‚pm‘.

  • language - language (lowercase, two- or three-letter, ISO 639 language code) used to format the date into a custom string. By default the current QGIS user locale is used.

Pavyzdžiai

  • format_date('2012-05-15','dd.MM.yyyy') → ‚15.05.2012‘

  • format_date('2012-05-15','d MMMM yyyy','fr') → ‚15 mai 2012‘

  • format_date('2012-05-15','dddd') → ‚Tuesday‘, if the current locale is an English variant

  • format_date('2012-05-15 13:54:20','dd.MM.yy') → ‚15.05.12‘

  • format_date('13:54:20','hh:mm AP') → ‚01:54 PM‘

9.2.7.7. hour

Extracts the hour part from a datetime or time, or the number of hours from an interval.

Time variant

Extracts the hour part from a time or datetime.

Sintaksė

hour(datetime)

Argumentai

  • datetime - a time or datetime value

Pavyzdžiai

  • hour( to_datetime('2012-07-22 13:24:57') ) → 13

Interval variant

Calculates the length in hours of an interval.

Sintaksė

hour(interval)

Argumentai

  • interval - interval value to return number of hours from

Pavyzdžiai

  • hour(to_interval('3 hours')) → 3

  • hour(age('2012-07-22T13:00:00','2012-07-22T10:00:00')) → 3

  • hour(age('2012-01-01','2010-01-01')) → 17520

9.2.7.8. make_date

Creates a date value from year, month and day numbers.

Sintaksė

make_date(year, month, day)

Argumentai

  • year - Year number. Years 1 to 99 are interpreted as is. Year 0 is invalid.

  • month - Month number, where 1=January

  • day - Day number, beginning with 1 for the first day in the month

Pavyzdžiai

  • make_date(2020,5,4) → date value 2020-05-04

9.2.7.9. make_datetime

Creates a datetime value from year, month, day, hour, minute and second numbers.

Sintaksė

make_datetime(year, month, day, hour, minute, second)

Argumentai

  • year - Year number. Years 1 to 99 are interpreted as is. Year 0 is invalid.

  • month - Month number, where 1=January

  • day - Day number, beginning with 1 for the first day in the month

  • hour - Hour number

  • minute - Minutes

  • second - Seconds (fractional values include milliseconds)

Pavyzdžiai

  • make_datetime(2020,5,4,13,45,30.5) → datetime value 2020-05-04 13:45:30.500

9.2.7.10. make_interval

Creates an interval value from year, month, weeks, days, hours, minute and seconds values.

Sintaksė

make_interval([years=0], [months=0], [weeks=0], [days=0], [hours=0], [minutes=0], [seconds=0])

[] žymi neprivalomus argumentus

Argumentai

  • years - Number of years (assumes a 365.25 day year length).

  • months - Number of months (assumes a 30 day month length)

  • weeks - Number of weeks

  • days - Number of days

  • hours - Number of hours

  • minutes - Number of minutes

  • seconds - Number of seconds

Pavyzdžiai

  • make_interval(hours:=3) → interval: 3 hours

  • make_interval(days:=2, hours:=3) → interval: 2.125 days

  • make_interval(minutes:=0.5, seconds:=5) → interval: 35 seconds

9.2.7.11. make_time

Creates a time value from hour, minute and second numbers.

Sintaksė

make_time(hour, minute, second)

Argumentai

  • hour - Hour number

  • minute - Minutes

  • second - Seconds (fractional values include milliseconds)

Pavyzdžiai

  • make_time(13,45,30.5) → time value 13:45:30.500

9.2.7.12. minute

Extracts the minutes part from a datetime or time, or the number of minutes from an interval.

Time variant

Extracts the minutes part from a time or datetime.

Sintaksė

minute(datetime)

Argumentai

  • datetime - a time or datetime value

Pavyzdžiai

  • minute( to_datetime('2012-07-22 13:24:57') ) → 24

Interval variant

Calculates the length in minutes of an interval.

Sintaksė

minute(interval)

Argumentai

  • interval - interval value to return number of minutes from

Pavyzdžiai

  • minute(to_interval('3 minutes')) → 3

  • minute(age('2012-07-22T00:20:00','2012-07-22T00:00:00')) → 20

  • minute(age('2012-01-01','2010-01-01')) → 1051200

9.2.7.13. month

Extracts the month part from a date, or the number of months from an interval.

Date variant

Extracts the month part from a date or datetime.

Sintaksė

month(date)

Argumentai

  • date - a date or datetime value

Pavyzdžiai

  • month('2012-05-12') → 05

Interval variant

Calculates the length in months of an interval.

Sintaksė

month(interval)

Argumentai

  • interval - interval value to return number of months from

Pavyzdžiai

  • month(to_interval('3 months')) → 3

  • month(age('2012-01-01','2010-01-01')) → 4.03333

9.2.7.14. now

Returns the current date and time. The function is static and will return consistent results while evaluating. The time returned is the time when the expression is prepared.

Sintaksė

now()

Pavyzdžiai

  • now() → 2012-07-22T13:24:57

9.2.7.15. second

Extracts the seconds part from a datetime or time, or the number of seconds from an interval.

Time variant

Extracts the seconds part from a time or datetime.

Sintaksė

second(datetime)

Argumentai

  • datetime - a time or datetime value

Pavyzdžiai

  • second( to_datetime('2012-07-22 13:24:57') ) → 57

Interval variant

Calculates the length in seconds of an interval.

Sintaksė

second(interval)

Argumentai

  • interval - interval value to return number of seconds from

Pavyzdžiai

  • second(to_interval('3 minutes')) → 180

  • second(age('2012-07-22T00:20:00','2012-07-22T00:00:00')) → 1200

  • second(age('2012-01-01','2010-01-01')) → 63072000

9.2.7.16. to_date

Converts a string into a date object. An optional format string can be provided to parse the string; see QDate::fromString or the documentation of the format_date function for additional documentation on the format. By default the current QGIS user locale is used.

Sintaksė

to_date(string, [format], [language])

[] žymi neprivalomus argumentus

Argumentai

  • string - string representing a date value

  • format - format used to convert the string into a date

  • language - language (lowercase, two- or three-letter, ISO 639 language code) used to convert the string into a date. By default the current QGIS user locale is used.

Pavyzdžiai

  • to_date('2012-05-04') → 2012-05-04

  • to_date('June 29, 2019','MMMM d, yyyy') → 2019-06-29, if the current locale uses the name ‚June‘ for the sixth month, otherwise an error occurs

  • to_date('29 juin, 2019','d MMMM, yyyy','fr') → 2019-06-29

Further reading: format_date

9.2.7.17. to_datetime

Converts a string into a datetime object. An optional format string can be provided to parse the string; see QDate::fromString, QTime::fromString or the documentation of the format_date function for additional documentation on the format. By default the current QGIS user locale is used.

Sintaksė

to_datetime(string, [format], [language])

[] žymi neprivalomus argumentus

Argumentai

  • string - string representing a datetime value

  • format - format used to convert the string into a datetime

  • language - language (lowercase, two- or three-letter, ISO 639 language code) used to convert the string into a datetime. By default the current QGIS user locale is used.

Pavyzdžiai

  • to_datetime('2012-05-04 12:50:00') → 2012-05-04T12:50:00

  • to_datetime('June 29, 2019 @ 12:34','MMMM d, yyyy @ HH:mm') → 2019-06-29T12:34, if the current locale uses the name ‚June‘ for the sixth month, otherwise an error occurs

  • to_datetime('29 juin, 2019 @ 12:34','d MMMM, yyyy @ HH:mm','fr') → 2019-06-29T12:34

Further reading: format_date

9.2.7.18. to_interval

Converts a string to an interval type. Can be used to take days, hours, month, etc of a date.

Sintaksė

to_interval(string)

Argumentai

  • string - a string representing an interval. Allowable formats include {n} days {n} hours {n} months.

Pavyzdžiai

  • to_interval('1 day 2 hours') → interval: 1.08333 days

  • to_interval( '0.5 hours' ) → interval: 30 minutes

  • to_datetime('2012-05-05 12:00:00') - to_interval('1 day 2 hours') → 2012-05-04T10:00:00

9.2.7.19. to_time

Converts a string into a time object. An optional format string can be provided to parse the string; see QTime::fromString for additional documentation on the format.

Sintaksė

to_time(string, [format], [language])

[] žymi neprivalomus argumentus

Argumentai

  • string - string representing a time value

  • format - format used to convert the string into a time

  • language - language (lowercase, two- or three-letter, ISO 639 language code) used to convert the string into a time

Pavyzdžiai

  • to_time('12:30:01') → 12:30:01

  • to_time('12:34','HH:mm') → 12:34:00

  • to_time('12:34','HH:mm','fr') → 12:34:00

Further reading: format_date

9.2.7.20. week

Extracts the week number from a date, or the number of weeks from an interval.

Date variant

Extracts the week number from a date or datetime.

Sintaksė

week(date)

Argumentai

  • date - a date or datetime value

Pavyzdžiai

  • week('2012-05-12') → 19

Interval variant

Calculates the length in weeks of an interval.

Sintaksė

week(interval)

Argumentai

  • interval - interval value to return number of months from

Pavyzdžiai

  • week(to_interval('3 weeks')) → 3

  • week(age('2012-01-01','2010-01-01')) → 104.285

9.2.7.21. year

Extracts the year part from a date, or the number of years from an interval.

Date variant

Extracts the year part from a date or datetime.

Sintaksė

year(date)

Argumentai

  • date - a date or datetime value

Pavyzdžiai

  • year('2012-05-12') → 2012

Interval variant

Calculates the length in years of an interval.

Sintaksė

year(interval)

Argumentai

  • interval - interval value to return number of years from

Pavyzdžiai

  • year(to_interval('3 years')) → 3

  • year(age('2012-01-01','2010-01-01')) → 1.9986

Some examples:

Besides these functions, subtracting dates, datetimes or times using the - (minus) operator will return an interval.

Adding or subtracting an interval to dates, datetimes or times, using the + (plus) and - (minus) operators, will return a datetime.

  • Get the number of days until QGIS 3.0 release:

    to_date('2017-09-29') - to_date(now())
    -- Returns <interval: 203 days>
    
  • The same with time:

    to_datetime('2017-09-29 12:00:00') - now()
    -- Returns <interval: 202.49 days>
    
  • Get the datetime of 100 days from now:

    now() + to_interval('100 days')
    -- Returns <datetime: 2017-06-18 01:00:00>
    

9.2.8. Fields and Values

Contains a list of fields from the active layer, and special values. Fields list includes the ones stored in the dataset, virtual and auxiliary ones as well as from joins.

Double-click a field name to have it added to your expression. You can also type the field name (preferably inside double quotes) or its alias.

To retrieve fields values to use in an expression, select the appropriate field and, in the shown widget, choose between 10 Samples and All Unique. Requested values are then displayed and you can use the Search box at the top of the list to filter the result. Sample values can also be accessed via right-clicking on a field.

To add a value to the expression you are writing, double-click on it in the list. If the value is of a string type, it should be simple quoted, otherwise no quote is needed.

9.2.8.1. NULL

Equates to a NULL value.

Sintaksė

NULL

Pavyzdžiai

  • NULL → a NULL value

Pastaba

To test for NULL use an IS NULL or IS NOT NULL expression.

9.2.9. Files and Paths Functions

This group contains functions which manipulate file and path names.

9.2.9.1. base_file_name

Returns the base name of the file without the directory or file suffix.

Sintaksė

base_file_name(path)

Argumentai

  • path - a file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

Pavyzdžiai

  • base_file_name('/home/qgis/data/country_boundaries.shp') → ‚country_boundaries‘

9.2.9.2. exif

Retrieves exif tag values from an image file.

Sintaksė

exif(path, [tag])

[] žymi neprivalomus argumentus

Argumentai

  • path - An image file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

  • tag - The tag to return. If empty, a map with all exif tag values will be returned.

Pavyzdžiai

  • exif('/my/photo.jpg','Exif.Image.Orientation') → 0

9.2.9.3. file_exists

Returns TRUE if a file path exists.

Sintaksė

file_exists(path)

Argumentai

  • path - a file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

Pavyzdžiai

  • file_exists('/home/qgis/data/country_boundaries.shp') → TRUE

9.2.9.4. file_name

Returns the name of a file (including the file extension), excluding the directory.

Sintaksė

file_name(path)

Argumentai

  • path - a file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

Pavyzdžiai

  • file_name('/home/qgis/data/country_boundaries.shp') → ‚country_boundaries.shp‘

9.2.9.5. file_path

Returns the directory component of a file path. This does not include the file name.

Sintaksė

file_path(path)

Argumentai

  • path - a file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

Pavyzdžiai

  • file_path('/home/qgis/data/country_boundaries.shp') → ‚/home/qgis/data‘

9.2.9.6. file_size

Returns the size (in bytes) of a file.

Sintaksė

file_size(path)

Argumentai

  • path - a file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

Pavyzdžiai

  • file_size('/home/qgis/data/country_boundaries.geojson') → 5674

9.2.9.7. file_suffix

Returns the file suffix (extension) from a file path.

Sintaksė

file_suffix(path)

Argumentai

  • path - a file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

Pavyzdžiai

  • file_suffix('/home/qgis/data/country_boundaries.shp') → ‚shp‘

9.2.9.8. is_directory

Returns TRUE if a path corresponds to a directory.

Sintaksė

is_directory(path)

Argumentai

  • path - a file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

Pavyzdžiai

  • is_directory('/home/qgis/data/country_boundaries.shp') → FALSE

  • is_directory('/home/qgis/data/') → TRUE

9.2.9.9. is_file

Returns TRUE if a path corresponds to a file.

Sintaksė

is_file(path)

Argumentai

  • path - a file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

Pavyzdžiai

  • is_file('/home/qgis/data/country_boundaries.shp') → TRUE

  • is_file('/home/qgis/data/') → FALSE

9.2.10. Form Functions

This group contains functions that operate exclusively under the attribute form context. For example, in field’s widgets settings.

9.2.10.1. current_parent_value

Only usable in an embedded form context, this function returns the current, unsaved value of a field in the parent form currently being edited. This will differ from the parent feature’s actual attribute values for features which are currently being edited or have not yet been added to a parent layer. When used in a value-relation widget filter expression, this function should be wrapped into a ‚coalesce()‘ that can retrieve the actual parent feature from the layer when the form is not used in an embedded context.

Sintaksė

current_parent_value(field_name)

Argumentai

  • field_name - a field name in the current parent form

Pavyzdžiai

  • current_parent_value( 'FIELD_NAME' ) → The current value of a field ‚FIELD_NAME‘ in the parent form.

9.2.10.2. current_value

Returns the current, unsaved value of a field in the form or table row currently being edited. This will differ from the feature’s actual attribute values for features which are currently being edited or have not yet been added to a layer.

Sintaksė

current_value(field_name)

Argumentai

  • field_name - a field name in the current form or table row

Pavyzdžiai

  • current_value( 'FIELD_NAME' ) → The current value of field ‚FIELD_NAME‘.

9.2.11. Fuzzy Matching Functions

This group contains functions for fuzzy comparisons between values.

9.2.11.1. hamming_distance

Returns the Hamming distance between two strings. This equates to the number of characters at corresponding positions within the input strings where the characters are different. The input strings must be the same length, and the comparison is case-sensitive.

Sintaksė

hamming_distance(string1, string2)

Argumentai

  • string1 - a string

  • string2 - a string

Pavyzdžiai

  • hamming_distance('abc','xec') → 2

  • hamming_distance('abc','ABc') → 2

  • hamming_distance(upper('abc'),upper('ABC')) → 0

  • hamming_distance('abc','abcd') → NULL

9.2.11.2. levenshtein

Returns the Levenshtein edit distance between two strings. This equates to the minimum number of character edits (insertions, deletions or substitutions) required to change one string to another.

The Levenshtein distance is a measure of the similarity between two strings. Smaller distances mean the strings are more similar, and larger distances indicate more different strings. The distance is case sensitive.

Sintaksė

levenshtein(string1, string2)

Argumentai

  • string1 - a string

  • string2 - a string

Pavyzdžiai

  • levenshtein('kittens','mitten') → 2

  • levenshtein('Kitten','kitten') → 1

  • levenshtein(upper('Kitten'),upper('kitten')) → 0

9.2.11.3. longest_common_substring

Returns the longest common substring between two strings. This substring is the longest string that is a substring of the two input strings. For example, the longest common substring of „ABABC“ and „BABCA“ is „BABC“. The substring is case sensitive.

Sintaksė

longest_common_substring(string1, string2)

Argumentai

  • string1 - a string

  • string2 - a string

Pavyzdžiai

  • longest_common_substring('ABABC','BABCA') → ‚BABC‘

  • longest_common_substring('abcDeF','abcdef') → ‚abc‘

  • longest_common_substring(upper('abcDeF'),upper('abcdex')) → ‚ABCDE‘

9.2.11.4. soundex

Returns the Soundex representation of a string. Soundex is a phonetic matching algorithm, so strings with similar sounds should be represented by the same Soundex code.

Sintaksė

soundex(string)

Argumentai

  • string - a string

Pavyzdžiai

  • soundex('robert') → ‚R163‘

  • soundex('rupert') → ‚R163‘

  • soundex('rubin') → ‚R150‘

9.2.12. General Functions

This group contains general assorted functions.

9.2.12.1. env

Gets an environment variable and returns its content as a string. If the variable is not found, NULL will be returned. This is handy to inject system specific configuration like drive letters or path prefixes. Definition of environment variables depends on the operating system, please check with your system administrator or the operating system documentation how this can be set.

Sintaksė

env(name)

Argumentai

  • name - The name of the environment variable which should be retrieved.

Pavyzdžiai

  • env( 'LANG' ) → ‚en_US.UTF-8‘

  • env( 'MY_OWN_PREFIX_VAR' ) → ‚Z:‘

  • env( 'I_DO_NOT_EXIST' ) → NULL

9.2.12.2. eval

Evaluates an expression which is passed in a string. Useful to expand dynamic parameters passed as context variables or fields.

Sintaksė

eval(expression)

Argumentai

  • expression - an expression string

Pavyzdžiai

  • eval('\'nice\'') → ‚nice‘

  • eval(@expression_var) → [whatever the result of evaluating @expression_var might be…]

9.2.12.3. eval_template

Evaluates a template which is passed in a string. Useful to expand dynamic parameters passed as context variables or fields.

Sintaksė

eval_template(template)

Argumentai

  • template - a template string

Pavyzdžiai

  • eval_template('QGIS [% upper(\'rocks\') %]') → QGIS ROCKS

9.2.12.4. is_layer_visible

Returns TRUE if a specified layer is visible.

Sintaksė

is_layer_visible(layer)

Argumentai

  • layer - tekstas, reprezentuojantis arba sluoksnio pavadinimą, arba sluoksnio ID

Pavyzdžiai

  • is_layer_visible('baseraster') → TRUE

9.2.12.5. mime_type

Returns the mime type of the binary data.

Sintaksė

mime_type(bytes)

Argumentai

  • bytes - the binary data

Pavyzdžiai

  • mime_type('<html><body></body></html>') → text/html

  • mime_type(from_base64('R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAIAOw==')) → image/gif

9.2.12.6. var

Returns the value stored within a specified variable.

Sintaksė

var(name)

Argumentai

  • name - a variable name

Pavyzdžiai

  • var('qgis_version') → ‚2.12‘

Further reading: List of default variables

9.2.12.7. with_variable

This function sets a variable for any expression code that will be provided as 3rd argument. This is only useful for complicated expressions, where the same calculated value needs to be used in different places.

Sintaksė

with_variable(name, value, expression)

Argumentai

  • name - the name of the variable to set

  • value - the value to set

  • expression - the expression for which the variable will be available

Pavyzdžiai

  • with_variable('my_sum', 1 + 2 + 3, @my_sum * 2 + @my_sum * 5) → 42

9.2.13. Geometry Functions

This group contains functions that operate on geometry objects (e.g. buffer, transform, $area).

9.2.13.1. affine_transform

Returns the geometry after an affine transformation. Calculations are in the Spatial Reference System of this geometry. The operations are performed in a scale, rotation, translation order. If there is a Z or M offset but the coordinate is not present in the geometry, it will be added.

Sintaksė

affine_transform(geometry, delta_x, delta_y, rotation_z, scale_x, scale_y, [delta_z=0], [delta_m=0], [scale_z=1], [scale_m=1])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • delta_x - x-axis translation

  • delta_y - y-axis translation

  • rotation_z - rotation around z-axis in degrees counter-clockwise

  • scale_x - x-axis scale factor

  • scale_y - y-axis scale factor

  • delta_z - z-axis translation

  • delta_m - m-axis translation

  • scale_z - z-axis scale factor

  • scale_m - m-axis scale factor

Pavyzdžiai

  • geom_to_wkt(affine_transform(geom_from_wkt('LINESTRING(1 1, 2 2)'), 2, 2, 0, 1, 1)) → ‚LineString (3 3, 4 4)‘

  • geom_to_wkt(affine_transform(geom_from_wkt('POLYGON((0 0, 0 3, 2 2, 0 0))'), 0, 0, -90, 1, 2)) → ‚Polygon ((0 0, 6 0, 4 -2, 0 0))‘

  • geom_to_wkt(affine_transform(geom_from_wkt('POINT(3 1)'), 0, 0, 0, 1, 1, 5, 0)) → ‚PointZ (3 1 5)‘

../../../_images/affinetransform.png

Fig. 9.4 Vektorinis taškų sluoksnis (žali taškai) prieš (kairėje) ir po (dešinėje) paprastos transformacijos (vertimo).

9.2.13.2. angle_at_vertex

Returns the bisector angle (average angle) to the geometry for a specified vertex on a linestring geometry. Angles are in degrees clockwise from north.

Sintaksė

angle_at_vertex(geometry, vertex)

Argumentai

  • geometry - a linestring geometry

  • vertex - vertex index, starting from 0; if the value is negative, the selected vertex index will be its total count minus the absolute value

Pavyzdžiai

  • angle_at_vertex(geometry:=geom_from_wkt('LineString(0 0, 10 0, 10 10)'),vertex:=1) → 45.0

9.2.13.3. apply_dash_pattern

Applies a dash pattern to a geometry, returning a MultiLineString geometry which is the input geometry stroked along each line/ring with the specified pattern.

Sintaksė

apply_dash_pattern(geometry, pattern, [start_rule=no_rule], [end_rule=no_rule], [adjustment=both], [pattern_offset=0])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry (accepts (multi)linestrings or (multi)polygons).

  • pattern - dash pattern, as an array of numbers representing dash and gap lengths. Must contain an even number of elements.

  • start_rule - optional rule for constraining the start of the pattern. Valid values are ‚no_rule‘, ‚full_dash‘, ‚half_dash‘, ‚full_gap‘, ‚half_gap‘.

  • end_rule - optional rule for constraining the end of the pattern. Valid values are ‚no_rule‘, ‚full_dash‘, ‚half_dash‘, ‚full_gap‘, ‚half_gap‘.

  • adjustment - optional rule for specifying which part of patterns are adjusted to fit the desired pattern rules. Valid values are ‚both‘, ‚dash‘, ‚gap‘.

  • pattern_offset - Optional distance specifying a specific distance along the pattern to commence at.

Pavyzdžiai

  • geom_to_wkt(apply_dash_pattern(geom_from_wkt('LINESTRING(1 1, 10 1)'), array(3, 1))) → MultiLineString ((1 1, 4 1),(5 1, 8 1),(9 1, 10 1, 10 1))

  • geom_to_wkt(apply_dash_pattern(geom_from_wkt('LINESTRING(1 1, 10 1)'), array(3, 1), start_rule:='half_dash')) → MultiLineString ((1 1, 2.5 1),(3.5 1, 6.5 1),(7.5 1, 10 1, 10 1))

9.2.13.4. $area

Returns the area of the current feature. The area calculated by this function respects both the current project’s ellipsoid setting and area unit settings. For example, if an ellipsoid has been set for the project then the calculated area will be ellipsoidal, and if no ellipsoid is set then the calculated area will be planimetric.

Sintaksė

$area

Pavyzdžiai

  • $area → 42

9.2.13.5. area

Returns the area of a geometry polygon object. Calculations are always planimetric in the Spatial Reference System (SRS) of this geometry, and the units of the returned area will match the units for the SRS. This differs from the calculations performed by the $area function, which will perform ellipsoidal calculations based on the project’s ellipsoid and area unit settings.

Sintaksė

area(geometry)

Argumentai

  • geometry - polygon geometry object

Pavyzdžiai

  • area(geom_from_wkt('POLYGON((0 0, 4 0, 4 2, 0 2, 0 0))')) → 8.0

9.2.13.6. azimuth

Returns the north-based azimuth as the angle in radians measured clockwise from the vertical on point_a to point_b.

Sintaksė

azimuth(point_a, point_b)

Argumentai

  • point_a - point geometry

  • point_b - point geometry

Pavyzdžiai

  • degrees( azimuth( make_point(25, 45), make_point(75, 100) ) ) → 42.273689

  • degrees( azimuth( make_point(75, 100), make_point(25,45) ) ) → 222.273689

9.2.13.7. bearing

Returns the north-based bearing as the angle in radians measured clockwise on the ellipsoid from the vertical on point_a to point_b.

Sintaksė

bearing(point_a, point_b, [source_crs], [ellipsoid])

[] žymi neprivalomus argumentus

Argumentai

  • point_a - point geometry

  • point_b - point geometry

  • source_crs - an optional string representing the source CRS of the points. By default the current layer’s CRS is used.

  • ellipsoid - an optional string representing the acronym or the authority:ID (eg ‚EPSG:7030‘) of the ellipsoid on which the bearing should be measured. By default the current project’s ellipsoid setting is used.

Pavyzdžiai

  • degrees( bearing( make_point(16198544, -4534850), make_point(18736872, -1877769), 'EPSG:3857', 'EPSG:7030') ) → 49.980071

  • degrees( bearing( make_point(18736872, -1877769), make_point(16198544, -4534850), 'EPSG:3857', 'WGS84') ) → 219.282386

9.2.13.8. boundary

Returns the closure of the combinatorial boundary of the geometry (ie the topological boundary of the geometry). For instance, a polygon geometry will have a boundary consisting of the linestrings for each ring in the polygon. Some geometry types do not have a defined boundary, e.g., points or geometry collections, and will return NULL.

Sintaksė

boundary(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • geom_to_wkt(boundary(geom_from_wkt('Polygon((1 1, 0 0, -1 1, 1 1))'))) → ‚LineString(1 1,0 0,-1 1,1 1)‘

  • geom_to_wkt(boundary(geom_from_wkt('LineString(1 1,0 0,-1 1)'))) → ‚MultiPoint ((1 1),(-1 1))‘

../../../_images/boundary_polygon.png

Fig. 9.5 Boundary (black dashed line) of the source polygon layer

Further reading: Ribos algorithm

9.2.13.9. bounds

Returns a geometry which represents the bounding box of an input geometry. Calculations are in the Spatial Reference System of this geometry.

Sintaksė

bounds(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • bounds(@geometry) → bounding box of the current feature’s geometry

  • geom_to_wkt(bounds(geom_from_wkt('Polygon((1 1, 0 0, -1 1, 1 1))'))) → ‚Polygon ((-1 0, 1 0, 1 1, -1 1, -1 0))‘

../../../_images/bounding_box.png

Fig. 9.6 Black lines represent the bounding boxes of each polygon feature

Further reading: Bounding boxes algorithm

9.2.13.10. bounds_height

Returns the height of the bounding box of a geometry. Calculations are in the Spatial Reference System of this geometry.

Sintaksė

bounds_height(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • bounds_height(@geometry) → height of bounding box of the current feature’s geometry

  • bounds_height(geom_from_wkt('Polygon((1 1, 0 0, -1 1, 1 1))')) → 1

9.2.13.11. bounds_width

Returns the width of the bounding box of a geometry. Calculations are in the Spatial Reference System of this geometry.

Sintaksė

bounds_width(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • bounds_width(@geometry) → width of bounding box of the current feature’s geometry

  • bounds_width(geom_from_wkt('Polygon((1 1, 0 0, -1 1, 1 1))')) → 2

9.2.13.12. buffer

Returns a geometry that represents all points whose distance from this geometry is less than or equal to distance. Calculations are in the Spatial Reference System of this geometry.

Sintaksė

buffer(geometry, distance, [segments=8], [cap=‘round‘], [join=‘round‘], [miter_limit=2])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • distance - buffer distance in layer units

  • segments - number of segments to use to represent a quarter circle when a round join style is used. A larger number results in a smoother buffer with more nodes.

  • cap - end cap style for buffer. Valid values are ‚round‘, ‚flat‘ or ‚square‘

  • join - join style for buffer. Valid values are ‚round‘, ‚bevel‘ or ‚miter‘.

  • miter_limit - miter distance limit, for use when the join style is set to ‚miter‘

Pavyzdžiai

  • buffer(@geometry, 10.5) → polygon of the current feature’s geometry buffered by 10.5 units

../../../_images/buffer1.png

Fig. 9.7 Buffer (in yellow) of points, line, polygon with positive buffer, and polygon with negative buffer

Further reading: Buffer algorithm

9.2.13.13. buffer_by_m

Creates a buffer along a line geometry where the buffer diameter varies according to the m-values at the line vertices.

Sintaksė

buffer_by_m(geometry, [segments=8])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - input geometry. Must be a (multi)line geometry with m values.

  • segments - number of segments to approximate quarter-circle curves in the buffer.

Pavyzdžiai

  • buffer_by_m(geometry:=geom_from_wkt('LINESTRINGM(1 2 0.5, 4 2 0.2)'),segments:=8) → A variable width buffer starting with a diameter of 0.5 and ending with a diameter of 0.2 along the linestring geometry.

../../../_images/variable_buffer_m.png

Fig. 9.8 Buffering line features using the m value on the vertices

Further reading: Variable width buffer (by M value) algorithm

9.2.13.14. centroid

Returns the geometric center of a geometry.

Sintaksė

centroid(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • centroid(@geometry) → a point geometry

../../../_images/centroids1.png

Fig. 9.9 The red stars represent the centroids of the features of the input layer.

Further reading: Centroids algorithm

9.2.13.15. close_line

Returns a closed line string of the input line string by appending the first point to the end of the line, if it is not already closed. If the geometry is not a line string or multi line string then the result will be NULL.

Sintaksė

close_line(geometry)

Argumentai

  • geometry - a line string geometry

Pavyzdžiai

  • geom_to_wkt(close_line(geom_from_wkt('LINESTRING(0 0, 1 0, 1 1)'))) → ‚LineString (0 0, 1 0, 1 1, 0 0)‘

  • geom_to_wkt(close_line(geom_from_wkt('LINESTRING(0 0, 1 0, 1 1, 0 0)'))) → ‚LineString (0 0, 1 0, 1 1, 0 0)‘

9.2.13.16. closest_point

Returns the point on geometry1 that is closest to geometry2.

Sintaksė

closest_point(geometry1, geometry2)

Argumentai

  • geometry1 - geometry to find closest point on

  • geometry2 - geometry to find closest point to

Pavyzdžiai

  • geom_to_wkt(closest_point(geom_from_wkt('LINESTRING (20 80, 98 190, 110 180, 50 75 )'),geom_from_wkt('POINT(100 100)'))) → ‚Point(73.0769 115.384)‘

9.2.13.17. collect_geometries

Collects a set of geometries into a multi-part geometry object.

List of arguments variant

Geometry parts are specified as separate arguments to the function.

Sintaksė

collect_geometries(geometry1, geometry2, …)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • geom_to_wkt(collect_geometries(make_point(1,2), make_point(3,4), make_point(5,6))) → ‚MultiPoint ((1 2),(3 4),(5 6))‘

Array variant

Geometry parts are specified as an array of geometry parts.

Sintaksė

collect_geometries(array)

Argumentai

  • array - array of geometry objects

Pavyzdžiai

  • geom_to_wkt(collect_geometries(array(make_point(1,2), make_point(3,4), make_point(5,6)))) → ‚MultiPoint ((1 2),(3 4),(5 6))‘

Further reading: Collect geometries algorithm

9.2.13.18. combine

Returns the combination of two geometries.

Sintaksė

combine(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • geom_to_wkt( combine( geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 2 1)' ) ) ) → ‚MULTILINESTRING((4 4, 2 1), (3 3, 4 4), (4 4, 5 5))‘

  • geom_to_wkt( combine( geom_from_wkt( 'LINESTRING(3 3, 4 4)' ), geom_from_wkt( 'LINESTRING(3 3, 6 6, 2 1)' ) ) ) → ‚LINESTRING(3 3, 4 4, 6 6, 2 1)‘

9.2.13.19. concave_hull

Returns a possibly concave polygon that contains all the points in the geometry

Sintaksė

concave_hull(geometry, target_percent, [allow_holes=False])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • target_percent - the percentage of area of the convex hull the solution tries to approach. A target_percent of 1 gives the same result as the convex hull. A target_percent between 0 and 0.99 produces a result that should have a smaller area than the convex hull.

  • allow_holes - optional argument specifying whether to allow holes within the output geometry. Defaults to FALSE, set to TRUE to allow including holes in the output geometry.

Pavyzdžiai

  • geom_to_wkt(concave_hull(geom_from_wkt('MULTILINESTRING((106 164,30 112,74 70,82 112,130 94,130 62,122 40,156 32,162 76,172 88),(132 178,134 148,128 136,96 128,132 108,150 130,170 142,174 110,156 96,158 90,158 88),(22 64,66 28,94 38,94 68,114 76,112 30,132 10,168 18,178 34,186 52,184 74,190 100,190 122,182 148,178 170,176 184,156 164,146 178,132 186,92 182,56 158,36 150,62 150,76 128,88 118))'), 0.99)) → ‚Polygon ((30 112, 36 150, 92 182, 132 186, 176 184, 190 122, 190 100, 186 52, 178 34, 168 18, 132 10, 112 30, 66 28, 22 64, 30 112))‘

../../../_images/concave_hull_threshold.png

Fig. 9.10 Concave hulls with increasing target_percent parameter

Further reading: convex_hull, Concave hull algorithm

9.2.13.20. contains

Tests whether a geometry contains another. Returns TRUE if and only if no points of geometry2 lie in the exterior of geometry1, and at least one point of the interior of geometry2 lies in the interior of geometry1.

Sintaksė

contains(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • contains( geom_from_wkt( 'POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))' ), geom_from_wkt( 'POINT(0.5 0.5 )' ) ) → TRUE

  • contains( geom_from_wkt( 'POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → FALSE

Further reading: overlay_contains

9.2.13.21. convex_hull

Returns the convex hull of a geometry. It represents the minimum convex geometry that encloses all geometries within the set.

Sintaksė

convex_hull(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • geom_to_wkt( convex_hull( geom_from_wkt( 'LINESTRING(3 3, 4 4, 4 10)' ) ) ) → ‚POLYGON((3 3, 4 10, 4 4, 3 3))‘

../../../_images/convex_hull.png

Fig. 9.11 Black lines identify the convex hull for each feature

Further reading: concave_hull, Convex hull algorithm

9.2.13.22. crosses

Tests whether a geometry crosses another. Returns TRUE if the supplied geometries have some, but not all, interior points in common.

Sintaksė

crosses(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • crosses( geom_from_wkt( 'LINESTRING(3 5, 4 4, 5 3)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → TRUE

  • crosses( geom_from_wkt( 'POINT(4 5)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → FALSE

Further reading: overlay_crosses

9.2.13.23. densify_by_count

Takes a polygon or line layer geometry and generates a new one in which the geometries have a larger number of vertices than the original one.

Sintaksė

densify_by_count(geometry, vertices)

Argumentai

  • geometry - a geometry (accepts (multi)linestrings or (multi)polygons).

  • vertices - number of vertices to add (per segment)

Pavyzdžiai

  • geom_to_wkt(densify_by_count(geom_from_wkt('LINESTRING(1 1, 10 1)'), 3)) → LineString (1 1, 3.25 1, 5.5 1, 7.75 1, 10 1)

../../../_images/densify_geometry.png

Fig. 9.12 Red points show the vertices before and after the densify

Further reading: Densify by count algorithm

9.2.13.24. densify_by_distance

Takes a polygon or line layer geometry and generates a new one in which the geometries are densified by adding additional vertices on edges that have a maximum distance of the specified interval distance.

Sintaksė

densify_by_distance(geometry, distance)

Argumentai

  • geometry - a geometry (accepts (multi)linestrings or (multi)polygons).

  • distance - maximum interval distance between vertices in output geometry

Pavyzdžiai

  • geom_to_wkt(densify_by_distance(geom_from_wkt('LINESTRING(1 1, 10 1)'), 4)) → LineString (1 1, 4 1, 7 1, 10 1)

../../../_images/densify_geometry_interval.png

Fig. 9.13 Densify geometry at a given interval

Further reading: Densify by interval algorithm

9.2.13.25. difference

Returns a geometry that represents that part of geometry1 that does not intersect with geometry2.

Sintaksė

difference(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • geom_to_wkt( difference( geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4)' ) ) ) → ‚LINESTRING(4 4, 5 5)‘

Further reading: Skirtumas algorithm

9.2.13.26. disjoint

Tests whether geometries do not spatially intersect. Returns TRUE if the geometries do not share any space together.

Sintaksė

disjoint(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • disjoint( geom_from_wkt( 'POLYGON((0 0, 0 1, 1 1, 1 0, 0 0 ))' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → TRUE

  • disjoint( geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ), geom_from_wkt( 'POINT(4 4)' )) → FALSE

Further reading: overlay_disjoint

9.2.13.27. distance

Returns the minimum distance (based on spatial reference) between two geometries in projected units.

Sintaksė

distance(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • distance( geom_from_wkt( 'POINT(4 4)' ), geom_from_wkt( 'POINT(4 8)' ) ) → 4

9.2.13.28. distance_to_vertex

Returns the distance along the geometry to a specified vertex.

Sintaksė

distance_to_vertex(geometry, vertex)

Argumentai

  • geometry - a linestring geometry

  • vertex - vertex index, starting from 0; if the value is negative, the selected vertex index will be its total count minus the absolute value

Pavyzdžiai

  • distance_to_vertex(geometry:=geom_from_wkt('LineString(0 0, 10 0, 10 10)'),vertex:=1) → 10.0

9.2.13.29. end_point

Returns the last node from a geometry.

Sintaksė

end_point(geometry)

Argumentai

  • geometry - geometry object

Pavyzdžiai

  • geom_to_wkt(end_point(geom_from_wkt('LINESTRING(4 0, 4 2, 0 2)'))) → ‚Point (0 2)‘

../../../_images/end_point.png

Fig. 9.14 End point of a line feature

Further reading: start_point, Extract specific vertices algorithm

9.2.13.30. exif_geotag

Creates a point geometry from the exif geotags of an image file.

Sintaksė

exif_geotag(path)

Argumentai

  • path - An image file path or a map layer value. If a map layer value is specified then the file source of the layer will be used.

Pavyzdžiai

  • geom_to_wkt(exif_geotag('/my/photo.jpg')) → ‚Point (2 4)‘

9.2.13.31. extend

Extends the start and end of a linestring geometry by a specified amount. Lines are extended using the bearing of the first and last segment in the line. For a multilinestring, all the parts are extended. Distances are in the Spatial Reference System of this geometry.

Sintaksė

extend(geometry, start_distance, end_distance)

Argumentai

  • geometry - a (multi)linestring geometry

  • start_distance - distance to extend the start of the line

  • end_distance - distance to extend the end of the line.

Pavyzdžiai

  • geom_to_wkt(extend(geom_from_wkt('LineString(0 0, 1 0, 1 1)'),1,2)) → ‚LineString (-1 0, 1 0, 1 3)‘

  • geom_to_wkt(extend(geom_from_wkt('MultiLineString((0 0, 1 0, 1 1), (2 2, 0 2, 0 5))'),1,2)) → ‚MultiLineString ((-1 0, 1 0, 1 3),(3 2, 0 2, 0 7))‘

../../../_images/extend_lines.png

Fig. 9.15 The red dashes represent the initial and final extension of the original layer

Further reading: Extend lines algorithm

9.2.13.32. exterior_ring

Returns a line string representing the exterior ring of a polygon geometry. If the geometry is not a polygon then the result will be NULL.

Sintaksė

exterior_ring(geometry)

Argumentai

  • geometry - a polygon geometry

Pavyzdžiai

  • geom_to_wkt(exterior_ring(geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1),( 0.1 0.1, 0.1 0.2, 0.2 0.2, 0.2, 0.1, 0.1 0.1))'))) → ‚LineString (-1 -1, 4 0, 4 2, 0 2, -1 -1)‘

../../../_images/exterior_ring.png

Fig. 9.16 The dashed line represents the exterior ring of the polygon

9.2.13.33. extrude

Returns an extruded version of the input (Multi-)Curve or (Multi-)Linestring geometry with an extension specified by x and y.

Sintaksė

extrude(geometry, x, y)

Argumentai

  • geometry - a curve or linestring geometry

  • x - x extension, numeric value

  • y - y extension, numeric value

Pavyzdžiai

  • geom_to_wkt(extrude(geom_from_wkt('LineString(1 2, 3 2, 4 3)'), 1, 2)) → ‚Polygon ((1 2, 3 2, 4 3, 5 5, 4 4, 2 4, 1 2))‘

  • geom_to_wkt(extrude(geom_from_wkt('MultiLineString((1 2, 3 2), (4 3, 8 3))'), 1, 2)) → ‚MultiPolygon (((1 2, 3 2, 4 4, 2 4, 1 2)),((4 3, 8 3, 9 5, 5 5, 4 3)))‘

../../../_images/extrude.png

Fig. 9.17 Generating a polygon by extruding a line with offset in x and y directions

9.2.13.34. flip_coordinates

Returns a copy of the geometry with the x and y coordinates swapped. Useful for repairing geometries which have had their latitude and longitude values reversed.

Sintaksė

flip_coordinates(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • geom_to_wkt(flip_coordinates(make_point(1, 2))) → ‚Point (2 1)‘

  • geom_to_wkt(flip_coordinates(geom_from_wkt('LineString(0 2, 1 0, 1 6)'))) → ‚LineString (2 0, 0 1, 6 1)‘

Further reading: Swap X and Y coordinates algorithm

9.2.13.35. force_polygon_ccw

Forces a geometry to respect the convention where exterior rings are counter-clockwise, interior rings are clockwise.

Sintaksė

force_polygon_ccw(geometry)

Argumentai

  • geometry - a geometry. Any non-polygon geometries are returned unchanged.

Pavyzdžiai

  • geom_to_wkt(force_polygon_ccw(geometry:=geom_from_wkt('Polygon ((-1 -1, 0 2, 4 2, 4 0, -1 -1))'))) → ‚Polygon ((-1 -1, 4 0, 4 2, 0 2, -1 -1))‘

Further reading: force_polygon_cw, force_rhr

9.2.13.36. force_polygon_cw

Forces a geometry to respect the convention where exterior rings are clockwise, interior rings are counter-clockwise.

Sintaksė

force_polygon_cw(geometry)

Argumentai

  • geometry - a geometry. Any non-polygon geometries are returned unchanged.

Pavyzdžiai

  • geom_to_wkt(force_polygon_cw(geometry:=geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1))'))) → ‚Polygon ((-1 -1, 0 2, 4 2, 4 0, -1 -1))‘

Further reading: force_polygon_ccw, force_rhr

9.2.13.37. force_rhr

Forces a geometry to respect the Right-Hand-Rule, in which the area that is bounded by a polygon is to the right of the boundary. In particular, the exterior ring is oriented in a clockwise direction and the interior rings in a counter-clockwise direction. Due to the inconsistency in the definition of the Right-Hand-Rule in some contexts it is recommended to use the explicit force_polygon_cw function instead.

Sintaksė

force_rhr(geometry)

Argumentai

  • geometry - a geometry. Any non-polygon geometries are returned unchanged.

Pavyzdžiai

  • geom_to_wkt(force_rhr(geometry:=geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1))'))) → ‚Polygon ((-1 -1, 0 2, 4 2, 4 0, -1 -1))‘

Further reading: Force right-hand-rule algorithm, force_polygon_ccw, force_polygon_cw

9.2.13.38. geom_from_gml

Returns a geometry from a GML representation of geometry.

Sintaksė

geom_from_gml(gml)

Argumentai

  • gml - GML representation of a geometry as a string

Pavyzdžiai

  • geom_from_gml('<gml:LineString srsName="EPSG:4326"><gml:coordinates>4,4 5,5 6,6</gml:coordinates></gml:LineString>') → a line geometry object

9.2.13.39. geom_from_wkb

Returns a geometry created from a Well-Known Binary (WKB) representation.

Sintaksė

geom_from_wkb(binary)

Argumentai

  • binary - Well-Known Binary (WKB) representation of a geometry (as a binary blob)

Pavyzdžiai

  • geom_from_wkb( geom_to_wkb( make_point(4,5) ) ) → a point geometry object

9.2.13.40. geom_from_wkt

Returns a geometry created from a Well-Known Text (WKT) representation.

Sintaksė

geom_from_wkt(text)

Argumentai

  • text - Well-Known Text (WKT) representation of a geometry

Pavyzdžiai

  • geom_from_wkt( 'POINT(4 5)' ) → a geometry object

9.2.13.41. geom_to_wkb

Returns the Well-Known Binary (WKB) representation of a geometry

Sintaksė

geom_to_wkb(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • geom_to_wkb( @geometry ) → binary blob containing a geometry object

9.2.13.42. geom_to_wkt

Returns the Well-Known Text (WKT) representation of the geometry without SRID metadata.

Sintaksė

geom_to_wkt(geometry, [precision=8])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • precision - numeric precision

Pavyzdžiai

  • geom_to_wkt( make_point(6, 50) ) → ‚POINT(6 50)‘

  • geom_to_wkt(centroid(geom_from_wkt('Polygon((1 1, 0 0, -1 1, 1 1))'))) → ‚POINT(0 0.66666667)‘

  • geom_to_wkt(centroid(geom_from_wkt('Polygon((1 1, 0 0, -1 1, 1 1))')), 2) → ‚POINT(0 0.67)‘

9.2.13.43. $geometry

Returns the geometry of the current feature. Can be used for processing with other functions. WARNING: This function is deprecated. It is recommended to use the replacement @geometry variable instead.

Sintaksė

$geometry

Pavyzdžiai

  • geom_to_wkt( $geometry ) → ‚POINT(6 50)‘

9.2.13.44. geometry

Returns a feature’s geometry.

Sintaksė

geometry(feature)

Argumentai

  • feature - a feature object

Pavyzdžiai

  • geometry( @feature ) → the geometry of the current feature. Prefer using @geometry.

  • geom_to_wkt( geometry( get_feature_by_id( 'streets', 1 ) ) ) → the geometry in WKT of the feature with the id 1 on the layer „streets“, e.g. ‚POINT(6 50)‘

  • intersects( @geometry, geometry( get_feature( 'streets', 'name', 'Main St.' ) ) ) → TRUE if the current feature spatially intersects the ‚Main St.‘ named feature in the „streets“ layer

9.2.13.45. geometry_n

Returns a specific geometry from a geometry collection, or NULL if the input geometry is not a collection. Also returns a part from a multipart geometry.

Sintaksė

geometry_n(geometry, index)

Argumentai

  • geometry - geometry collection

  • index - index of geometry to return, where 1 is the first geometry in the collection

Pavyzdžiai

  • geom_to_wkt(geometry_n(geom_from_wkt('GEOMETRYCOLLECTION(POINT(0 1), POINT(0 0), POINT(1 0), POINT(1 1))'),3)) → ‚Point (1 0)‘

9.2.13.46. geometry_type

Returns a string value describing the type of a geometry (Point, Line or Polygon)

Sintaksė

geometry_type(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • geometry_type( geom_from_wkt( 'LINESTRING(2 5, 3 6, 4 8)') ) → ‚Line‘

  • geometry_type( geom_from_wkt( 'MULTILINESTRING((2 5, 3 6, 4 8), (1 1, 0 0))') ) → ‚Line‘

  • geometry_type( geom_from_wkt( 'POINT(2 5)') ) → ‚Point‘

  • geometry_type( geom_from_wkt( 'POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1))') ) → ‚Polygon‘

9.2.13.47. hausdorff_distance

Returns the Hausdorff distance between two geometries. This is basically a measure of how similar or dissimilar 2 geometries are, with a lower distance indicating more similar geometries.

The function can be executed with an optional densify fraction argument. If not specified, an approximation to the standard Hausdorff distance is used. This approximation is exact or close enough for a large subset of useful cases. Examples of these are:

  • computing distance between Linestrings that are roughly parallel to each other, and roughly equal in length. This occurs in matching linear networks.

  • Testing similarity of geometries.

If the default approximate provided by this method is insufficient, specify the optional densify fraction argument. Specifying this argument performs a segment densification before computing the discrete Hausdorff distance. The parameter sets the fraction by which to densify each segment. Each segment will be split into a number of equal-length subsegments, whose fraction of the total length is closest to the given fraction. Decreasing the densify fraction parameter will make the distance returned approach the true Hausdorff distance for the geometries.

Sintaksė

hausdorff_distance(geometry1, geometry2, [densify_fraction])

[] žymi neprivalomus argumentus

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

  • densify_fraction - densify fraction amount

Pavyzdžiai

  • hausdorff_distance( geometry1:= geom_from_wkt('LINESTRING (0 0, 2 1)'),geometry2:=geom_from_wkt('LINESTRING (0 0, 2 0)')) → 2

  • hausdorff_distance( geom_from_wkt('LINESTRING (130 0, 0 0, 0 150)'),geom_from_wkt('LINESTRING (10 10, 10 150, 130 10)')) → 14.142135623

  • hausdorff_distance( geom_from_wkt('LINESTRING (130 0, 0 0, 0 150)'),geom_from_wkt('LINESTRING (10 10, 10 150, 130 10)'),0.5) → 70.0

9.2.13.48. inclination

Returns the inclination measured from the zenith (0) to the nadir (180) on point_a to point_b.

Sintaksė

inclination(point_a, point_b)

Argumentai

  • point_a - point geometry

  • point_b - point geometry

Pavyzdžiai

  • inclination( make_point( 5, 10, 0 ), make_point( 5, 10, 5 ) ) → 0.0

  • inclination( make_point( 5, 10, 0 ), make_point( 5, 10, 0 ) ) → 90.0

  • inclination( make_point( 5, 10, 0 ), make_point( 50, 100, 0 ) ) → 90.0

  • inclination( make_point( 5, 10, 0 ), make_point( 5, 10, -5 ) ) → 180.0

9.2.13.49. interior_ring_n

Returns a specific interior ring from a polygon geometry, or NULL if the geometry is not a polygon.

Sintaksė

interior_ring_n(geometry, index)

Argumentai

  • geometry - polygon geometry

  • index - index of interior to return, where 1 is the first interior ring

Pavyzdžiai

  • geom_to_wkt(interior_ring_n(geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1),(-0.1 -0.1, 0.4 0, 0.4 0.2, 0 0.2, -0.1 -0.1),(-1 -1, 4 0, 4 2, 0 2, -1 -1))'),1)) → ‚LineString (-0.1 -0.1, 0.4 0, 0.4 0.2, 0 0.2, -0.1 -0.1))‘

9.2.13.50. intersection

Returns a geometry that represents the shared portion of two geometries.

Sintaksė

intersection(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • geom_to_wkt( intersection( geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4)' ) ) ) → ‚LINESTRING(3 3, 4 4)‘

  • geom_to_wkt( intersection( geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ), geom_from_wkt( 'MULTIPOINT(3.5 3.5, 4 5)' ) ) ) → ‚POINT(3.5 3.5)‘

Further reading: Intersection algorithm

9.2.13.51. intersects

Tests whether a geometry intersects another. Returns TRUE if the geometries spatially intersect (share any portion of space) and false if they do not.

Sintaksė

intersects(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • intersects( geom_from_wkt( 'POINT(4 4)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → TRUE

  • intersects( geom_from_wkt( 'POINT(4 5)' ), geom_from_wkt( 'POINT(5 5)' ) ) → FALSE

Further reading: overlay_intersects

9.2.13.52. intersects_bbox

Tests whether a geometry’s bounding box overlaps another geometry’s bounding box. Returns TRUE if the geometries spatially intersect the bounding box defined and false if they do not.

Sintaksė

intersects_bbox(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • intersects_bbox( geom_from_wkt( 'POINT(4 5)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → TRUE

  • intersects_bbox( geom_from_wkt( 'POINT(6 5)' ), geom_from_wkt( 'POLYGON((3 3, 4 4, 5 5, 3 3))' ) ) → FALSE

9.2.13.53. is_closed

Returns TRUE if a line string is closed (start and end points are coincident), or false if a line string is not closed. If the geometry is not a line string then the result will be NULL.

Sintaksė

is_closed(geometry)

Argumentai

  • geometry - a line string geometry

Pavyzdžiai

  • is_closed(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2)')) → FALSE

  • is_closed(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2, 0 0)')) → TRUE

9.2.13.54. is_empty

Returns TRUE if a geometry is empty (without coordinates), false if the geometry is not empty and NULL if there is no geometry. See also is_empty_or_null.

Sintaksė

is_empty(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • is_empty(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2)')) → FALSE

  • is_empty(geom_from_wkt('LINESTRING EMPTY')) → TRUE

  • is_empty(geom_from_wkt('POINT(7 4)')) → FALSE

  • is_empty(geom_from_wkt('POINT EMPTY')) → TRUE

Further reading: is_empty_or_null

9.2.13.55. is_empty_or_null

Returns TRUE if a geometry is NULL or empty (without coordinates) or false otherwise. This function is like the expression @geometry IS NULL or is_empty(@geometry)‘

Sintaksė

is_empty_or_null(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • is_empty_or_null(NULL) → TRUE

  • is_empty_or_null(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2)')) → FALSE

  • is_empty_or_null(geom_from_wkt('LINESTRING EMPTY')) → TRUE

  • is_empty_or_null(geom_from_wkt('POINT(7 4)')) → FALSE

  • is_empty_or_null(geom_from_wkt('POINT EMPTY')) → TRUE

Further reading: is_empty, NULL

9.2.13.56. is_multipart

Returns TRUE if the geometry is of Multi type.

Sintaksė

is_multipart(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • is_multipart(geom_from_wkt('MULTIPOINT ((0 0),(1 1),(2 2))')) → TRUE

  • is_multipart(geom_from_wkt('POINT (0 0)')) → FALSE

9.2.13.57. is_valid

Returns TRUE if a geometry is valid; if it is well-formed in 2D according to the OGC rules.

Sintaksė

is_valid(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • is_valid(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2, 0 0)')) → TRUE

  • is_valid(geom_from_wkt('LINESTRING(0 0)')) → FALSE

Further reading: make_valid, Check validity algorithm

9.2.13.58. $length

Returns the length of a linestring. If you need the length of a border of a polygon, use $perimeter instead. The length calculated by this function respects both the current project’s ellipsoid setting and distance unit settings. For example, if an ellipsoid has been set for the project then the calculated length will be ellipsoidal, and if no ellipsoid is set then the calculated length will be planimetric.

Sintaksė

$length

Pavyzdžiai

  • $length → 42.4711

9.2.13.59. length

Returns the number of characters in a string or the length of a geometry linestring.

String variant

Returns the number of characters in a string.

Sintaksė

length(string)

Argumentai

  • string - string to count length of

Pavyzdžiai

  • length('hello') → 5

Geometry variant

Calculate the length of a geometry line object. Calculations are always planimetric in the Spatial Reference System (SRS) of this geometry, and the units of the returned length will match the units for the SRS. This differs from the calculations performed by the $length function, which will perform ellipsoidal calculations based on the project’s ellipsoid and distance unit settings.

Sintaksė

length(geometry)

Argumentai

  • geometry - line geometry object

Pavyzdžiai

  • length(geom_from_wkt('LINESTRING(0 0, 4 0)')) → 4.0

Further reading: straight_distance_2d

9.2.13.60. length3D

Calculates the 3D length of a geometry line object. If the geometry is not a 3D line object, it returns its 2D length. Calculations are always planimetric in the Spatial Reference System (SRS) of this geometry, and the units of the returned length will match the units for the SRS. This differs from the calculations performed by the $length function, which will perform ellipsoidal calculations based on the project’s ellipsoid and distance unit settings.

Sintaksė

length3D(geometry)

Argumentai

  • geometry - line geometry object

Pavyzdžiai

  • length3D(geom_from_wkt('LINESTRINGZ(0 0 0, 3 0 4)')) → 5.0

9.2.13.61. line_interpolate_angle

Returns the angle parallel to the geometry at a specified distance along a linestring geometry. Angles are in degrees clockwise from north.

Sintaksė

line_interpolate_angle(geometry, distance)

Argumentai

  • geometry - a linestring geometry

  • distance - distance along line to interpolate angle at

Pavyzdžiai

  • line_interpolate_angle(geometry:=geom_from_wkt('LineString(0 0, 10 0)'),distance:=5) → 90.0

9.2.13.62. line_interpolate_point

Returns the point interpolated by a specified distance along a linestring geometry.

Sintaksė

line_interpolate_point(geometry, distance)

Argumentai

  • geometry - a linestring geometry

  • distance - distance along line to interpolate

Pavyzdžiai

  • geom_to_wkt(line_interpolate_point(geometry:=geom_from_wkt('LineString(0 0, 8 0)'), distance:=5)) → ‚Point (5 0)‘

  • geom_to_wkt(line_interpolate_point(geometry:=geom_from_wkt('LineString(0 0, 1 1, 2 0)'), distance:=2.1)) → ‚Point (1.48492424 0.51507576)‘

  • geom_to_wkt(line_interpolate_point(geometry:=geom_from_wkt('LineString(0 0, 1 0)'), distance:=2)) → NULL

../../../_images/interpolated_point.png

Fig. 9.18 Interpolated point at 500m of the beginning of the line

Further reading: Interpolate point on line algorithm

9.2.13.63. line_interpolate_point_by_m

Returns the point interpolated by a matching M value along a linestring geometry.

Sintaksė

line_interpolate_point_by_m(geometry, m, [use_3d_distance=false])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a linestring geometry

  • m - an M value

  • use_3d_distance - controls whether 2D or 3D distances between vertices should be used during interpolation (this option is only considered for lines with z values)

Pavyzdžiai

  • geom_to_wkt(line_interpolate_point_by_m(geom_from_wkt('LineStringM(0 0 0, 10 10 10)'), m:=5)) → ‚Point (5 5)‘

9.2.13.64. line_locate_m

Returns the distance along a linestring corresponding to the first matching interpolated M value.

Sintaksė

line_locate_m(geometry, m, [use_3d_distance=false])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a linestring geometry

  • m - an M value

  • use_3d_distance - controls whether 2D or 3D distances between vertices should be used during interpolation (this option is only considered for lines with z values)

Pavyzdžiai

  • line_locate_m(geometry:=geom_from_wkt('LineStringM(0 0 0, 10 10 10)'),m:=5) → 7.07106

9.2.13.65. line_locate_point

Returns the distance along a linestring corresponding to the closest position the linestring comes to a specified point geometry.

Sintaksė

line_locate_point(geometry, point)

Argumentai

  • geometry - a linestring geometry

  • point - point geometry to locate closest position on linestring to

Pavyzdžiai

  • line_locate_point(geometry:=geom_from_wkt('LineString(0 0, 10 0)'),point:=geom_from_wkt('Point(5 0)')) → 5.0

9.2.13.66. line_merge

Returns a LineString or MultiLineString geometry, where any connected LineStrings from the input geometry have been merged into a single linestring. This function will return NULL if passed a geometry which is not a LineString/MultiLineString.

Sintaksė

line_merge(geometry)

Argumentai

  • geometry - a LineString/MultiLineString geometry

Pavyzdžiai

  • geom_to_wkt(line_merge(geom_from_wkt('MULTILINESTRING((0 0, 1 1),(1 1, 2 2))'))) → ‚LineString(0 0,1 1,2 2)‘

  • geom_to_wkt(line_merge(geom_from_wkt('MULTILINESTRING((0 0, 1 1),(11 1, 21 2))'))) → ‚MultiLineString((0 0, 1 1),(11 1, 21 2)‘

9.2.13.67. line_substring

Returns the portion of a line (or curve) geometry which falls between the specified start and end distances (measured from the beginning of the line). Z and M values are linearly interpolated from existing values.

Sintaksė

line_substring(geometry, start_distance, end_distance)

Argumentai

  • geometry - a linestring or curve geometry

  • start_distance - distance to start of substring

  • end_distance - distance to end of substring

Pavyzdžiai

  • geom_to_wkt(line_substring(geometry:=geom_from_wkt('LineString(0 0, 10 0)'),start_distance:=2,end_distance:=6)) → ‚LineString (2 0,6 0)‘

../../../_images/substring.png

Fig. 9.19 Substring line with starting distance set at 0 meters and the ending distance at 250 meters.

Further reading: Line substring algorithm

9.2.13.68. m

Returns the m (measure) value of a point geometry.

Sintaksė

m(geometry)

Argumentai

  • geometry - a point geometry

Pavyzdžiai

  • m( geom_from_wkt( 'POINTM(2 5 4)' ) ) → 4

9.2.13.69. m_at

Retrieves a m coordinate of the geometry, or NULL if the geometry has no m value.

Sintaksė

m_at(geometry, vertex)

Argumentai

  • geometry - geometry object

  • vertex - index of the vertex of the geometry (indices start at 0; negative values apply from the last index, starting at -1)

Pavyzdžiai

  • m_at(geom_from_wkt('LineStringZM(0 0 0 0, 10 10 0 5, 10 10 0 0)'), 1) → 5

9.2.13.70. m_max

Returns the maximum m (measure) value of a geometry.

Sintaksė

m_max(geometry)

Argumentai

  • geometry - a geometry containing m values

Pavyzdžiai

  • m_max( make_point_m( 0,0,1 ) ) → 1

  • m_max(make_line( make_point_m( 0,0,1 ), make_point_m( -1,-1,2 ), make_point_m( -2,-2,0 ) ) ) → 2

9.2.13.71. m_min

Returns the minimum m (measure) value of a geometry.

Sintaksė

m_min(geometry)

Argumentai

  • geometry - a geometry containing m values

Pavyzdžiai

  • m_min( make_point_m( 0,0,1 ) ) → 1

  • m_min(make_line( make_point_m( 0,0,1 ), make_point_m( -1,-1,2 ), make_point_m( -2,-2,0 ) ) ) → 0

9.2.13.72. main_angle

Returns the angle of the long axis (clockwise, in degrees from North) of the oriented minimal bounding rectangle, which completely covers the geometry.

Sintaksė

main_angle(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • main_angle(geom_from_wkt('Polygon ((321577 129614, 321581 129618, 321585 129615, 321581 129610, 321577 129614))')) → 38.66

9.2.13.73. make_circle

Creates a circular polygon.

Sintaksė

make_circle(center, radius, [segments=36])

[] žymi neprivalomus argumentus

Argumentai

  • center - center point of the circle

  • radius - radius of the circle

  • segments - optional argument for polygon segmentation. By default this value is 36

Pavyzdžiai

  • geom_to_wkt(make_circle(make_point(10,10), 5, 4)) → ‚Polygon ((10 15, 15 10, 10 5, 5 10, 10 15))‘

  • geom_to_wkt(make_circle(make_point(10,10,5), 5, 4)) → ‚PolygonZ ((10 15 5, 15 10 5, 10 5 5, 5 10 5, 10 15 5))‘

  • geom_to_wkt(make_circle(make_point(10,10,5,30), 5, 4)) → ‚PolygonZM ((10 15 5 30, 15 10 5 30, 10 5 5 30, 5 10 5 30, 10 15 5 30))‘

9.2.13.74. make_ellipse

Creates an elliptical polygon.

Sintaksė

make_ellipse(center, semi_major_axis, semi_minor_axis, azimuth, [segments=36])

[] žymi neprivalomus argumentus

Argumentai

  • center - center point of the ellipse

  • semi_major_axis - semi-major axis of the ellipse

  • semi_minor_axis - semi-minor axis of the ellipse

  • azimuth - orientation of the ellipse

  • segments - optional argument for polygon segmentation. By default this value is 36

Pavyzdžiai

  • geom_to_wkt(make_ellipse(make_point(10,10), 5, 2, 90, 4)) → ‚Polygon ((15 10, 10 8, 5 10, 10 12, 15 10))‘

  • geom_to_wkt(make_ellipse(make_point(10,10,5), 5, 2, 90, 4)) → ‚PolygonZ ((15 10 5, 10 8 5, 5 10 5, 10 12 5, 15 10 5))‘

  • geom_to_wkt(make_ellipse(make_point(10,10,5,30), 5, 2, 90, 4)) → ‚PolygonZM ((15 10 5 30, 10 8 5 30, 5 10 5 30, 10 12 5 30, 15 10 5 30))‘

9.2.13.75. make_line

Creates a line geometry from a series of point geometries.

List of arguments variant

Line vertices are specified as separate arguments to the function.

Sintaksė

make_line(point1, point2, …)

Argumentai

  • point - a point geometry (or array of points)

Pavyzdžiai

  • geom_to_wkt(make_line(make_point(2,4),make_point(3,5))) → ‚LineString (2 4, 3 5)‘

  • geom_to_wkt(make_line(make_point(2,4),make_point(3,5),make_point(9,7))) → ‚LineString (2 4, 3 5, 9 7)‘

Array variant

Line vertices are specified as an array of points.

Sintaksė

make_line(array)

Argumentai

  • array - array of points

Pavyzdžiai

  • geom_to_wkt(make_line(array(make_point(2,4),make_point(3,5),make_point(9,7)))) → ‚LineString (2 4, 3 5, 9 7)‘

9.2.13.76. make_point

Creates a point geometry from an x and y (and optional z and m) value.

Sintaksė

make_point(x, y, [z], [m])

[] žymi neprivalomus argumentus

Argumentai

  • x - x coordinate of point

  • y - y coordinate of point

  • z - optional z coordinate of point

  • m - optional m value of point

Pavyzdžiai

  • geom_to_wkt(make_point(2,4)) → ‚Point (2 4)‘

  • geom_to_wkt(make_point(2,4,6)) → ‚PointZ (2 4 6)‘

  • geom_to_wkt(make_point(2,4,6,8)) → ‚PointZM (2 4 6 8)‘

9.2.13.77. make_point_m

Creates a point geometry from an x, y coordinate and m value.

Sintaksė

make_point_m(x, y, m)

Argumentai

  • x - x coordinate of point

  • y - y coordinate of point

  • m - m value of point

Pavyzdžiai

  • geom_to_wkt(make_point_m(2,4,6)) → ‚PointM (2 4 6)‘

9.2.13.78. make_polygon

Creates a polygon geometry from an outer ring and optional series of inner ring geometries.

Sintaksė

make_polygon(outerRing, [innerRing1], [innerRing2], …)

[] žymi neprivalomus argumentus

Argumentai

  • outerRing - closed line geometry for polygon’s outer ring

  • innerRing - optional closed line geometry for inner ring

Pavyzdžiai

  • geom_to_wkt(make_polygon(geom_from_wkt('LINESTRING( 0 0, 0 1, 1 1, 1 0, 0 0 )'))) → ‚Polygon ((0 0, 0 1, 1 1, 1 0, 0 0))‘

  • geom_to_wkt(make_polygon(geom_from_wkt('LINESTRING( 0 0, 0 1, 1 1, 1 0, 0 0 )'),geom_from_wkt('LINESTRING( 0.1 0.1, 0.1 0.2, 0.2 0.2, 0.2 0.1, 0.1 0.1 )'),geom_from_wkt('LINESTRING( 0.8 0.8, 0.8 0.9, 0.9 0.9, 0.9 0.8, 0.8 0.8 )'))) → ‚Polygon ((0 0, 0 1, 1 1, 1 0, 0 0),(0.1 0.1, 0.1 0.2, 0.2 0.2, 0.2 0.1, 0.1 0.1),(0.8 0.8, 0.8 0.9, 0.9 0.9, 0.9 0.8, 0.8 0.8))‘

9.2.13.79. make_rectangle_3points

Creates a rectangle from 3 points.

Sintaksė

make_rectangle_3points(point1, point2, point3, [option=0])

[] žymi neprivalomus argumentus

Argumentai

  • point1 - First point.

  • point2 - Second point.

  • point3 - Third point.

  • option - An optional argument to construct the rectangle. By default this value is 0. Value can be 0 (distance) or 1 (projected). Option distance: Second distance is equal to the distance between 2nd and 3rd point. Option projected: Second distance is equal to the distance of the perpendicular projection of the 3rd point on the segment or its extension.

Pavyzdžiai

  • geom_to_wkt(make_rectangle_3points(make_point(0, 0), make_point(0,5), make_point(5, 5), 0)) → ‚Polygon ((0 0, 0 5, 5 5, 5 0, 0 0))‘

  • geom_to_wkt(make_rectangle_3points(make_point(0, 0), make_point(0,5), make_point(5, 3), 1)) → ‚Polygon ((0 0, 0 5, 5 5, 5 0, 0 0))‘

9.2.13.80. make_regular_polygon

Creates a regular polygon.

Sintaksė

make_regular_polygon(center, radius, number_sides, [circle=0])

[] žymi neprivalomus argumentus

Argumentai

  • center - center of the regular polygon

  • radius - second point. The first if the regular polygon is inscribed. The midpoint of the first side if the regular polygon is circumscribed.

  • number_sides - Number of sides/edges of the regular polygon

  • circle - Optional argument to construct the regular polygon. By default this value is 0. Value can be 0 (inscribed) or 1 (circumscribed)

Pavyzdžiai

  • geom_to_wkt(make_regular_polygon(make_point(0,0), make_point(0,5), 5)) → ‚Polygon ((0 5, 4.76 1.55, 2.94 -4.05, -2.94 -4.05, -4.76 1.55, 0 5))‘

  • geom_to_wkt(make_regular_polygon(make_point(0,0), project(make_point(0,0), 4.0451, radians(36)), 5)) → ‚Polygon ((0 5, 4.76 1.55, 2.94 -4.05, -2.94 -4.05, -4.76 1.55, 0 5))‘

9.2.13.81. make_square

Creates a square from a diagonal.

Sintaksė

make_square(point1, point2)

Argumentai

  • point1 - First point of the diagonal

  • point2 - Last point of the diagonal

Pavyzdžiai

  • geom_to_wkt(make_square( make_point(0,0), make_point(5,5))) → ‚Polygon ((0 0, -0 5, 5 5, 5 0, 0 0))‘

  • geom_to_wkt(make_square( make_point(5,0), make_point(5,5))) → ‚Polygon ((5 0, 2.5 2.5, 5 5, 7.5 2.5, 5 0))‘

9.2.13.82. make_triangle

Creates a triangle polygon.

Sintaksė

make_triangle(point1, point2, point3)

Argumentai

  • point1 - first point of the triangle

  • point2 - second point of the triangle

  • point3 - third point of the triangle

Pavyzdžiai

  • geom_to_wkt(make_triangle(make_point(0,0), make_point(5,5), make_point(0,10))) → ‚Triangle ((0 0, 5 5, 0 10, 0 0))‘

  • geom_to_wkt(boundary(make_triangle(make_point(0,0), make_point(5,5), make_point(0,10)))) → ‚LineString (0 0, 5 5, 0 10, 0 0)‘

9.2.13.83. make_valid

Returns a valid geometry or an empty geometry if the geometry could not be made valid.

Sintaksė

make_valid(geometry, [method=structure], [keep_collapsed=false])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • method - repair algorithm. May be either ‚structure‘ or ‚linework‘. The ‚linework‘ option combines all rings into a set of noded lines and then extracts valid polygons from that linework. The ‚structure‘ method first makes all rings valid and then merges shells and subtracts holes from shells to generate valid result. Assumes that holes and shells are correctly categorized.

  • keep_collapsed - if set to true, then components that have collapsed into a lower dimensionality will be kept. For example, a ring collapsing to a line, or a line collapsing to a point.

Pavyzdžiai

  • geom_to_wkt(make_valid(geom_from_wkt('POLYGON((3 2, 4 1, 5 8, 3 2, 4 2))'))) → ‚Polygon ((3 2, 5 8, 4 1, 3 2))‘

  • geom_to_wkt(make_valid(geom_from_wkt('POLYGON((3 2, 4 1, 5 8, 3 2, 4 2))'), 'linework')) → ‚GeometryCollection (Polygon ((5 8, 4 1, 3 2, 5 8)),LineString (3 2, 4 2))‘

  • geom_to_wkt(make_valid(geom_from_wkt('POLYGON((3 2, 4 1, 5 8))'), method:='linework')) → ‚Polygon ((3 2, 4 1, 5 8, 3 2))‘

  • make_valid(geom_from_wkt('LINESTRING(0 0)')) → An empty geometry

Further reading: is_valid, Fix geometries algorithm

9.2.13.84. minimal_circle

Returns the minimal enclosing circle of a geometry. It represents the minimum circle that encloses all geometries within the set.

Sintaksė

minimal_circle(geometry, [segments=36])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • segments - optional argument for polygon segmentation. By default this value is 36

Pavyzdžiai

  • geom_to_wkt( minimal_circle( geom_from_wkt( 'LINESTRING(0 5, 0 -5, 2 1)' ), 4 ) ) → ‚Polygon ((0 5, 5 -0, -0 -5, -5 0, 0 5))‘

  • geom_to_wkt( minimal_circle( geom_from_wkt( 'MULTIPOINT(1 2, 3 4, 3 2)' ), 4 ) ) → ‚Polygon ((3 4, 3 2, 1 2, 1 4, 3 4))‘

../../../_images/minimum_enclosing_circles.png

Fig. 9.20 Minimal enclosing circle of each feature

Further reading: Minimum enclosing circles algorithm

9.2.13.85. nodes_to_points

Returns a multipoint geometry consisting of every node in the input geometry.

Sintaksė

nodes_to_points(geometry, [ignore_closing_nodes=false])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - geometry object

  • ignore_closing_nodes - optional argument specifying whether to include duplicate nodes which close lines or polygons rings. Defaults to false, set to true to avoid including these duplicate nodes in the output collection.

Pavyzdžiai

  • geom_to_wkt(nodes_to_points(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2)'))) → ‚MultiPoint ((0 0),(1 1),(2 2))‘

  • geom_to_wkt(nodes_to_points(geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1))'),true)) → ‚MultiPoint ((-1 -1),(4 0),(4 2),(0 2))‘

../../../_images/extract_nodes.png

Fig. 9.21 Multi-point feature extracted from vertices

Further reading: Extract vertices algorithm

9.2.13.86. num_geometries

Returns the number of geometries in a geometry collection, or the number of parts in a multi-part geometry. The function returns NULL if the input geometry is not a collection.

Sintaksė

num_geometries(geometry)

Argumentai

  • geometry - geometry collection or multi-part geometry

Pavyzdžiai

  • num_geometries(geom_from_wkt('GEOMETRYCOLLECTION(POINT(0 1), POINT(0 0), POINT(1 0), POINT(1 1))')) → 4

  • num_geometries(geom_from_wkt('MULTIPOINT((0 1), (0 0), (1 0))')) → 3

9.2.13.87. num_interior_rings

Returns the number of interior rings in a polygon or geometry collection, or NULL if the input geometry is not a polygon or collection.

Sintaksė

num_interior_rings(geometry)

Argumentai

  • geometry - input geometry

Pavyzdžiai

  • num_interior_rings(geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1),(-0.1 -0.1, 0.4 0, 0.4 0.2, 0 0.2, -0.1 -0.1))')) → 1

9.2.13.88. num_points

Returns the number of vertices in a geometry.

Sintaksė

num_points(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • num_points(@geometry) → number of vertices in the current feature’s geometry

9.2.13.89. num_rings

Returns the number of rings (including exterior rings) in a polygon or geometry collection, or NULL if the input geometry is not a polygon or collection.

Sintaksė

num_rings(geometry)

Argumentai

  • geometry - input geometry

Pavyzdžiai

  • num_rings(geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1),(-0.1 -0.1, 0.4 0, 0.4 0.2, 0 0.2, -0.1 -0.1))')) → 2

9.2.13.90. offset_curve

Returns a geometry formed by offsetting a linestring geometry to the side. Distances are in the Spatial Reference System of this geometry.

Sintaksė

offset_curve(geometry, distance, [segments=8], [join=1], [miter_limit=2.0])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a (multi)linestring geometry

  • distance - offset distance. Positive values will be buffered to the left of lines, negative values to the right

  • segments - number of segments to use to represent a quarter circle when a round join style is used. A larger number results in a smoother line with more nodes.

  • join - join style for corners, where 1 = round, 2 = miter and 3 = bevel

  • miter_limit - limit on the miter ratio used for very sharp corners (when using miter joins only)

Pavyzdžiai

  • offset_curve(@geometry, 10.5) → line offset to the left by 10.5 units

  • offset_curve(@geometry, -10.5) → line offset to the right by 10.5 units

  • offset_curve(@geometry, 10.5, segments:=16, join:=1) → line offset to the left by 10.5 units, using more segments to result in a smoother curve

  • offset_curve(@geometry, 10.5, join:=3) → line offset to the left by 10.5 units, using a beveled join

../../../_images/offset_lines.png

Fig. 9.22 Mėlynas - pradinis sluoksnis, raudonas - paslinktasis

Further reading: Offset lines algorithm

9.2.13.91. order_parts

Orders the parts of a MultiGeometry by a given criteria

Sintaksė

order_parts(geometry, orderby, [ascending=true])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a multi-type geometry

  • orderby - an expression string defining the order criteria

  • ascending - boolean, True for ascending, False for descending

Pavyzdžiai

  • geom_to_wkt(order_parts(geom_from_wkt('MultiPolygon (((1 1, 5 1, 5 5, 1 5, 1 1)),((1 1, 9 1, 9 9, 1 9, 1 1)))'), 'area(@geometry)', False)) → ‚MultiPolygon (((1 1, 9 1, 9 9, 1 9, 1 1)),((1 1, 5 1, 5 5, 1 5, 1 1)))‘

  • geom_to_wkt(order_parts(geom_from_wkt('LineString(1 2, 3 2, 4 3)'), '1', True)) → ‚LineString(1 2, 3 2, 4 3)‘

9.2.13.92. oriented_bbox

Returns a geometry which represents the minimal oriented bounding box of an input geometry.

Sintaksė

oriented_bbox(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • geom_to_wkt( oriented_bbox( geom_from_wkt( 'MULTIPOINT(1 2, 3 4, 3 2)' ) ) ) → ‚Polygon ((3 2, 3 4, 1 4, 1 2, 3 2))‘

../../../_images/oriented_minimum_bounding_box.png

Fig. 9.23 Oriented minimum bounding box

Further reading: Oriented minimum bounding box algorithm

9.2.13.93. overlaps

Tests whether a geometry overlaps another. Returns TRUE if the geometries share space, are of the same dimension, but are not completely contained by each other.

Sintaksė

overlaps(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • overlaps( geom_from_wkt( 'LINESTRING(3 5, 4 4, 5 5, 5 3)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → TRUE

  • overlaps( geom_from_wkt( 'LINESTRING(0 0, 1 1)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → FALSE

9.2.13.94. overlay_contains

Returns whether the current feature spatially contains at least one feature from a target layer, or an array of expression-based results for the features in the target layer contained in the current feature.

Read more on the underlying GEOS „Contains“ predicate, as described in PostGIS ST_Contains function.

Sintaksė

overlay_contains(layer, [expression], [filter], [limit], [cache=false])

[] žymi neprivalomus argumentus

Argumentai

  • layer - the layer whose overlay is checked

  • expression - an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.

  • filter - an optional expression to filter the target features to check. If not set, all the features will be checked.

  • limit - an optional integer to limit the number of matching features. If not set, all the matching features will be returned.

  • cache - set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)

Pavyzdžiai

  • overlay_contains('regions') → TRUE if the current feature spatially contains a region

  • overlay_contains('regions', filter:= population > 10000) → TRUE if the current feature spatially contains a region with a population greater than 10000

  • overlay_contains('regions', name) → an array of names, for the regions contained in the current feature

  • array_to_string(overlay_contains('regions', name)) → a string as a comma separated list of names, for the regions contained in the current feature

  • array_sort(overlay_contains(layer:='regions', expression:="name", filter:= population > 10000)) → an ordered array of names, for the regions contained in the current feature and with a population greater than 10000

  • overlay_contains(layer:='regions', expression:= geom_to_wkt(@geometry), limit:=2) → an array of geometries (in WKT), for up to two regions contained in the current feature

Further reading: contains, array manipulation, Select by location algorithm

9.2.13.95. overlay_crosses

Returns whether the current feature spatially crosses at least one feature from a target layer, or an array of expression-based results for the features in the target layer crossed by the current feature.

Read more on the underlying GEOS „Crosses“ predicate, as described in PostGIS ST_Crosses function.

Sintaksė

overlay_crosses(layer, [expression], [filter], [limit], [cache=false])

[] žymi neprivalomus argumentus

Argumentai

  • layer - the layer whose overlay is checked

  • expression - an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.

  • filter - an optional expression to filter the target features to check. If not set, all the features will be checked.

  • limit - an optional integer to limit the number of matching features. If not set, all the matching features will be returned.

  • cache - set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)

Pavyzdžiai

  • overlay_crosses('regions') → TRUE if the current feature spatially crosses a region

  • overlay_crosses('regions', filter:= population > 10000) → TRUE if the current feature spatially crosses a region with a population greater than 10000

  • overlay_crosses('regions', name) → an array of names, for the regions crossed by the current feature

  • array_to_string(overlay_crosses('regions', name)) → a string as a comma separated list of names, for the regions crossed by the current feature

  • array_sort(overlay_crosses(layer:='regions', expression:="name", filter:= population > 10000)) → an ordered array of names, for the regions crossed by the current feature and with a population greater than 10000

  • overlay_crosses(layer:='regions', expression:= geom_to_wkt(@geometry), limit:=2) → an array of geometries (in WKT), for up to two regions crossed by the current feature

Further reading: crosses, array manipulation, Select by location algorithm

9.2.13.96. overlay_disjoint

Returns whether the current feature is spatially disjoint from all the features of a target layer, or an array of expression-based results for the features in the target layer that are disjoint from the current feature.

Read more on the underlying GEOS „Disjoint“ predicate, as described in PostGIS ST_Disjoint function.

Sintaksė

overlay_disjoint(layer, [expression], [filter], [limit], [cache=false])

[] žymi neprivalomus argumentus

Argumentai

  • layer - the layer whose overlay is checked

  • expression - an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.

  • filter - an optional expression to filter the target features to check. If not set, all the features will be checked.

  • limit - an optional integer to limit the number of matching features. If not set, all the matching features will be returned.

  • cache - set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)

Pavyzdžiai

  • overlay_disjoint('regions') → TRUE if the current feature is spatially disjoint from all the regions

  • overlay_disjoint('regions', filter:= population > 10000) → TRUE if the current feature is spatially disjoint from all the regions with a population greater than 10000

  • overlay_disjoint('regions', name) → an array of names, for the regions spatially disjoint from the current feature

  • array_to_string(overlay_disjoint('regions', name)) → a string as a comma separated list of names, for the regions spatially disjoint from the current feature

  • array_sort(overlay_disjoint(layer:='regions', expression:="name", filter:= population > 10000)) → an ordered array of names, for the regions spatially disjoint from the current feature and with a population greater than 10000

  • overlay_disjoint(layer:='regions', expression:= geom_to_wkt(@geometry), limit:=2) → an array of geometries (in WKT), for up to two regions spatially disjoint from the current feature

Further reading: disjoint, array manipulation, Select by location algorithm

9.2.13.97. overlay_equals

Returns whether the current feature spatially equals to at least one feature from a target layer, or an array of expression-based results for the features in the target layer that are spatially equal to the current feature.

Read more on the underlying GEOS „Equals“ predicate, as described in PostGIS ST_Equals function.

Sintaksė

overlay_equals(layer, [expression], [filter], [limit], [cache=false])

[] žymi neprivalomus argumentus

Argumentai

  • layer - the layer whose overlay is checked

  • expression - an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.

  • filter - an optional expression to filter the target features to check. If not set, all the features will be checked.

  • limit - an optional integer to limit the number of matching features. If not set, all the matching features will be returned.

  • cache - set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)

Pavyzdžiai

  • overlay_equals('regions') → TRUE if the current feature is spatially equal to a region

  • overlay_equals('regions', filter:= population > 10000) → TRUE if the current feature is spatially equal to a region with a population greater than 10000

  • overlay_equals('regions', name) → an array of names, for the regions spatially equal to the current feature

  • array_to_string(overlay_equals('regions', name)) → a string as a comma separated list of names, for the regions spatially equal to the current feature

  • array_sort(overlay_equals(layer:='regions', expression:="name", filter:= population > 10000)) → an ordered array of names, for the regions spatially equal to the current feature and with a population greater than 10000

  • overlay_equals(layer:='regions', expression:= geom_to_wkt(@geometry), limit:=2) → an array of geometries (in WKT), for up to two regions spatially equal to the current feature

Further reading: array manipulation, Select by location algorithm

9.2.13.98. overlay_intersects

Returns whether the current feature spatially intersects at least one feature from a target layer, or an array of expression-based results for the features in the target layer intersected by the current feature.

Read more on the underlying GEOS „Intersects“ predicate, as described in PostGIS ST_Intersects function.

Sintaksė

overlay_intersects(layer, [expression], [filter], [limit], [cache=false], [min_overlap], [min_inscribed_circle_radius], [return_details], [sort_by_intersection_size])

[] žymi neprivalomus argumentus

Argumentai

  • layer - the layer whose overlay is checked

  • expression - an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.

  • filter - an optional expression to filter the target features to check. If not set, all the features will be checked.

  • limit - an optional integer to limit the number of matching features. If not set, all the matching features will be returned.

  • cache - set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)

  • min_overlap - defines an optional exclusion filter:

    • for polygons, a minimum area in current feature squared units for the intersection. If the intersection results in multiple polygons the intersection will be returned if at least one of the polygons has an area greater or equal to the value

    • for lines, a minimum length in current feature units. If the intersection results in multiple lines the intersection will be returned if at least one of the lines has a length greater or equal to the value.

  • min_inscribed_circle_radius - defines an optional exclusion filter (for polygons only): minimum radius in current feature units for the maximum inscribed circle of the intersection. If the intersection results in multiple polygons the intersection will be returned if at least one of the polygons has a radius for the maximum inscribed circle greater or equal to the value.

    Read more on the underlying GEOS predicate, as described in PostGIS ST_MaximumInscribedCircle function.

    This argument requires GEOS >= 3.9.

  • return_details - Set this to true to return a list of maps containing (key names in quotes) the feature ‚id‘, the expression ‚result‘ and the ‚overlap‘ value (of the largest element in case of multipart). The ‚radius‘ of the maximum inscribed circle is also returned when the target layer is a polygon. Only valid when used with the expression parameter

  • sort_by_intersection_size - only valid when used with an expression, set this to ‚des‘ to return the results ordered by the overlap value in descending order or set this to ‚asc‘ for ascending order.

Pavyzdžiai

  • overlay_intersects('regions') → TRUE if the current feature spatially intersects a region

  • overlay_intersects('regions', filter:= population > 10000) → TRUE if the current feature spatially intersects a region with a population greater than 10000

  • overlay_intersects('regions', name) → an array of names, for the regions intersected by the current feature

  • array_to_string(overlay_intersects('regions', name)) → a string as a comma separated list of names, for the regions intersected by the current feature

  • array_sort(overlay_intersects(layer:='regions', expression:="name", filter:= population > 10000)) → an ordered array of names, for the regions intersected by the current feature and with a population greater than 10000

  • overlay_intersects(layer:='regions', expression:= geom_to_wkt(@geometry), limit:=2) → an array of geometries (in WKT), for up to two regions intersected by the current feature

  • overlay_intersects(layer:='regions', min_overlap:=0.54) → TRUE if the current feature spatially intersects a region and the intersection area (of at least one of the parts in case of multipolygons) is greater or equal to 0.54

  • overlay_intersects(layer:='regions', min_inscribed_circle_radius:=0.54) → TRUE if the current feature spatially intersects a region and the intersection area maximum inscribed circle’s radius (of at least one of the parts in case of multipart) is greater or equal to 0.54

  • overlay_intersects(layer:='regions', expression:= geom_to_wkt(@geometry), return_details:=true) → an array of maps containing ‚id‘, ‚result‘, ‚overlap‘ and ‚radius‘

  • overlay_intersects(layer:='regions', expression:= geom_to_wkt(@geometry), sort_by_intersection_size:='des') → an array of geometries (in WKT) ordered by the overlap value in descending order

Further reading: intersects, array manipulation, Select by location algorithm

9.2.13.99. overlay_nearest

Returns whether the current feature has feature(s) from a target layer within a given distance, or an array of expression-based results for the features in the target layer within a distance from the current feature.

Note: This function can be slow and consume a lot of memory for large layers.

Sintaksė

overlay_nearest(layer, [expression], [filter], [limit=1], [max_distance], [cache=false])

[] žymi neprivalomus argumentus

Argumentai

  • layer - the target layer

  • expression - an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.

  • filter - an optional expression to filter the target features to check. If not set, all the features in the target layer will be used.

  • limit - an optional integer to limit the number of matching features. If not set, only the nearest feature will be returned. If set to -1, returns all the matching features.

  • max_distance - an optional distance to limit the search of matching features. If not set, all the features in the target layer will be used.

  • cache - set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)

Pavyzdžiai

  • overlay_nearest('airports') → TRUE if the „airports“ layer has at least one feature

  • overlay_nearest('airports', max_distance:= 5000) → TRUE if there is an airport within a distance of 5000 map units from the current feature

  • overlay_nearest('airports', name) → the name of the closest airport to the current feature, as an array

  • array_to_string(overlay_nearest('airports', name)) → the name of the closest airport to the current feature, as a string

  • overlay_nearest(layer:='airports', expression:= name, max_distance:= 5000) → the name of the closest airport within a distance of 5000 map units from the current feature, as an array

  • overlay_nearest(layer:='airports', expression:="name", filter:= "Use"='Civilian', limit:=3) → an array of names, for up to the three closest civilian airports ordered by distance

  • overlay_nearest(layer:='airports', expression:="name", limit:= -1, max_distance:= 5000) → an array of names, for all the airports within a distance of 5000 map units from the current feature, ordered by distance

Further reading: array manipulation, Join attributes by nearest algorithm

9.2.13.100. overlay_touches

Returns whether the current feature spatially touches at least one feature from a target layer, or an array of expression-based results for the features in the target layer touched by the current feature.

Read more on the underlying GEOS „Touches“ predicate, as described in PostGIS ST_Touches function.

Sintaksė

overlay_touches(layer, [expression], [filter], [limit], [cache=false])

[] žymi neprivalomus argumentus

Argumentai

  • layer - the layer whose overlay is checked

  • expression - an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.

  • filter - an optional expression to filter the target features to check. If not set, all the features will be checked.

  • limit - an optional integer to limit the number of matching features. If not set, all the matching features will be returned.

  • cache - set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)

Pavyzdžiai

  • overlay_touches('regions') → TRUE if the current feature spatially touches a region

  • overlay_touches('regions', filter:= population > 10000) → TRUE if the current feature spatially touches a region with a population greater than 10000

  • overlay_touches('regions', name) → an array of names, for the regions touched by the current feature

  • string_to_array(overlay_touches('regions', name)) → a string as a comma separated list of names, for the regions touched by the current feature

  • array_sort(overlay_touches(layer:='regions', expression:="name", filter:= population > 10000)) → an ordered array of names, for the regions touched by the current feature and with a population greater than 10000

  • overlay_touches(layer:='regions', expression:= geom_to_wkt(@geometry), limit:=2) → an array of geometries (in WKT), for up to two regions touched by the current feature

Further reading: touches, array manipulation, Select by location algorithm

9.2.13.101. overlay_within

Returns whether the current feature is spatially within at least one feature from a target layer, or an array of expression-based results for the features in the target layer that contain the current feature.

Read more on the underlying GEOS „Within“ predicate, as described in PostGIS ST_Within function.

Sintaksė

overlay_within(layer, [expression], [filter], [limit], [cache=false])

[] žymi neprivalomus argumentus

Argumentai

  • layer - the layer whose overlay is checked

  • expression - an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.

  • filter - an optional expression to filter the target features to check. If not set, all the features will be checked.

  • limit - an optional integer to limit the number of matching features. If not set, all the matching features will be returned.

  • cache - set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)

Pavyzdžiai

  • overlay_within('regions') → TRUE if the current feature is spatially within a region

  • overlay_within('regions', filter:= population > 10000) → TRUE if the current feature is spatially within a region with a population greater than 10000

  • overlay_within('regions', name) → an array of names, for the regions containing the current feature

  • array_to_string(overlay_within('regions', name)) → a string as a comma separated list of names, for the regions containing the current feature

  • array_sort(overlay_within(layer:='regions', expression:="name", filter:= population > 10000)) → an ordered array of names, for the regions containing the current feature and with a population greater than 10000

  • overlay_within(layer:='regions', expression:= geom_to_wkt(@geometry), limit:=2) → an array of geometries (in WKT), for up to two regions containing the current feature

Further reading: within, array manipulation, Select by location algorithm

9.2.13.102. $perimeter

Returns the perimeter length of the current feature. The perimeter calculated by this function respects both the current project’s ellipsoid setting and distance unit settings. For example, if an ellipsoid has been set for the project then the calculated perimeter will be ellipsoidal, and if no ellipsoid is set then the calculated perimeter will be planimetric.

Sintaksė

$perimeter

Pavyzdžiai

  • $perimeter → 42

9.2.13.103. perimeter

Returns the perimeter of a geometry polygon object. Calculations are always planimetric in the Spatial Reference System (SRS) of this geometry, and the units of the returned perimeter will match the units for the SRS. This differs from the calculations performed by the $perimeter function, which will perform ellipsoidal calculations based on the project’s ellipsoid and distance unit settings.

Sintaksė

perimeter(geometry)

Argumentai

  • geometry - polygon geometry object

Pavyzdžiai

  • perimeter(geom_from_wkt('POLYGON((0 0, 4 0, 4 2, 0 2, 0 0))')) → 12.0

9.2.13.104. point_n

Returns a specific node from a geometry.

Sintaksė

point_n(geometry, index)

Argumentai

  • geometry - geometry object

  • index - index of node to return, where 1 is the first node; if the value is negative, the selected vertex index will be its total count minus the absolute value

Pavyzdžiai

  • geom_to_wkt(point_n(geom_from_wkt('POLYGON((0 0, 4 0, 4 2, 0 2, 0 0))'),2)) → ‚Point (4 0)‘

Further reading: Extract specific vertices algorithm

9.2.13.105. point_on_surface

Returns a point guaranteed to lie on the surface of a geometry.

Sintaksė

point_on_surface(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • point_on_surface(@geometry) → a point geometry

Further reading: Point on Surface algorithm

9.2.13.106. pole_of_inaccessibility

Calculates the approximate pole of inaccessibility for a surface, which is the most distant internal point from the boundary of the surface. This function uses the ‚polylabel‘ algorithm (Vladimir Agafonkin, 2016), which is an iterative approach guaranteed to find the true pole of inaccessibility within a specified tolerance. More precise tolerances require more iterations and will take longer to calculate.

Sintaksė

pole_of_inaccessibility(geometry, tolerance)

Argumentai

  • geometry - a geometry

  • tolerance - maximum distance between the returned point and the true pole location

Pavyzdžiai

  • geom_to_wkt(pole_of_inaccessibility( geom_from_wkt('POLYGON((0 1, 0 9, 3 10, 3 3, 10 3, 10 1, 0 1))'), 0.1)) → ‚Point(1.546875 2.546875)‘

../../../_images/pole_inaccessibility.png

Fig. 9.24 Pole of inaccessibility

Further reading: Pole of inaccessibility algorithm

9.2.13.107. project

Returns a point projected from a start point using a distance, a bearing (azimuth) and an elevation in radians.

Sintaksė

project(point, distance, azimuth, [elevation])

[] žymi neprivalomus argumentus

Argumentai

  • point - start point

  • distance - distance to project

  • azimuth - azimuth in radians clockwise, where 0 corresponds to north

  • elevation - angle of inclination in radians

Pavyzdžiai

  • geom_to_wkt(project(make_point(1, 2), 3, radians(270))) → ‚Point(-2, 2)‘

Further reading: Project points (Cartesian) algorithm

9.2.13.108. relate

Tests the Dimensional Extended 9 Intersection Model (DE-9IM) representation of the relationship between two geometries.

Relationship variant

Returns the Dimensional Extended 9 Intersection Model (DE-9IM) representation of the relationship between two geometries.

Sintaksė

relate(geometry, geometry)

Argumentai

  • geometry - a geometry

  • geometry - a geometry

Pavyzdžiai

  • relate( geom_from_wkt( 'LINESTRING(40 40,120 120)' ), geom_from_wkt( 'LINESTRING(40 40,60 120)' ) ) → ‚FF1F00102‘

Pattern match variant

Tests whether the DE-9IM relationship between two geometries matches a specified pattern.

Sintaksė

relate(geometry, geometry, pattern)

Argumentai

  • geometry - a geometry

  • geometry - a geometry

  • pattern - DE-9IM pattern to match

Pavyzdžiai

  • relate( geom_from_wkt( 'LINESTRING(40 40,120 120)' ), geom_from_wkt( 'LINESTRING(40 40,60 120)' ), '**1F001**' ) → TRUE

9.2.13.109. reverse

Reverses the direction of a line string by reversing the order of its vertices.

Sintaksė

reverse(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • geom_to_wkt(reverse(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2)'))) → ‚LINESTRING(2 2, 1 1, 0 0)‘

../../../_images/reverse_line.png

Fig. 9.25 Reversing line direction

Further reading: Reverse line direction algorithm

9.2.13.110. rotate

Returns a rotated version of a geometry. Calculations are in the Spatial Reference System of this geometry.

Sintaksė

rotate(geometry, rotation, [center=NULL], [per_part=false])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • rotation - clockwise rotation in degrees

  • center - rotation center point. If not specified, the center of the geometry’s bounding box is used.

  • per_part - apply rotation per part. If true, then rotation will apply around the center of each part’s bounding box when the input geometry is multipart and an explicit rotation center point is not specified.

Pavyzdžiai

  • rotate(@geometry, 45, make_point(4, 5)) → geometry rotated 45 degrees clockwise around the (4, 5) point

  • rotate(@geometry, 45) → geometry rotated 45 degrees clockwise around the center of its bounding box

../../../_images/rotate.gif

Fig. 9.26 Rotating features

9.2.13.111. roundness

Calculates how close a polygon shape is to a circle. The function Returns TRUE when the polygon shape is a perfect circle and 0 when it is completely flat.

Sintaksė

roundness(geometry)

Argumentai

  • geometry - a polygon

Pavyzdžiai

  • round(roundness(geom_from_wkt('POLYGON(( 0 0, 0 1, 1 1, 1 0, 0 0))')), 3) → 0.785

  • round(roundness(geom_from_wkt('POLYGON(( 0 0, 0 0.1, 1 0.1, 1 0, 0 0))')), 3) → 0.260

Further reading: Roundness algorithm

9.2.13.112. scale

Returns a scaled version of a geometry. Calculations are in the Spatial Reference System of this geometry.

Sintaksė

scale(geometry, x_scale, y_scale, [center])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • x_scale - x-axis scaling factor

  • y_scale - y-axis scaling factor

  • center - scaling center point. If not specified, the center of the geometry’s bounding box is used.

Pavyzdžiai

  • scale(@geometry, 2, 0.5, make_point(4, 5)) → geometry scaled twice horizontally and halved vertically, around the (4, 5) point

  • scale(@geometry, 2, 0.5) → geometry twice horizontally and halved vertically, around the center of its bounding box

9.2.13.113. segments_to_lines

Returns a multi line geometry consisting of a line for every segment in the input geometry.

Sintaksė

segments_to_lines(geometry)

Argumentai

  • geometry - geometry object

Pavyzdžiai

  • geom_to_wkt(segments_to_lines(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2)'))) → ‚MultiLineString ((0 0, 1 1),(1 1, 2 2))‘

Further reading: Explode lines algorithm

9.2.13.114. shared_paths

Returns a collection containing paths shared by the two input geometries. Those going in the same direction are in the first element of the collection, those going in the opposite direction are in the second element. The paths themselves are given in the direction of the first geometry.

Sintaksė

shared_paths(geometry1, geometry2)

Argumentai

  • geometry1 - a LineString/MultiLineString geometry

  • geometry2 - a LineString/MultiLineString geometry

Pavyzdžiai

  • geom_to_wkt(shared_paths(geom_from_wkt('MULTILINESTRING((26 125,26 200,126 200,126 125,26 125),(51 150,101 150,76 175,51 150)))'),geom_from_wkt('LINESTRING(151 100,126 156.25,126 125,90 161, 76 175)'))) → ‚GeometryCollection (MultiLineString ((126 156.25, 126 125),(101 150, 90 161),(90 161, 76 175)),MultiLineString EMPTY)‘

  • geom_to_wkt(shared_paths(geom_from_wkt('LINESTRING(76 175,90 161,126 125,126 156.25,151 100)'),geom_from_wkt('MULTILINESTRING((26 125,26 200,126 200,126 125,26 125),(51 150,101 150,76 175,51 150))'))) → ‚GeometryCollection (MultiLineString EMPTY,MultiLineString ((76 175, 90 161),(90 161, 101 150),(126 125, 126 156.25)))‘

9.2.13.115. shortest_line

Returns the shortest line joining geometry1 to geometry2. The resultant line will start at geometry1 and end at geometry2.

Sintaksė

shortest_line(geometry1, geometry2)

Argumentai

  • geometry1 - geometry to find shortest line from

  • geometry2 - geometry to find shortest line to

Pavyzdžiai

  • geom_to_wkt(shortest_line(geom_from_wkt('LINESTRING (20 80, 98 190, 110 180, 50 75 )'),geom_from_wkt('POINT(100 100)'))) → ‚LineString(73.0769 115.384, 100 100)‘

9.2.13.116. simplify

Simplifies a geometry by removing nodes using a distance based threshold (ie, the Douglas Peucker algorithm). The algorithm preserves large deviations in geometries and reduces the number of vertices in nearly straight segments.

Sintaksė

simplify(geometry, tolerance)

Argumentai

  • geometry - a geometry

  • tolerance - maximum deviation from straight segments for points to be removed

Pavyzdžiai

  • geom_to_wkt(simplify(geometry:=geom_from_wkt('LineString(0 0, 5 0.1, 10 0)'),tolerance:=5)) → ‚LineString(0 0, 10 0)‘

../../../_images/simplify_geometries.png

Fig. 9.27 From left to right, source layer and increasing simplification tolerances

Further reading: Simplify algorithm

9.2.13.117. simplify_vw

Simplifies a geometry by removing nodes using an area based threshold (ie, the Visvalingam-Whyatt algorithm). The algorithm removes vertices which create small areas in geometries, e.g., narrow spikes or nearly straight segments.

Sintaksė

simplify_vw(geometry, tolerance)

Argumentai

  • geometry - a geometry

  • tolerance - a measure of the maximum area created by a node for the node to be removed

Pavyzdžiai

  • geom_to_wkt(simplify_vw(geometry:=geom_from_wkt('LineString(0 0, 5 0, 5.01 10, 5.02 0, 10 0)'),tolerance:=5)) → ‚LineString(0 0, 10 0)‘

Further reading: Simplify algorithm

9.2.13.118. single_sided_buffer

Returns a geometry formed by buffering out just one side of a linestring geometry. Distances are in the Spatial Reference System of this geometry.

Sintaksė

single_sided_buffer(geometry, distance, [segments=8], [join=1], [miter_limit=2.0])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a (multi)linestring geometry

  • distance - buffer distance. Positive values will be buffered to the left of lines, negative values to the right

  • segments - number of segments to use to represent a quarter circle when a round join style is used. A larger number results in a smoother buffer with more nodes.

  • join - join style for corners, where 1 = round, 2 = miter and 3 = bevel

  • miter_limit - limit on the miter ratio used for very sharp corners (when using miter joins only)

Pavyzdžiai

  • single_sided_buffer(@geometry, 10.5) → line buffered to the left by 10.5 units

  • single_sided_buffer(@geometry, -10.5) → line buffered to the right by 10.5 units

  • single_sided_buffer(@geometry, 10.5, segments:=16, join:=1) → line buffered to the left by 10.5 units, using more segments to result in a smoother buffer

  • single_sided_buffer(@geometry, 10.5, join:=3) → line buffered to the left by 10.5 units, using a beveled join

../../../_images/single_side_buffer.png

Fig. 9.28 Left versus right side buffer on the same vector line layer

Further reading: Single sided buffer algorithm

9.2.13.119. sinuosity

Returns the sinuosity of a curve, which is the ratio of the curve length to the straight (2D) distance between its endpoints.

Sintaksė

sinuosity(geometry)

Argumentai

  • geometry - Input curve (circularstring, linestring)

Pavyzdžiai

  • round(sinuosity(geom_from_wkt('LINESTRING(2 0, 2 2, 3 2, 3 3)')), 3) → 1.265

  • sinuosity(geom_from_wkt('LINESTRING( 3 1, 5 1)')) → 1.0

9.2.13.120. smooth

Smooths a geometry by adding extra nodes which round off corners in the geometry. If input geometries contain Z or M values, these will also be smoothed and the output geometry will retain the same dimensionality as the input geometry.

Sintaksė

smooth(geometry, [iterations=1], [offset=0.25], [min_length=-1], [max_angle=180])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • iterations - number of smoothing iterations to apply. Larger numbers result in smoother but more complex geometries.

  • offset - value between 0 and 0.5 which controls how tightly the smoothed geometry follow the original geometry. Smaller values result in a tighter smoothing, larger values result in looser smoothing.

  • min_length - minimum length of segments to apply smoothing to. This parameter can be used to avoid placing excessive additional nodes in shorter segments of the geometry.

  • max_angle - maximum angle at node for smoothing to be applied (0-180). By lowering the maximum angle intentionally sharp corners in the geometry can be preserved. For instance, a value of 80 degrees will retain right angles in the geometry.

Pavyzdžiai

  • geom_to_wkt(smooth(geometry:=geom_from_wkt('LineString(0 0, 5 0, 5 5)'),iterations:=1,offset:=0.2,min_length:=-1,max_angle:=180)) → ‚LineString (0 0, 4 0, 5 1, 5 5)‘

../../../_images/smooth_geometry_1.png

Fig. 9.29 Increasing number of iterations causes smoother geometries

Further reading: Smooth algorithm

9.2.13.121. square_wave

Constructs square/rectangular waves along the boundary of a geometry.

Sintaksė

square_wave(geometry, wavelength, amplitude, [strict=False])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • wavelength - wavelength of square waveform

  • amplitude - amplitude of square waveform

  • strict - By default the wavelength argument is treated as a „maximum wavelength“, where the actual wavelength will be dynamically adjusted so that an exact number of square waves are created along the boundaries of the geometry. If the strict argument is set to true then the wavelength will be used exactly and an incomplete pattern may be used for the final waveform.

Pavyzdžiai

  • square_wave(geom_from_wkt('LineString(0 0, 10 0)'), 3, 1) → Square waves with wavelength 3 and amplitude 1 along the linestring

../../../_images/square_wave.png

Fig. 9.30 Symbolizing features with square waves

9.2.13.122. square_wave_randomized

Constructs randomized square/rectangular waves along the boundary of a geometry.

Sintaksė

square_wave_randomized(geometry, min_wavelength, max_wavelength, min_amplitude, max_amplitude, [seed=0])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • min_wavelength - minimum wavelength of waves

  • max_wavelength - maximum wavelength of waves

  • min_amplitude - minimum amplitude of waves

  • max_amplitude - maximum amplitude of waves

  • seed - specifies a random seed for generating waves. If the seed is 0, then a completely random set of waves will be generated.

Pavyzdžiai

  • square_wave_randomized(geom_from_wkt('LineString(0 0, 10 0)'), 2, 3, 0.1, 0.2) → Randomly sized square waves with wavelengths between 2 and 3 and amplitudes between 0.1 and 0.2 along the linestring

../../../_images/square_wave_randomized.png

Fig. 9.31 Symbolizing features with square randomized waves

9.2.13.123. start_point

Returns the first node from a geometry.

Sintaksė

start_point(geometry)

Argumentai

  • geometry - geometry object

Pavyzdžiai

  • geom_to_wkt(start_point(geom_from_wkt('LINESTRING(4 0, 4 2, 0 2)'))) → ‚Point (4 0)‘

../../../_images/start_point.png

Fig. 9.32 Starting point of a line feature

Further reading: end_point, Extract specific vertices algorithm

9.2.13.124. straight_distance_2d

Returns the direct/euclidean distance between the first and last vertex of a geometry. The geometry must be a curve (circularstring, linestring).

Sintaksė

straight_distance_2d(geometry)

Argumentai

  • geometry - The geometry.

Pavyzdžiai

  • straight_distance_2d(geom_from_wkt('LINESTRING(1 0, 1 1)')) → 1

  • round(straight_distance_2d(geom_from_wkt('LINESTRING(1 4, 3 5, 5 0)')), 3) → 5.657

Further reading: length

9.2.13.125. sym_difference

Returns a geometry that represents the portions of two geometries that do not intersect.

Sintaksė

sym_difference(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • geom_to_wkt( sym_difference( geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ), geom_from_wkt( 'LINESTRING(3 3, 8 8)' ) ) ) → ‚LINESTRING(5 5, 8 8)‘

Further reading: Symmetrical difference algorithm

9.2.13.126. tapered_buffer

Creates a buffer along a line geometry where the buffer diameter varies evenly over the length of the line.

Sintaksė

tapered_buffer(geometry, start_width, end_width, [segments=8])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - input geometry. Must be a (multi)line geometry.

  • start_width - width of buffer at start of line,

  • end_width - width of buffer at end of line.

  • segments - number of segments to approximate quarter-circle curves in the buffer.

Pavyzdžiai

  • tapered_buffer(geometry:=geom_from_wkt('LINESTRING(1 2, 4 2)'),start_width:=1,end_width:=2,segments:=8) → A tapered buffer starting with a diameter of 1 and ending with a diameter of 2 along the linestring geometry.

../../../_images/tapered_buffer.png

Fig. 9.33 Tapered buffer on line features

Further reading: Tapered buffers algorithm

9.2.13.127. touches

Tests whether a geometry touches another. Returns TRUE if the geometries have at least one point in common, but their interiors do not intersect.

Sintaksė

touches(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • touches( geom_from_wkt( 'LINESTRING(5 3, 4 4)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → TRUE

  • touches( geom_from_wkt( 'POINT(4 4)' ), geom_from_wkt( 'POINT(5 5)' ) ) → FALSE

Further reading: overlay_touches

9.2.13.128. transform

Returns the geometry transformed from a source CRS to a destination CRS.

Sintaksė

transform(geometry, source_auth_id, dest_auth_id)

Argumentai

  • geometry - a geometry

  • source_auth_id - the source auth CRS ID

  • dest_auth_id - the destination auth CRS ID

Pavyzdžiai

  • geom_to_wkt( transform( make_point(488995.53240249, 7104473.38600835), 'EPSG:2154', 'EPSG:4326' ) ) → ‚POINT(0 51)‘

Further reading: Reproject layer algorithm

9.2.13.129. translate

Returns a translated version of a geometry. Calculations are in the Spatial Reference System of this geometry.

Sintaksė

translate(geometry, dx, dy)

Argumentai

  • geometry - a geometry

  • dx - delta x

  • dy - delta y

Pavyzdžiai

  • translate(@geometry, 5, 10) → a geometry of the same type like the original one

../../../_images/translate_geometry.png

Fig. 9.34 Translating features

Further reading: Translate algorithm

9.2.13.130. triangular_wave

Constructs triangular waves along the boundary of a geometry.

Sintaksė

triangular_wave(geometry, wavelength, amplitude, [strict=False])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • wavelength - wavelength of triangular waveform

  • amplitude - amplitude of triangular waveform

  • strict - By default the wavelength argument is treated as a „maximum wavelength“, where the actual wavelength will be dynamically adjusted so that an exact number of triangular waves are created along the boundaries of the geometry. If the strict argument is set to true then the wavelength will be used exactly and an incomplete pattern may be used for the final waveform.

Pavyzdžiai

  • triangular_wave(geom_from_wkt('LineString(0 0, 10 0)'), 3, 1) → Triangular waves with wavelength 3 and amplitude 1 along the linestring

../../../_images/triangular_wave.png

Fig. 9.35 Symbolizing features with triangular waves

9.2.13.131. triangular_wave_randomized

Constructs randomized triangular waves along the boundary of a geometry.

Sintaksė

triangular_wave_randomized(geometry, min_wavelength, max_wavelength, min_amplitude, max_amplitude, [seed=0])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • min_wavelength - minimum wavelength of waves

  • max_wavelength - maximum wavelength of waves

  • min_amplitude - minimum amplitude of waves

  • max_amplitude - maximum amplitude of waves

  • seed - specifies a random seed for generating waves. If the seed is 0, then a completely random set of waves will be generated.

Pavyzdžiai

  • triangular_wave_randomized(geom_from_wkt('LineString(0 0, 10 0)'), 2, 3, 0.1, 0.2) → Randomly sized triangular waves with wavelengths between 2 and 3 and amplitudes between 0.1 and 0.2 along the linestring

../../../_images/triangular_wave_randomized.png

Fig. 9.36 Symbolizing features with triangular randomized waves

9.2.13.132. union

Returns a geometry that represents the point set union of the geometries.

Sintaksė

union(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • geom_to_wkt( union( make_point(4, 4), make_point(5, 5) ) ) → ‚MULTIPOINT(4 4, 5 5)‘

9.2.13.133. wave

Constructs rounded (sine-like) waves along the boundary of a geometry.

Sintaksė

wave(geometry, wavelength, amplitude, [strict=False])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • wavelength - wavelength of sine-like waveform

  • amplitude - amplitude of sine-like waveform

  • strict - By default the wavelength argument is treated as a „maximum wavelength“, where the actual wavelength will be dynamically adjusted so that an exact number of waves are created along the boundaries of the geometry. If the strict argument is set to true then the wavelength will be used exactly and an incomplete pattern may be used for the final waveform.

Pavyzdžiai

  • wave(geom_from_wkt('LineString(0 0, 10 0)'), 3, 1) → Sine-like waves with wavelength 3 and amplitude 1 along the linestring

../../../_images/wave.png

Fig. 9.37 Symbolizing features with waves

9.2.13.134. wave_randomized

Constructs randomized curved (sine-like) waves along the boundary of a geometry.

Sintaksė

wave_randomized(geometry, min_wavelength, max_wavelength, min_amplitude, max_amplitude, [seed=0])

[] žymi neprivalomus argumentus

Argumentai

  • geometry - a geometry

  • min_wavelength - minimum wavelength of waves

  • max_wavelength - maximum wavelength of waves

  • min_amplitude - minimum amplitude of waves

  • max_amplitude - maximum amplitude of waves

  • seed - specifies a random seed for generating waves. If the seed is 0, then a completely random set of waves will be generated.

Pavyzdžiai

  • wave_randomized(geom_from_wkt('LineString(0 0, 10 0)'), 2, 3, 0.1, 0.2) → Randomly sized curved waves with wavelengths between 2 and 3 and amplitudes between 0.1 and 0.2 along the linestring

../../../_images/wave_randomized.png

Fig. 9.38 Symbolizing features with randomized waves

9.2.13.135. wedge_buffer

Returns a wedge shaped buffer originating from a point geometry.

Sintaksė

wedge_buffer(center, azimuth, width, outer_radius, [inner_radius=0.0])

[] žymi neprivalomus argumentus

Argumentai

  • center - center point (origin) of buffer. Must be a point geometry.

  • azimuth - angle (in degrees) for the middle of the wedge to point.

  • width - buffer width (in degrees). Note that the wedge will extend to half of the angular width either side of the azimuth direction.

  • outer_radius - outer radius for buffers

  • inner_radius - optional inner radius for buffers

Pavyzdžiai

  • wedge_buffer(center:=geom_from_wkt('POINT(1 2)'),azimuth:=90,width:=180,outer_radius:=1) → A wedge shaped buffer centered on the point (1,2), facing to the East, with a width of 180 degrees and outer radius of 1.

../../../_images/wedge_buffers.png

Fig. 9.39 Wedge buffering features

Further reading: Create wedge buffers algorithm

9.2.13.136. within

Tests whether a geometry is within another. Returns TRUE if the geometry1 is completely within geometry2.

Sintaksė

within(geometry1, geometry2)

Argumentai

  • geometry1 - a geometry

  • geometry2 - a geometry

Pavyzdžiai

  • within( geom_from_wkt( 'POINT( 0.5 0.5)' ), geom_from_wkt( 'POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))' ) ) → TRUE

  • within( geom_from_wkt( 'POINT( 5 5 )' ), geom_from_wkt( 'POLYGON((0 0, 0 1, 1 1, 1 0, 0 0 ))' ) ) → FALSE

Further reading: overlay_within

9.2.13.137. $x

Returns the x coordinate of the current point feature. If the feature is a multipoint feature, then the x-coordinate of the first point will be returned. WARNING: This function is deprecated. It is recommended to use the replacement x() function with @geometry variable instead.

Sintaksė

$x

Pavyzdžiai

  • $x → 42

Further reading: x

9.2.13.138. x

Returns the x coordinate of a point geometry, or the x coordinate of the centroid for a non-point geometry.

Sintaksė

x(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • x( geom_from_wkt( 'POINT(2 5)' ) ) → 2

  • x( @geometry ) → x coordinate of the current feature’s centroid

9.2.13.139. $x_at

Retrieves a x coordinate of the current feature’s geometry. WARNING: This function is deprecated. It is recommended to use the replacement x_at function with @geometry variable instead.

Sintaksė

$x_at(vertex)

Argumentai

  • vertex - index of the vertex of the current geometry (indices start at 0; negative values apply from the last index, starting at -1)

Pavyzdžiai

  • $x_at(1) → 5

Further reading: x_at

9.2.13.140. x_at

Retrieves a x coordinate of the geometry.

Sintaksė

x_at(geometry, vertex)

Argumentai

  • geometry - geometry object

  • vertex - index of the vertex of the geometry (indices start at 0; negative values apply from the last index, starting at -1)

Pavyzdžiai

  • x_at( geom_from_wkt( 'POINT(4 5)' ), 0 ) → 4

9.2.13.141. x_max

Returns the maximum x coordinate of a geometry. Calculations are in the spatial reference system of this geometry.

Sintaksė

x_max(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • x_max( geom_from_wkt( 'LINESTRING(2 5, 3 6, 4 8)') ) → 4

9.2.13.142. x_min

Returns the minimum x coordinate of a geometry. Calculations are in the spatial reference system of this geometry.

Sintaksė

x_min(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • x_min( geom_from_wkt( 'LINESTRING(2 5, 3 6, 4 8)') ) → 2

9.2.13.143. $y

Returns the y coordinate of the current point feature. If the feature is a multipoint feature, then the y-coordinate of the first point will be returned. WARNING: This function is deprecated. It is recommended to use the replacement y() function with @geometry variable instead.

Sintaksė

$y

Pavyzdžiai

  • $y → 42

Further reading: y

9.2.13.144. y

Returns the y coordinate of a point geometry, or the y coordinate of the centroid for a non-point geometry.

Sintaksė

y(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • y( geom_from_wkt( 'POINT(2 5)' ) ) → 5

  • y( @geometry ) → y coordinate of the current feature’s centroid

9.2.13.145. $y_at

Retrieves a y coordinate of the current feature’s geometry. WARNING: This function is deprecated. It is recommended to use the replacement y_at function with @geometry variable instead.

Sintaksė

$y_at(vertex)

Argumentai

  • vertex - index of the vertex of the current geometry (indices start at 0; negative values apply from the last index, starting at -1)

Pavyzdžiai

  • $y_at(1) → 2

Further reading: y_at

9.2.13.146. y_at

Retrieves a y coordinate of the geometry.

Sintaksė

y_at(geometry, vertex)

Argumentai

  • geometry - geometry object

  • vertex - index of the vertex of the geometry (indices start at 0; negative values apply from the last index, starting at -1)

Pavyzdžiai

  • y_at( geom_from_wkt( 'POINT(4 5)' ), 0 ) → 5

9.2.13.147. y_max

Returns the maximum y coordinate of a geometry. Calculations are in the spatial reference system of this geometry.

Sintaksė

y_max(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • y_max( geom_from_wkt( 'LINESTRING(2 5, 3 6, 4 8)') ) → 8

9.2.13.148. y_min

Returns the minimum y coordinate of a geometry. Calculations are in the spatial reference system of this geometry.

Sintaksė

y_min(geometry)

Argumentai

  • geometry - a geometry

Pavyzdžiai

  • y_min( geom_from_wkt( 'LINESTRING(2 5, 3 6, 4 8)') ) → 5

9.2.13.149. $z

Returns the z value of the current point feature if it is 3D. If the feature is a multipoint feature, then the z value of the first point will be returned. WARNING: This function is deprecated. It is recommended to use the replacement z() function with @geometry variable instead.

Sintaksė

$z

Pavyzdžiai

  • $z → 123

9.2.13.150. z

Returns the z coordinate of a point geometry, or NULL if the geometry has no z value.

Sintaksė

z(geometry)

Argumentai

  • geometry - a point geometry

Pavyzdžiai

  • z( geom_from_wkt( 'POINTZ(2 5 7)' ) ) → 7

9.2.13.151. z_at

Retrieves a z coordinate of the geometry, or NULL if the geometry has no z value.

Sintaksė

z_at(geometry, vertex)

Argumentai

  • geometry - geometry object

  • vertex - index of the vertex of the geometry (indices start at 0; negative values apply from the last index, starting at -1)

Pavyzdžiai

  • z_at(geom_from_wkt('LineStringZ(0 0 0, 10 10 5, 10 10 0)'), 1) → 5

9.2.13.152. z_max

Returns the maximum z coordinate of a geometry, or NULL if the geometry has no z value.

Sintaksė

z_max(geometry)

Argumentai

  • geometry - a geometry with z coordinate

Pavyzdžiai

  • z_max( geom_from_wkt( 'POINT ( 0 0 1 )' ) ) → 1

  • z_max( geom_from_wkt( 'MULTIPOINT ( 0 0 1 , 1 1 3 )' ) ) → 3

  • z_max( make_line( make_point( 0,0,0 ), make_point( -1,-1,-2 ) ) ) → 0

  • z_max( geom_from_wkt( 'LINESTRING( 0 0 0, 1 0 2, 1 1 -1 )' ) ) → 2

  • z_max( geom_from_wkt( 'POINT ( 0 0 )' ) ) → NULL

9.2.13.153. z_min

Returns the minimum z coordinate of a geometry, or NULL if the geometry has no z value.

Sintaksė

z_min(geometry)

Argumentai

  • geometry - a geometry with z coordinate

Pavyzdžiai

  • z_min( geom_from_wkt( 'POINT ( 0 0 1 )' ) ) → 1

  • z_min( geom_from_wkt( 'MULTIPOINT ( 0 0 1 , 1 1 3 )' ) ) → 1

  • z_min( make_line( make_point( 0,0,0 ), make_point( -1,-1,-2 ) ) ) → -2

  • z_min( geom_from_wkt( 'LINESTRING( 0 0 0, 1 0 2, 1 1 -1 )' ) ) → -1

  • z_min( geom_from_wkt( 'POINT ( 0 0 )' ) ) → NULL

9.2.14. Layout Functions

This group contains functions to manipulate print layout items properties.

9.2.14.1. item_variables

Returns a map of variables from a layout item inside this print layout.

Sintaksė

item_variables(id)

Argumentai

  • id - layout item ID

Pavyzdžiai

  • map_get( item_variables('Map 0'), 'map_scale') → scale of the item ‚Map 0‘ in the current print layout

Further reading: List of default variables

9.2.14.2. map_credits

Returns a list of credit (usage rights) strings for the layers shown in a layout, or specific layout map item.

Sintaksė

map_credits([id], [include_layer_names=false], [layer_name_separator=‘: ‚])

[] žymi neprivalomus argumentus

Argumentai

  • id - Map item ID. If not specified, the layers from all maps in the layout will be used.

  • include_layer_names - Set to true to include layer names before their credit strings

  • layer_name_separator - String to insert between layer names and their credit strings, if include_layer_names is true

Pavyzdžiai

  • array_to_string( map_credits() ) → comma separated list of layer credits for all layers shown in all map items in the layout, e.g ‚CC-BY-NC, CC-BY-SA‘

  • array_to_string( map_credits( 'Main Map' ) ) → comma separated list of layer credits for layers shown in the ‚Main Map‘ layout item, e.g ‚CC-BY-NC, CC-BY-SA‘

  • array_to_string( map_credits( 'Main Map', include_layer_names := true, layer_name_separator := ': ' ) ) → comma separated list of layer names and their credits for layers shown in the ‚Main Map‘ layout item, e.g. ‚Railway lines: CC-BY-NC, Basemap: CC-BY-SA‘

This function requires the Access metadata properties of the layers to have been filled.

9.2.15. Map Layers

This group contains a list of the available layers in the current project and, for each layer, their fields (stored in the dataset, virtual or auxiliary ones as well as from joins). The fields can be interacted the same way as mentioned in Fields and Values, except that a double-click will add the name as a string (single quoted) to the expression instead of as a field reference given that they do not belong to the active layer. This offers a convenient way to write expressions referring to different layers, such as when performing aggregates, attribute or spatial queries.

It also provides some convenient functions to manipulate layers.

9.2.15.1. decode_uri

Takes a layer and decodes the uri of the underlying data provider. It depends on the dataprovider, which data is available.

Sintaksė

decode_uri(layer, [part])

[] žymi neprivalomus argumentus

Argumentai

  • layer - The layer for which the uri should be decoded.

  • part - The part of the uri to return. If unspecified, a map with all uri parts will be returned.

Pavyzdžiai

  • decode_uri(@layer) → {‚layerId‘: ‚0‘, ‚layerName‘: ‚‘, ‚path‘: ‚/home/qgis/shapefile.shp‘}

  • decode_uri(@layer) → {‚layerId‘: NULL, ‚layerName‘: ‚layer‘, ‚path‘: ‚/home/qgis/geopackage.gpkg‘}

  • decode_uri(@layer, 'path') → ‚C:\my_data\qgis\shape.shp‘

9.2.15.2. layer_property

Returns a matching layer property or metadata value.

Sintaksė

layer_property(layer, property)

Argumentai

  • layer - tekstas, reprezentuojantis arba sluoksnio pavadinimą, arba sluoksnio ID

  • property - a string corresponding to the property to return. Valid options are:

    • name: layer name

    • id: layer ID

    • title: metadata title string

    • abstract: metadata abstract string

    • keywords: metadata keywords

    • data_url: metadata URL

    • attribution: metadata attribution string

    • attribution_url: metadata attribution URL

    • source: layer source

    • min_scale: minimum display scale for layer

    • max_scale: maximum display scale for layer

    • is_editable: if layer is in edit mode

    • crs: layer CRS

    • crs_definition: layer CRS full definition

    • crs_description: layer CRS description

    • crs_ellipsoid: acronym of the layer CRS ellipsoid

    • extent: layer extent (as a geometry object)

    • distance_units: layer distance units

    • type: layer type, e.g., Vector or Raster

    • storage_type: storage format (vector layers only)

    • geometry_type: geometry type, e.g., Point (vector layers only)

    • feature_count: approximate feature count for layer (vector layers only)

    • path: File path to the layer data source. Only available for file based layers.

Pavyzdžiai

  • layer_property('streets','title') → ‚Basemap Streets‘

  • layer_property('airports','feature_count') → 120

  • layer_property('landsat','crs') → ‚EPSG:4326‘

Further reading: vector, raster and mesh layer properties

9.2.15.3. load_layer

Loads a layer by source URI and provider name.

Sintaksė

load_layer(uri, provider)

Argumentai

  • uri - layer source URI string

  • provider - layer data provider name

Pavyzdžiai

  • layer_property(load_layer('c:/data/roads.shp', 'ogr'), 'feature_count') → count of features from the c:/data/roads.shp vector layer

9.2.16. Maps Functions

This group contains functions to create or manipulate keys and values of map data structures (also known as dictionary objects, key-value pairs, or associative arrays). Unlike the list data structure where values order matters, the order of the key-value pairs in the map object is not relevant and values are identified by their keys.

9.2.16.1. from_json

Loads a JSON formatted string.

Sintaksė

from_json(string)

Argumentai

  • string - JSON string

Pavyzdžiai

  • from_json('{"1":"one","2":"two"}') → { ‚1‘: ‚one‘, ‚2‘: ‚two‘ }

  • from_json('[1,2,3]') → [1,2,3]

9.2.16.2. hstore_to_map

Creates a map from a hstore-formatted string.

Sintaksė

hstore_to_map(string)

Argumentai

  • string - the input string

Pavyzdžiai

  • hstore_to_map('qgis=>rocks') → { ‚qgis‘: ‚rocks‘ }

9.2.16.3. map

Returns a map containing all the keys and values passed as pair of parameters.

Sintaksė

map(key1, value1, key2, value2, …)

Argumentai

  • key - a key (string)

  • value - a value

Pavyzdžiai

  • map('1','one','2', 'two') → { ‚1‘: ‚one‘, ‚2‘: ‚two‘ }

  • map('1','one','2', 'two')['1'] → ‚one‘

9.2.16.4. map_akeys

Returns all the keys of a map as an array.

Sintaksė

map_akeys(map)

Argumentai

  • map - a map

Pavyzdžiai

  • map_akeys(map('1','one','2','two')) → [ ‚1‘, ‚2‘ ]

9.2.16.5. map_avals

Returns all the values of a map as an array.

Sintaksė

map_avals(map)

Argumentai

  • map - a map

Pavyzdžiai

  • map_avals(map('1','one','2','two')) → [ ‚one‘, ‚two‘ ]

9.2.16.6. map_concat

Returns a map containing all the entries of the given maps. If two maps contain the same key, the value of the second map is taken.

Sintaksė

map_concat(map1, map2, …)

Argumentai

  • map - a map

Pavyzdžiai

  • map_concat(map('1','one', '2','overridden'),map('2','two', '3','three')) → { ‚1‘: ‚one‘, ‚2‘: ‚two‘, ‚3‘: ‚three‘ }

9.2.16.7. map_delete

Returns a map with the given key and its corresponding value deleted.

Sintaksė

map_delete(map, key)

Argumentai

  • map - a map

  • key - the key to delete

Pavyzdžiai

  • map_delete(map('1','one','2','two'),'2') → { ‚1‘: ‚one‘ }

9.2.16.8. map_exist

Returns TRUE if the given key exists in the map.

Sintaksė

map_exist(map, key)

Argumentai

  • map - a map

  • key - the key to lookup

Pavyzdžiai

  • map_exist(map('1','one','2','two'),'3') → FALSE

9.2.16.9. map_get

Returns the value of a map, given its key. Returns NULL if the key does not exist.

Sintaksė

map_get(map, key)

Argumentai

  • map - a map

  • key - the key to lookup

Pavyzdžiai

  • map_get(map('1','one','2','two'),'2') → ‚two‘

  • map_get( item_variables('Map 0'), 'map_scale') → scale of the item ‚Map 0‘ (if it exists) in the current print layout

Patarimas

You can also use the index operator ([]) to get a value from a map.

9.2.16.10. map_insert

Returns a map with an added key/value. If the key already exists, its value is overridden.

Sintaksė

map_insert(map, key, value)

Argumentai

  • map - a map

  • key - the key to add

  • value - the value to add

Pavyzdžiai

  • map_insert(map('1','one'),'3','three') → { ‚1‘: ‚one‘, ‚3‘: ‚three‘ }

  • map_insert(map('1','one','2','overridden'),'2','two') → { ‚1‘: ‚one‘, ‚2‘: ‚two‘ }

9.2.16.11. map_prefix_keys

Returns a map with all keys prefixed by a given string.

Sintaksė

map_prefix_keys(map, prefix)

Argumentai

  • map - a map

  • prefix - a string

Pavyzdžiai

  • map_prefix_keys(map('1','one','2','two'), 'prefix-') → { ‚prefix-1‘: ‚one‘, ‚prefix-2‘: ‚two‘ }

9.2.16.12. map_to_hstore

Merge map elements into a hstore-formatted string.

Sintaksė

map_to_hstore(map)

Argumentai

  • map - the input map

Pavyzdžiai

  • map_to_hstore(map('1','one','2','two')) → ‚„1“=>“one“‘,‚„2“=>“two“‘

9.2.16.13. map_to_html_dl

Merge map elements into a HTML definition list string.

Sintaksė

map_to_html_dl(map)

Argumentai

  • map - the input map

Pavyzdžiai

  • map_to_html_dl(map('1','one','2','two')) → <dl><dt>1</dt><dd>one</dd><dt>2</dt><dd>two</dd></dl>

9.2.16.14. map_to_html_table

Merge map elements into a HTML table string.

Sintaksė

map_to_html_table(map)

Argumentai

  • map - the input map

Pavyzdžiai

  • map_to_html_table(map('1','one','2','two')) → <table><thead><tr><th>1</th><th>2</th></tr></thead><tbody><tr><td>one</td><td>two</td></tr></tbody></table>

9.2.16.15. to_json

Create a JSON formatted string from a map, array or other value.

Sintaksė

to_json(value)

Argumentai

  • value - The input value

Pavyzdžiai

  • to_json(map('1','one','2','two')) → {„1“:“one“,“2“:“two“}

  • to_json(array(1,2,3)) → [1,2,3]

9.2.16.16. url_encode

Returns an URL encoded string from a map. Transforms all characters in their properly-encoded form producing a fully-compliant query string.

Note that the plus sign ‚+‘ is not converted.

Sintaksė

url_encode(map)

Argumentai

  • map - a map.

Pavyzdžiai

  • url_encode(map('a&+b', 'a and plus b', 'a=b', 'a equals b')) → ‚a%26+b=a%20and%20plus%20b&a%3Db=a%20equals%20b‘

9.2.17. Mathematical Functions

This group contains math functions (e.g., square root, sin and cos).

9.2.17.1. abs

Returns the absolute value of a number.

Sintaksė

abs(value)

Argumentai

  • value - a number

Pavyzdžiai

  • abs(-2) → 2

9.2.17.2. acos

Returns the inverse cosine of a value in radians.

Sintaksė

acos(value)

Argumentai

  • value - cosine of an angle in radians

Pavyzdžiai

  • acos(0.5) → 1.0471975511966

9.2.17.3. asin

Returns the inverse sine of a value in radians.

Sintaksė

asin(value)

Argumentai

  • value - sine of an angle in radians

Pavyzdžiai

  • asin(1.0) → 1.5707963267949

9.2.17.4. atan

Returns the inverse tangent of a value in radians.

Sintaksė

atan(value)

Argumentai

  • value - tan of an angle in radians

Pavyzdžiai

  • atan(0.5) → 0.463647609000806

9.2.17.5. atan2

Returns the inverse tangent of dy/dx by using the signs of the two arguments to determine the quadrant of the result.

Sintaksė

atan2(dy, dx)

Argumentai

  • dy - y coordinate difference

  • dx - x coordinate difference

Pavyzdžiai

  • atan2(1.0, 1.732) → 0.523611477769969

9.2.17.6. ceil

Rounds a number upwards.

Sintaksė

ceil(value)

Argumentai

  • value - a number

Pavyzdžiai

  • ceil(4.9) → 5

  • ceil(-4.9) → -4

9.2.17.7. clamp

Restricts an input value to a specified range.

Sintaksė

clamp(minimum, input, maximum)

Argumentai

  • minimum - the smallest value input is allowed to take.

  • input - a value which will be restricted to the range specified by minimum and maximum

  • maximum - the largest value input is allowed to take

Pavyzdžiai

  • clamp(1,5,10) → 5

    input is between 1 and 10 so is returned unchanged

  • clamp(1,0,10) → 1

    input is less than minimum value of 1, so function returns 1

  • clamp(1,11,10) → 10

    input is greater than maximum value of 10, so function returns 10

9.2.17.8. cos

Returns cosine of an angle.

Sintaksė

cos(angle)

Argumentai

  • angle - angle in radians

Pavyzdžiai

  • cos(1.571) → 0.000796326710733263

9.2.17.9. degrees

Converts from radians to degrees.

Sintaksė

degrees(radians)

Argumentai

  • radians - numeric value

Pavyzdžiai

  • degrees(3.14159) → 180

  • degrees(1) → 57.2958

9.2.17.10. exp

Returns exponential of an value.

Sintaksė

exp(value)

Argumentai

  • value - number to return exponent of

Pavyzdžiai

  • exp(1.0) → 2.71828182845905

9.2.17.11. floor

Rounds a number downwards.

Sintaksė

floor(value)

Argumentai

  • value - a number

Pavyzdžiai

  • floor(4.9) → 4

  • floor(-4.9) → -5

9.2.17.12. ln

Returns the natural logarithm of a value.

Sintaksė

ln(value)

Argumentai

  • value - numeric value

Pavyzdžiai

  • ln(1) → 0

  • ln(2.7182818284590452354) → 1

9.2.17.13. log

Returns the value of the logarithm of the passed value and base.

Sintaksė

log(base, value)

Argumentai

  • base - any positive number

  • value - any positive number

Pavyzdžiai

  • log(2, 32) → 5

  • log(0.5, 32) → -5

9.2.17.14. log10

Returns the value of the base 10 logarithm of the passed expression.

Sintaksė

log10(value)

Argumentai

  • value - any positive number

Pavyzdžiai

  • log10(1) → 0

  • log10(100) → 2

9.2.17.15. max

Returns the largest value in a set of values.

Sintaksė

max(value1, value2, …)

Argumentai

  • value - a number

Pavyzdžiai

  • max(2,10.2,5.5) → 10.2

  • max(20.5,NULL,6.2) → 20.5

9.2.17.16. min

Returns the smallest value in a set of values.

Sintaksė

min(value1, value2, …)

Argumentai

  • value - a number

Pavyzdžiai

  • min(20.5,10,6.2) → 6.2

  • min(2,-10.3,NULL) → -10.3

9.2.17.17. pi

Returns value of pi for calculations.

Sintaksė

pi()

Pavyzdžiai

  • pi() → 3.14159265358979

9.2.17.18. radians

Converts from degrees to radians.

Sintaksė

radians(degrees)

Argumentai

  • degrees - numeric value

Pavyzdžiai

  • radians(180) → 3.14159

  • radians(57.2958) → 1

9.2.17.19. rand

Returns a random integer within the range specified by the minimum and maximum argument (inclusive). If a seed is provided, the returned will always be the same, depending on the seed.

Sintaksė

rand(min, max, [seed=NULL])

[] žymi neprivalomus argumentus

Argumentai

  • min - an integer representing the smallest possible random number desired

  • max - an integer representing the largest possible random number desired

  • seed - any value to use as seed

Pavyzdžiai

  • rand(1, 10) → 8

9.2.17.20. randf

Returns a random float within the range specified by the minimum and maximum argument (inclusive). If a seed is provided, the returned will always be the same, depending on the seed.

Sintaksė

randf([min=0.0], [max=1.0], [seed=NULL])

[] žymi neprivalomus argumentus

Argumentai

  • min - an float representing the smallest possible random number desired

  • max - an float representing the largest possible random number desired

  • seed - any value to use as seed

Pavyzdžiai

  • randf(1, 10) → 4.59258286403147

9.2.17.21. round

Rounds a number to number of decimal places.

Sintaksė

round(value, [places=0])

[] žymi neprivalomus argumentus

Argumentai

  • value - decimal number to be rounded

  • places - Optional integer representing number of places to round decimals to. Can be negative.

Pavyzdžiai

  • round(1234.567, 2) → 1234.57

  • round(1234.567) → 1235

  • round(1234.567, -1) → 1230

9.2.17.22. scale_exponential

Transforms a given value from an input domain to an output range using an exponential curve. This function can be used to ease values in or out of the specified output range.

Sintaksė

scale_exponential(value, domain_min, domain_max, range_min, range_max, exponent)

Argumentai

  • value - A value in the input domain. The function will return a corresponding scaled value in the output range.

  • domain_min - Specifies the minimum value in the input domain, the smallest value the input value should take.

  • domain_max - Specifies the maximum value in the input domain, the largest value the input value should take.

  • range_min - Specifies the minimum value in the output range, the smallest value which should be output by the function.

  • range_max - Specifies the maximum value in the output range, the largest value which should be output by the function.

  • exponent - A positive value (greater than 0), which dictates the way input values are mapped to the output range. Large exponents will cause the output values to ‚ease in‘, starting slowly before accelerating as the input values approach the domain maximum. Smaller exponents (less than 1) will cause output values to ‚ease out‘, where the mapping starts quickly but slows as it approaches the domain maximum.

Pavyzdžiai

  • scale_exponential(5,0,10,0,100,2) → 3.030

    easing in, using an exponent of 2

  • scale_exponential(3,0,10,0,100,0.5) → 87.585

    easing out, using an exponent of 0.5

9.2.17.23. scale_linear

Transforms a given value from an input domain to an output range using linear interpolation.

Sintaksė

scale_linear(value, domain_min, domain_max, range_min, range_max)

Argumentai

  • value - A value in the input domain. The function will return a corresponding scaled value in the output range.

  • domain_min - Specifies the minimum value in the input domain, the smallest value the input value should take.

  • domain_max - Specifies the maximum value in the input domain, the largest value the input value should take.

  • range_min - Specifies the minimum value in the output range, the smallest value which should be output by the function.

  • range_max - Specifies the maximum value in the output range, the largest value which should be output by the function.

Pavyzdžiai

  • scale_linear(5,0,10,0,100) → 50

  • scale_linear(0.2,0,1,0,360) → 72

    scaling a value between 0 and 1 to an angle between 0 and 360

  • scale_linear(1500,1000,10000,9,20) → 9.6111111

    scaling a population which varies between 1000 and 10000 to a font size between 9 and 20

9.2.17.24. scale_polynomial

Transforms a given value from an input domain to an output range using a polynomial curve. This function can be used to ease values in or out of the specified output range.

Sintaksė

scale_polynomial(value, domain_min, domain_max, range_min, range_max, exponent)

Argumentai

  • value - A value in the input domain. The function will return a corresponding scaled value in the output range.

  • domain_min - Specifies the minimum value in the input domain, the smallest value the input value should take.

  • domain_max - Specifies the maximum value in the input domain, the largest value the input value should take.

  • range_min - Specifies the minimum value in the output range, the smallest value which should be output by the function.

  • range_max - Specifies the maximum value in the output range, the largest value which should be output by the function.

  • exponent - A positive value (greater than 0), which dictates the way input values are mapped to the output range. Large exponents will cause the output values to ‚ease in‘, starting slowly before accelerating as the input values approach the domain maximum. Smaller exponents (less than 1) will cause output values to ‚ease out‘, where the mapping starts quickly but slows as it approaches the domain maximum.

Pavyzdžiai

  • scale_polynomial(5,0,10,0,100,2) → 25

    easing in, using an exponent of 2

  • scale_polynomial(3,0,10,0,100,0.5) → 54.772

    easing out, using an exponent of 0.5

9.2.17.25. sin

Returns the sine of an angle.

Sintaksė

sin(angle)

Argumentai

  • angle - angle in radians

Pavyzdžiai

  • sin(1.571) → 0.999999682931835

9.2.17.26. sqrt

Returns square root of a value.

Sintaksė

sqrt(value)

Argumentai

  • value - a number

Pavyzdžiai

  • sqrt(9) → 3

9.2.17.27. tan

Returns the tangent of an angle.

Sintaksė

tan(angle)

Argumentai

  • angle - angle in radians

Pavyzdžiai

  • tan(1.0) → 1.5574077246549

9.2.18. Meshes Functions

This group contains functions which calculate or return mesh related values.

9.2.18.1. $face_area

Returns the area of the current mesh face. The area calculated by this function respects both the current project’s ellipsoid setting and area unit settings. For example, if an ellipsoid has been set for the project then the calculated area will be ellipsoidal, and if no ellipsoid is set then the calculated area will be planimetric.

Sintaksė

$face_area

Pavyzdžiai

  • $face_area → 42

9.2.18.2. $face_index

Returns the index of the current mesh face.

Sintaksė

$face_index

Pavyzdžiai

  • $face_index → 4581

9.2.18.3. $vertex_as_point

Returns the current vertex as a point geometry.

Sintaksė

$vertex_as_point

Pavyzdžiai

  • geom_to_wkt( $vertex_as_point ) → ‚POINT(800 1500 41)‘

9.2.18.4. $vertex_index

Returns the index of the current mesh vertex.

Sintaksė

$vertex_index

Pavyzdžiai

  • $vertex_index → 9874

9.2.18.5. $vertex_x

Returns the X coordinate of the current mesh vertex.

Sintaksė

$vertex_x

Pavyzdžiai

  • $vertex_x → 42.12

9.2.18.6. $vertex_y

Returns the Y coordinate of the current mesh vertex.

Sintaksė

$vertex_y

Pavyzdžiai

  • $vertex_y → 12.24

9.2.18.7. $vertex_z

Returns the Z value of the current mesh vertex.

Sintaksė

$vertex_z

Pavyzdžiai

  • $vertex_z → 42

9.2.19. Operators

This group contains operators (e.g., +, -, *). Note that for most of the mathematical functions below, if one of the inputs is NULL then the result is NULL.

9.2.19.1. %

Remainder of division. Takes the sign of the dividend.

Sintaksė

a % b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 9 % 2 → 1

  • 9 % -2 → 1

  • -9 % 2 → -1

  • 5 % NULL → NULL

9.2.19.2. *

Multiplication of two values

Sintaksė

a * b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 * 4 → 20

  • 5 * NULL → NULL

9.2.19.3. +

Addition of two values. If one of the values is NULL the result will be NULL.

Sintaksė

a + b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 + 4 → 9

  • 5 + NULL → NULL

  • 'QGIS ' + 'ROCKS' → ‚QGIS ROCKS‘

  • to_datetime('2020-08-01 12:00:00') + '1 day 2 hours' → 2020-08-02T14:00:00

Further reading: concat, ||

9.2.19.4. -

Subtraction of two values. If one of the values is NULL the result will be NULL.

Sintaksė

a - b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 - 4 → 1

  • 5 - NULL → NULL

  • to_datetime('2012-05-05 12:00:00') - to_interval('1 day 2 hours') → 2012-05-04T10:00:00

9.2.19.5. /

Division of two values

Sintaksė

a / b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 / 4 → 1.25

  • 5 / NULL → NULL

9.2.19.6. //

Floor division of two values

Sintaksė

a // b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 9 // 2 → 4

9.2.19.7. <

Compares two values and evaluates to 1 if the left value is less than the right value.

Sintaksė

a < b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 < 4 → FALSE

  • 5 < 5 → FALSE

  • 4 < 5 → TRUE

9.2.19.8. <=

Compares two values and evaluates to 1 if the left value is less or equal than the right value.

Sintaksė

a <= b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 <= 4 → FALSE

  • 5 <= 5 → TRUE

  • 4 <= 5 → TRUE

9.2.19.9. <>

Compares two values and evaluates to 1 if they are not equal.

Sintaksė

a <> b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 <> 4 → TRUE

  • 4 <> 4 → FALSE

  • 5 <> NULL → NULL

  • NULL <> NULL → NULL

9.2.19.10. =

Compares two values and evaluates to 1 if they are equal.

Sintaksė

a = b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 = 4 → FALSE

  • 4 = 4 → TRUE

  • 5 = NULL → NULL

  • NULL = NULL → NULL

9.2.19.11. >

Compares two values and evaluates to 1 if the left value is greater than the right value.

Sintaksė

a > b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 > 4 → TRUE

  • 5 > 5 → FALSE

  • 4 > 5 → FALSE

9.2.19.12. >=

Compares two values and evaluates to 1 if the left value is greater or equal than the right value.

Sintaksė

a >= b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 >= 4 → TRUE

  • 5 >= 5 → TRUE

  • 4 >= 5 → FALSE

9.2.19.13. AND

Returns TRUE when conditions a and b are true.

Sintaksė

a AND b

Argumentai

  • a - condition

  • b - condition

Pavyzdžiai

  • TRUE AND TRUE → TRUE

  • TRUE AND FALSE → FALSE

  • 4 = 2+2 AND 1 = 1 → TRUE

  • 4 = 2+2 AND 1 = 2 → FALSE

9.2.19.14. BETWEEN

Returns TRUE if value is within the specified range. The range is considered inclusive of the bounds. To test for exclusion NOT BETWEEN can be used.

Sintaksė

value BETWEEN lower_bound AND higher_bound

Argumentai

  • value - the value to compare with a range. It can be a string, a number or a date.

  • lower_bound AND higher_bound - range bounds

Pavyzdžiai

  • 'B' BETWEEN 'A' AND 'C' → TRUE

  • 2 BETWEEN 1 AND 3 → TRUE

  • 2 BETWEEN 2 AND 3 → TRUE

  • 'B' BETWEEN 'a' AND 'c' → FALSE

  • lower('B') BETWEEN 'a' AND 'b' → TRUE

Pastaba

value BETWEEN lower_bound AND higher_bound is the same as „value >= lower_bound AND value <= higher_bound“.

Further reading: NOT BETWEEN

9.2.19.15. ILIKE

Returns TRUE if the first parameter matches case-insensitive the supplied pattern. LIKE can be used instead of ILIKE to make the match case-sensitive. Works with numbers also.

Sintaksė

string/number ILIKE pattern

Argumentai

  • string/number - string to search

  • pattern - pattern to find, you can use ‚%‘ as a wildcard, ‚_‘ as a single char and ‚\\‘ to escape these special characters.

Pavyzdžiai

  • 'A' ILIKE 'A' → TRUE

  • 'A' ILIKE 'a' → TRUE

  • 'A' ILIKE 'B' → FALSE

  • 'ABC' ILIKE 'b' → FALSE

  • 'ABC' ILIKE 'B' → FALSE

  • 'ABC' ILIKE '_b_' → TRUE

  • 'ABC' ILIKE '_B_' → TRUE

  • 'ABCD' ILIKE '_b_' → FALSE

  • 'ABCD' ILIKE '_B_' → FALSE

  • 'ABCD' ILIKE '_b%' → TRUE

  • 'ABCD' ILIKE '_B%' → TRUE

  • 'ABCD' ILIKE '%b%' → TRUE

  • 'ABCD' ILIKE '%B%' → TRUE

  • 'ABCD%' ILIKE 'abcd\\%' → TRUE

  • 'ABCD' ILIKE '%B\\%' → FALSE

9.2.19.16. IN

Returns TRUE if value is found within a list of values.

Sintaksė

a IN b

Argumentai

  • a - value

  • b - list of values

Pavyzdžiai

  • 'A' IN ('A','B') → TRUE

  • 'A' IN ('C','B') → FALSE

9.2.19.17. IS

Returns TRUE if a is the same as b.

Sintaksė

a IS b

Argumentai

  • a - any value

  • b - any value

Pavyzdžiai

  • 'A' IS 'A' → TRUE

  • 'A' IS 'a' → FALSE

  • 4 IS 4 → TRUE

  • 4 IS 2+2 → TRUE

  • 4 IS 2 → FALSE

  • @geometry IS NULL → 0, if your geometry is not NULL

9.2.19.18. IS NOT

Returns TRUE if a is not the same as b.

Sintaksė

a IS NOT b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 'a' IS NOT 'b' → TRUE

  • 'a' IS NOT 'a' → FALSE

  • 4 IS NOT 2+2 → FALSE

9.2.19.19. LIKE

Returns TRUE if the first parameter matches the supplied pattern. Works with numbers also.

Sintaksė

string/number LIKE pattern

Argumentai

  • string/number - value

  • pattern - pattern to compare value with, you can use ‚%‘ as a wildcard, ‚_‘ as a single char and ‚\\‘ to escape these special characters.

Pavyzdžiai

  • 'A' LIKE 'A' → TRUE

  • 'A' LIKE 'a' → FALSE

  • 'A' LIKE 'B' → FALSE

  • 'ABC' LIKE 'B' → FALSE

  • 'ABC' LIKE '_B_' → TRUE

  • 'ABCD' LIKE '_B_' → FALSE

  • 'ABCD' LIKE '_B%' → TRUE

  • 'ABCD' LIKE '%B%' → TRUE

  • '1%' LIKE '1\\%' → TRUE

  • '1_' LIKE '1\\%' → FALSE

9.2.19.20. NOT

Negates a condition.

Sintaksė

NOT a

Argumentai

  • a - condition

Pavyzdžiai

  • NOT 1 → FALSE

  • NOT 0 → TRUE

9.2.19.21. NOT BETWEEN

Returns TRUE if value is not within the specified range. The range is considered inclusive of the bounds.

Sintaksė

value NOT BETWEEN lower_bound AND higher_bound

Argumentai

  • value - the value to compare with a range. It can be a string, a number or a date.

  • lower_bound AND higher_bound - range bounds

Pavyzdžiai

  • 'B' NOT BETWEEN 'A' AND 'C' → FALSE

  • 1.0 NOT BETWEEN 1.1 AND 1.2 → TRUE

  • 2 NOT BETWEEN 2 AND 3 → FALSE

  • 'B' NOT BETWEEN 'a' AND 'c' → TRUE

  • lower('B') NOT BETWEEN 'a' AND 'b' → FALSE

Pastaba

value NOT BETWEEN lower_bound AND higher_bound is the same as „value < lower_bound OR value > higher_bound“.

Further reading: BETWEEN

9.2.19.22. OR

Returns TRUE when condition a or b is true.

Sintaksė

a OR b

Argumentai

  • a - condition

  • b - condition

Pavyzdžiai

  • 4 = 2+2 OR 1 = 1 → TRUE

  • 4 = 2+2 OR 1 = 2 → TRUE

  • 4 = 2   OR 1 = 2 → FALSE

9.2.19.23. []

Index operator. Returns an element from an array or map value.

Sintaksė

[index]

Argumentai

  • index - array index or map key value

Pavyzdžiai

  • array(1,2,3)[0] → 1

  • array(1,2,3)[2] → 3

  • array(1,2,3)[-1] → 3

  • map('a',1,'b',2)['a'] → 1

  • map('a',1,'b',2)['b'] → 2

Further reading: array_get, map_get

9.2.19.24. ^

Power of two values.

Sintaksė

a ^ b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 5 ^ 4 → 625

  • 5 ^ NULL → NULL

9.2.19.25. ||

Joins two values together into a string.

If one of the values is NULL the result will be NULL. See the CONCAT function for a different behavior.

Sintaksė

a || b

Argumentai

  • a - value

  • b - value

Pavyzdžiai

  • 'Here' || ' and ' || 'there' → ‚Here and there‘

  • 'Nothing' || NULL → NULL

  • 'Dia: ' || "Diameter" → ‚Dia: 25‘

  • 1 || 2 → ‚12‘

Further reading: concat, +

9.2.19.26. ~

Performs a regular expression match on a string value. Backslash characters must be double escaped (e.g., „\\s“ to match a white space character).

Sintaksė

string ~ regex

Argumentai

  • string - A string value

  • regex - A regular expression. Slashes must be escaped, eg \\d.

Pavyzdžiai

  • 'hello' ~ 'll' → TRUE

  • 'hello' ~ '^ll' → FALSE

  • 'hello' ~ 'llo$' → TRUE

  • 'abc123' ~ '\\d+' → TRUE

Further reading: regexp_match

9.2.20. Processing Functions

This group contains functions that operate on processing algorithms.

9.2.20.1. parameter

Returns the value of a processing algorithm input parameter.

Sintaksė

parameter(name)

Argumentai

  • name - name of the corresponding input parameter

Pavyzdžiai

  • parameter('BUFFER_SIZE') → 5.6

9.2.21. Rasters Functions

This group contains functions to operate on raster layer.

9.2.21.1. raster_attributes

Returns a map with the fields names as keys and the raster attribute table values as values from the attribute table entry that matches the given raster value.

Sintaksė

raster_attributes(layer, band, value)

Argumentai

  • layer - the name or id of a raster layer

  • band - the band number for the associated attribute table lookup.

  • value - raster value

Pavyzdžiai

  • raster_attributes('vegetation', 1, raster_value('vegetation', 1, make_point(1,1))) → {‚class‘: ‚Vegetated‘, ‚subclass‘: ‚Trees‘}

  • raster_attributes('vegetation', 1, raster_value('vegetation', 1, @layer_cursor_point)) → {‚class‘: ‚Vegetated‘, ‚subclass‘: ‚Trees‘}

9.2.21.2. raster_statistic

Returns statistics from a raster layer.

Sintaksė

raster_statistic(layer, band, property)

Argumentai

  • layer - a string, representing either a raster layer name or layer ID

  • band - integer representing the band number from the raster layer, starting at 1

  • property - a string corresponding to the property to return. Valid options are:

    • min: minimum value

    • max: maximum value

    • avg: average (mean) value

    • stdev: standard deviation of values

    • range: range of values (max - min)

    • sum: sum of all values from raster

Pavyzdžiai

  • raster_statistic('lc',1,'avg') → Average value from band 1 from ‚lc‘ raster layer

  • raster_statistic('ac2010',3,'min') → Minimum value from band 3 from ‚ac2010‘ raster layer

9.2.21.3. raster_value

Returns the raster value found at the provided point.

Sintaksė

raster_value(layer, band, point)

Argumentai

  • layer - the name or id of a raster layer

  • band - the band number to sample the value from.

  • point - point geometry (for multipart geometries having more than one part, a NULL value will be returned)

Pavyzdžiai

  • raster_value('dem', 1, make_point(1,1)) → 25

  • raster_value('ndvi', 2, @layer_cursor_point) → 25

9.2.22. Record and Attributes Functions

This group contains functions that operate on record identifiers.

9.2.22.1. attribute

Returns an attribute from a feature.

Variant 1

Returns the value of an attribute from the current feature.

Sintaksė

attribute(attribute_name)

Argumentai

  • attribute_name - name of attribute to be returned

Pavyzdžiai

  • attribute( 'name' ) → value stored in ‚name‘ attribute for the current feature

Variant 2

Allows the target feature and attribute name to be specified.

Sintaksė

attribute(feature, attribute_name)

Argumentai

  • feature - a feature

  • attribute_name - name of attribute to be returned

Pavyzdžiai

  • attribute( @atlas_feature, 'name' ) → value stored in ‚name‘ attribute for the current atlas feature

9.2.22.2. attributes

Returns a map containing all attributes from a feature, with field names as map keys.

Variant 1

Returns a map of all attributes from the current feature.

Sintaksė

attributes()

Pavyzdžiai

  • attributes()['name'] → value stored in ‚name‘ attribute for the current feature

Variant 2

Allows the target feature to be specified.

Sintaksė

attributes(feature)

Argumentai

  • feature - a feature

Pavyzdžiai

  • attributes( @atlas_feature )['name'] → value stored in ‚name‘ attribute for the current atlas feature

Further reading: Maps Functions

9.2.22.3. $currentfeature

Returns the current feature being evaluated. This can be used with the ‚attribute‘ function to evaluate attribute values from the current feature. WARNING: This function is deprecated. It is recommended to use the replacement @feature variable instead.

Sintaksė

$currentfeature

Pavyzdžiai

  • attribute( $currentfeature, 'name' ) → value stored in ‚name‘ attribute for the current feature

9.2.22.4. display_expression

Returns the display expression for a given feature in a layer. The expression is evaluated by default. Can be used with zero, one or more arguments, see below for details.

No parameters

If called with no parameters, the function will evaluate the display expression of the current feature in the current layer.

Sintaksė

display_expression()

Pavyzdžiai

  • display_expression() → The display expression of the current feature in the current layer.

One ‚feature‘ parameter

If called with a ‚feature‘ parameter only, the function will evaluate the specified feature from the current layer.

Sintaksė

display_expression(feature)

Argumentai

  • feature - The feature which should be evaluated.

Pavyzdžiai

  • display_expression(@atlas_feature) → The display expression of the current atlas feature.

Layer and feature parameters

If the function is called with both a layer and a feature, it will evaluate the specified feature from the specified layer.

Sintaksė

display_expression(layer, feature, [evaluate=true])

[] žymi neprivalomus argumentus

Argumentai

  • layer - The layer (or its ID or name)

  • feature - The feature which should be evaluated.

  • evaluate - If the expression must be evaluated. If false, the expression will be returned as a string literal only (which could potentially be later evaluated using the ‚eval‘ function).

Pavyzdžiai

  • display_expression( 'streets', get_feature_by_id('streets', 1)) → The display expression of the feature with the ID 1 on the layer ‚streets‘.

  • display_expression('a_layer_id', @feature, 'False') → The display expression of the given feature not evaluated.

9.2.22.5. feature_id

Returns a feature’s unique ID, or NULL if the feature is not valid.

Sintaksė

feature_id(feature)

Argumentai

  • feature - a feature object

Pavyzdžiai

  • feature_id( @feature ) → the ID of the current feature

Further reading: get_feature_by_id

9.2.22.6. get_feature

Returns the first feature of a layer matching a given attribute value.

Single value variant

Along with the layer ID, a single column and value are specified.

Sintaksė

get_feature(layer, attribute, value)

Argumentai

  • layer - layer name or ID

  • attribute - attribute name to use for the match

  • value - attribute value to match

Pavyzdžiai

  • get_feature('streets','name','main st') → first feature found in „streets“ layer with „main st“ value in the „name“ field

Map variant

Along with the layer ID, a map containing the columns (key) and their respective value to be used.

Sintaksė

get_feature(layer, attribute)

Argumentai

  • layer - layer name or ID

  • attribute - Map containing the column and value pairs to use

Pavyzdžiai

  • get_feature('streets',map('name','main st','lane_num','4')) → first feature found in „streets“ layer with „main st“ value in the „name“ field and „4“ value in the „lane_num“ field

9.2.22.7. get_feature_by_id

Returns the feature with an id on a layer.

Sintaksė

get_feature_by_id(layer, feature_id)

Argumentai

  • layer - layer, layer name or layer id

  • feature_id - the id of the feature which should be returned

Pavyzdžiai

  • get_feature_by_id('streets', 1) → the feature with the id 1 on the layer „streets“

Further reading: feature_id

9.2.22.8. $id

Returns the feature id of the current row. WARNING: This function is deprecated. It is recommended to use the replacement @id variable instead.

Sintaksė

$id

Pavyzdžiai

  • $id → 42

Further reading: feature_id, get_feature_by_id

9.2.22.9. is_attribute_valid

Returns TRUE if a specific feature attribute meets all constraints.

Sintaksė

is_attribute_valid(attribute, [feature], [layer], [strength])

[] žymi neprivalomus argumentus

Argumentai

  • attribute - an attribute name

  • feature - A feature. If not set, the current feature will be used.

  • layer - A vector layer. If not set, the current layer will be used.

  • strength - Set to ‚hard‘ or ‚soft‘ to narrow down to a specific constraint type. If not set, the function will return FALSE if either a hard or a soft constraint fails.

Pavyzdžiai

  • is_attribute_valid('HECTARES') → TRUE if the current feature’s value in the „HECTARES“ field meets all constraints.

  • is_attribute_valid('HOUSES',get_feature('my_layer', 'FID', 10), 'my_layer') → FALSE if the value in the „HOUSES“ field from the feature with „FID“=10 in ‚my_layer‘ fails to meet all constraints.

Further reading: Constraints

9.2.22.10. is_feature_valid

Returns TRUE if a feature meets all field constraints.

Sintaksė

is_feature_valid([feature], [layer], [strength])

[] žymi neprivalomus argumentus

Argumentai

  • feature - A feature. If not set, the current feature will be used.

  • layer - A vector layer. If not set, the current layer will be used.

  • strength - Set to ‚hard‘ or ‚soft‘ to narrow down to a specific constraint type. If not set, the function will return FALSE if either a hard or a soft constraint fails.

Pavyzdžiai

  • is_feature_valid(strength:='hard') → TRUE if all fields from the current feature meet their hard constraints.

  • is_feature_valid(get_feature('my_layer', 'FID', 10), 'my_layer') → FALSE if all fields from feature with „FID“=10 in ‚my_layer‘ fails to meet all constraints.

Further reading: Constraints

9.2.22.11. is_selected

Returns TRUE if a feature is selected. Can be used with zero, one or two arguments, see below for details.

No parameters

If called with no parameters, the function will return TRUE if the current feature in the current layer is selected.

Sintaksė

is_selected()

Pavyzdžiai

  • is_selected() → TRUE if the current feature in the current layer is selected.

One ‚feature‘ parameter

If called with a ‚feature‘ parameter only, the function returns TRUE if the specified feature from the current layer is selected.

Sintaksė

is_selected(feature)

Argumentai

  • feature - The feature which should be checked for selection.

Pavyzdžiai

  • is_selected(@atlas_feature) → TRUE if the current atlas feature is selected.

  • is_selected(get_feature('streets', 'name', 'Main St.')) → TRUE if the unique named „Main St.“ feature on the active „streets“ layer is selected.

  • is_selected(get_feature_by_id('streets', 1)) → TRUE if the feature with the id 1 on the active „streets“ layer is selected.

Two parameters

If the function is called with both a layer and a feature, it will return TRUE if the specified feature from the specified layer is selected.

Sintaksė

is_selected(layer, feature)

Argumentai

  • layer - The layer (its ID or name) on which the selection will be checked.

  • feature - The feature which should be checked for selection.

Pavyzdžiai

  • is_selected( 'streets', get_feature('streets', 'name', "street_name")) → TRUE if the current building’s street is selected (assuming the building layer has a field named ‚street_name‘ and the ‚streets‘ layer has a field called ‚name‘ with unique values).

  • is_selected( 'streets', get_feature_by_id('streets', 1)) → TRUE if the feature with the id 1 on the „streets“ layer is selected.

9.2.22.12. maptip

Returns the maptip for a given feature in a layer. The expression is evaluated by default. Can be used with zero, one or more arguments, see below for details.

No parameters

If called with no parameters, the function will evaluate the maptip of the current feature in the current layer.

Sintaksė

maptip()

Pavyzdžiai

  • maptip() → The maptip of the current feature in the current layer.

One ‚feature‘ parameter

If called with a ‚feature‘ parameter only, the function will evaluate the specified feature from the current layer.

Sintaksė

maptip(feature)

Argumentai

  • feature - The feature which should be evaluated.

Pavyzdžiai

  • maptip(@atlas_feature) → The maptip of the current atlas feature.

Layer and feature parameters

If the function is called with both a layer and a feature, it will evaluate the specified feature from the specified layer.

Sintaksė

maptip(layer, feature, [evaluate=true])

[] žymi neprivalomus argumentus

Argumentai

  • layer - The layer (or its ID or name)

  • feature - The feature which should be evaluated.

  • evaluate - If the expression must be evaluated. If false, the expression will be returned as a string literal only (which could potentially be later evaluated using the ‚eval_template‘ function).

Pavyzdžiai

  • maptip('streets', get_feature_by_id('streets', 1)) → The maptip of the feature with the ID 1 on the layer ‚streets‘.

  • maptip('a_layer_id', @feature, 'False') → The maptip of the given feature not evaluated.

9.2.22.13. num_selected

Returns the number of selected features on a given layer. By default works on the layer on which the expression is evaluated.

Sintaksė

num_selected([layer=current layer])

[] žymi neprivalomus argumentus

Argumentai

  • layer - The layer (or its id or name) on which the selection will be checked.

Pavyzdžiai

  • num_selected() → The number of selected features on the current layer.

  • num_selected('streets') → The number of selected features on the layer streets

9.2.22.14. represent_attributes

Returns a map with the attribute names as keys and the configured representation values as values. The representation value for the attributes depends on the configured widget type for each attribute. Can be used with zero, one or more arguments, see below for details.

No parameters

If called with no parameters, the function will return the representation of the attributes of the current feature in the current layer.

Sintaksė

represent_attributes()

Pavyzdžiai

  • represent_attributes() → The representation of the attributes for the current feature.

One ‚feature‘ parameter

If called with a ‚feature‘ parameter only, the function will return the representation of the attributes of the specified feature from the current layer.

Sintaksė

represent_attributes(feature)

Argumentai

  • feature - The feature which should be evaluated.

Pavyzdžiai

  • represent_attributes(@atlas_feature) → The representation of the attributes for the specified feature from the current layer.

Layer and feature parameters

If called with a ‚layer‘ and a ‚feature‘ parameter, the function will return the representation of the attributes of the specified feature from the specified layer.

Sintaksė

represent_attributes(layer, feature)

Argumentai

  • layer - The layer (or its ID or name).

  • feature - The feature which should be evaluated.

Pavyzdžiai

  • represent_attributes('atlas_layer', @atlas_feature) → The representation of the attributes for the specified feature from the specified layer.

Further reading: represent_value

9.2.22.15. represent_value

Returns the configured representation value for a field value. It depends on the configured widget type. Often, this is useful for ‚Value Map‘ widgets.

Sintaksė

represent_value(value, [fieldName])

[] žymi neprivalomus argumentus

Argumentai

  • value - The value which should be resolved. Most likely a field.

  • fieldName - The field name for which the widget configuration should be loaded.

Pavyzdžiai

  • represent_value("field_with_value_map") → Description for value

  • represent_value('static value', 'field_name') → Description for static value

Further reading: widget types, represent_attributes

9.2.22.16. sqlite_fetch_and_increment

Manage autoincrementing values in sqlite databases.

SQlite default values can only be applied on insert and not prefetched.

This makes it impossible to acquire an incremented primary key via AUTO_INCREMENT before creating the row in the database. Sidenote: with postgres, this works via the option evaluate default values.

When adding new features with relations, it is really nice to be able to already add children for a parent, while the parents form is still open and hence the parent feature uncommitted.

To get around this limitation, this function can be used to manage sequence values in a separate table on sqlite based formats like gpkg.

The sequence table will be filtered for a sequence id (filter_attribute and filter_value) and the current value of the id_field will be incremented by 1 and the incremented value returned.

If additional columns require values to be specified, the default_values map can be used for this purpose.

Note

This function modifies the target sqlite table. It is intended for usage with default value configurations for attributes.

When the database parameter is a layer and the layer is in transaction mode, the value will only be retrieved once during the lifetime of a transaction and cached and incremented. This makes it unsafe to work on the same database from several processes in parallel.

Sintaksė

sqlite_fetch_and_increment(database, table, id_field, filter_attribute, filter_value, [default_values])

[] žymi neprivalomus argumentus

Argumentai

  • database - Path to the sqlite file or geopackage layer

  • table - Name of the table that manages the sequences

  • id_field - Name of the field that contains the current value

  • filter_attribute - Name the field that contains a unique identifier for this sequence. Must have a UNIQUE index.

  • filter_value - Name of the sequence to use.

  • default_values - Map with default values for additional columns on the table. The values need to be fully quoted. Functions are allowed.

Pavyzdžiai

  • sqlite_fetch_and_increment(@layer, 'sequence_table', 'last_unique_id', 'sequence_id', 'global', map('last_change', 'date(''now'')', 'user', '''' || @user_account_name || '''')) → 0

  • sqlite_fetch_and_increment(layer_property(@layer, 'path'), 'sequence_table', 'last_unique_id', 'sequence_id', 'global', map('last_change', 'date(''now'')', 'user', '''' || @user_account_name || '''')) → 0

Further reading: Duomenų šaltinių savybės, Setting relations between multiple layers

9.2.22.17. uuid

Generates a Universally Unique Identifier (UUID) for each row using the Qt QUuid::createUuid method.

Sintaksė

uuid([format=‘WithBraces‘])

[] žymi neprivalomus argumentus

Argumentai

  • format - The format, as the UUID will be formatted. ‚WithBraces‘, ‚WithoutBraces‘ or ‚Id128‘.

Pavyzdžiai

  • uuid() → ‚{0bd2f60f-f157-4a6d-96af-d4ba4cb366a1}‘

  • uuid('WithoutBraces') → ‚0bd2f60f-f157-4a6d-96af-d4ba4cb366a1‘

  • uuid('Id128') → ‚0bd2f60ff1574a6d96afd4ba4cb366a1‘

9.2.23. Relations

This group contains the list of the relations available in the current project, with their description. It provides a quick access to the relation ID for writing an expression (with e.g. the relation_aggregate function) or customizing a form.

9.2.24. Sensors Functions

This group contains functions to interact with sensors.

9.2.24.1. sensor_data

Returns the last captured value (or values as a map for sensors which report multiple values) from a registered sensor.

Sintaksė

sensor_data(name, [expiration])

[] žymi neprivalomus argumentus

Argumentai

  • name - the sensor name

  • expiration - maximum millisecond since last captured value allowed

Pavyzdžiai

  • sensor_data('geiger_1') → ‚2000‘

9.2.25. String Functions

This group contains functions that operate on strings (e.g., that replace, convert to upper case).

9.2.25.1. ascii

Returns the unicode code associated with the first character of a string.

Sintaksė

ascii(string)

Argumentai

  • string - the string to convert to unicode code

Pavyzdžiai

  • ascii('Q') → 81

9.2.25.2. char

Returns the character associated with a unicode code.

Sintaksė

char(code)

Argumentai

  • code - a unicode code number

Pavyzdžiai

  • char(81) → ‚Q‘

9.2.25.3. concat

Concatenates several strings to one. NULL values are converted to empty strings. Other values (like numbers) are converted to strings.

Sintaksė

concat(string1, string2, …)

Argumentai

  • string - a string value

Pavyzdžiai

  • concat('sun', 'set') → ‚sunset‘

  • concat('a','b','c','d','e') → ‚abcde‘

  • concat('Anno ', 1984) → ‚Anno 1984‘

  • concat('The Wall', NULL) → ‚The Wall‘

About fields concatenation

You can also concatenate strings or field values using either || or + operators, with some special characteristics:

  • The + operator also means sum up expression, so if you have an integer (field or numeric value) operand, this can be error prone and you better use the others:

    'My feature id is: ' + "gid" => triggers an error as gid returns an integer
    
  • When any of the arguments is a NULL value, either || or + will return a NULL value. To return the other arguments regardless the NULL value, you may want to use the concat or array_to_string function:

    'My feature id is: ' + NULL ==> NULL
    'My feature id is: ' || NULL => NULL
    concat('My feature id is: ', NULL) => 'My feature id is: '
    array_to_string( array('My feature id is: ', NULL) ) => 'My feature id is: '
    

further reading: array_to_string, ||, +

9.2.25.4. format

Format a string using supplied arguments.

Sintaksė

format(string, arg1, arg2, …)

Argumentai

  • string - A string with placeholders %1, %2, etc., for the arguments. Placeholders can be repeated. The lowest numbered placeholder is replaced by arg1, the next by arg2, etc.

  • arg - any type. Any number of arguments.

Pavyzdžiai

  • format('This %1 a %2','is', 'test') → ‚This is a test‘

  • format('This is %2','a bit unexpected but 2 is lowest number in string','normal') → ‚This is a bit unexpected but 2 is lowest number in string‘

9.2.25.5. format_date

Formats a date type or string into a custom string format. Uses Qt date/time format strings. See QDateTime::toString.

Sintaksė

format_date(datetime, format, [language])

[] žymi neprivalomus argumentus

Argumentai

  • datetime - date, time or datetime value

  • format - String template used to format the string.

    Expression

    Output

    d

    the day as number without a leading zero (1 to 31)

    dd

    the day as number with a leading zero (01 to 31)

    ddd

    the abbreviated localized day name (e.g. ‚Mon‘ to ‚Sun‘)

    dddd

    the long localized day name (e.g. ‚Monday‘ to ‚Sunday‘)

    M

    the month as number without a leading zero (1-12)

    MM

    the month as number with a leading zero (01-12)

    MMM

    the abbreviated localized month name (e.g. ‚Jan‘ to ‚Dec‘)

    MMMM

    the long localized month name (e.g. ‚January‘ to ‚December‘)

    yy

    the year as two digit number (00-99)

    yyyy

    the year as four digit number

    These expressions may be used for the time part of the format string:

    Expression

    Output

    h

    the hour without a leading zero (0 to 23 or 1 to 12 if AM/PM display)

    hh

    the hour with a leading zero (00 to 23 or 01 to 12 if AM/PM display)

    H

    the hour without a leading zero (0 to 23, even with AM/PM display)

    HH

    the hour with a leading zero (00 to 23, even with AM/PM display)

    m

    the minute without a leading zero (0 to 59)

    mm

    the minute with a leading zero (00 to 59)

    s

    the second without a leading zero (0 to 59)

    ss

    the second with a leading zero (00 to 59)

    z

    the milliseconds without trailing zeroes (0 to 999)

    zzz

    the milliseconds with trailing zeroes (000 to 999)

    AP or A

    interpret as an AM/PM time. AP must be either ‚AM‘ or ‚PM‘.

    ap or a

    Interpret as an AM/PM time. ap must be either ‚am‘ or ‚pm‘.

  • language - language (lowercase, two- or three-letter, ISO 639 language code) used to format the date into a custom string. By default the current QGIS user locale is used.

Pavyzdžiai

  • format_date('2012-05-15','dd.MM.yyyy') → ‚15.05.2012‘

  • format_date('2012-05-15','d MMMM yyyy','fr') → ‚15 mai 2012‘

  • format_date('2012-05-15','dddd') → ‚Tuesday‘, if the current locale is an English variant

  • format_date('2012-05-15 13:54:20','dd.MM.yy') → ‚15.05.12‘

  • format_date('13:54:20','hh:mm AP') → ‚01:54 PM‘

9.2.25.6. format_number

Returns a number formatted with the locale separator for thousands. By default the current QGIS user locale is used. Also truncates the decimal places to the number of supplied places.

Sintaksė

format_number(number, [places=0], [language], [omit_group_separators=false], [trim_trailing_zeroes=false])

[] žymi neprivalomus argumentus

Argumentai

  • number - number to be formatted

  • places - integer representing the number of decimal places to truncate the string to.

  • language - language (lowercase, two- or three-letter, ISO 639 language code) used to format the number into a string. By default the current QGIS user locale is used.

  • omit_group_separators - if set to true then group separators will not be included in the string

  • trim_trailing_zeroes - if set to true then trailing zeros following the decimal point will be trimmed from the string

Pavyzdžiai

  • format_number(10000000.332,2) → ‚10,000,000.33‘ if e.g. the current locale is an English variant

  • format_number(10000000.332,2,'fr') → ‚10 000 000,33‘

9.2.25.7. left

Returns a substring that contains the n leftmost characters of the string.

Sintaksė

left(string, length)

Argumentai

  • string - a string

  • length - integer. The number of characters from the left of the string to return.

Pavyzdžiai

  • left('Hello World',5) → ‚Hello‘

Further reading: right

9.2.25.8. length

Returns the number of characters in a string or the length of a geometry linestring.

String variant

Returns the number of characters in a string.

Sintaksė

length(string)

Argumentai

  • string - string to count length of

Pavyzdžiai

  • length('hello') → 5

Geometry variant

Calculate the length of a geometry line object. Calculations are always planimetric in the Spatial Reference System (SRS) of this geometry, and the units of the returned length will match the units for the SRS. This differs from the calculations performed by the $length function, which will perform ellipsoidal calculations based on the project’s ellipsoid and distance unit settings.

Sintaksė

length(geometry)

Argumentai

  • geometry - line geometry object

Pavyzdžiai

  • length(geom_from_wkt('LINESTRING(0 0, 4 0)')) → 4.0

9.2.25.9. lower

Converts a string to lower case letters.

Sintaksė

lower(string)

Argumentai

  • string - the string to convert to lower case

Pavyzdžiai

  • lower('HELLO World') → ‚hello world‘

Further reading: upper, title

9.2.25.10. lpad

Returns a string padded on the left to the specified width, using a fill character. If the target width is smaller than the string’s length, the string is truncated.

Sintaksė

lpad(string, width, fill)

Argumentai

  • string - string to pad

  • width - length of new string

  • fill - character to pad the remaining space with

Pavyzdžiai

  • lpad('Hello', 10, 'x') → ‚xxxxxHello‘

  • lpad('Hello', 3, 'x') → ‚Hel‘

Further reading: rpad

9.2.25.11. ltrim

Removes the longest string containing only the specified characters (a space by default) from the start of string.

Sintaksė

ltrim(string, [characters=‘ ‚])

[] žymi neprivalomus argumentus

Argumentai

  • string - string to trim

  • characters - characters to trim

Pavyzdžiai

  • ltrim('   hello world  ') → ‚hello world ‚

  • ltrim('zzzytest', 'xyz') → ‚test‘

Further reading: rtrim, trim

9.2.25.12. regexp_match

Return the first matching position matching a regular expression within an unicode string, or 0 if the substring is not found.

Sintaksė

regexp_match(input_string, regex)

Argumentai

  • input_string - the string to test against the regular expression

  • regex - The regular expression to test against. Backslash characters must be double escaped (e.g., „\\s“ to match a white space character or „\\b“ to match a word boundary).

Pavyzdžiai

  • regexp_match('QGIS ROCKS','\\sROCKS') → 5

  • regexp_match('Budač','udač\\b') → 2

Further reading: strpos

9.2.25.13. regexp_replace

Returns a string with the supplied regular expression replaced.

Sintaksė

regexp_replace(input_string, regex, replacement)

Argumentai

  • input_string - the string to replace matches in

  • regex - The regular expression to replace. Backslash characters must be double escaped (e.g., „\\s“ to match a white space character).

  • replacement - The string that will replace any matching occurrences of the supplied regular expression. Captured groups can be inserted into the replacement string using \\1, \\2, etc.

Pavyzdžiai

  • regexp_replace('QGIS SHOULD ROCK','\\sSHOULD\\s',' DOES ') → ‚QGIS DOES ROCK‘

  • regexp_replace('ABC123','\\d+','') → ‚ABC‘

  • regexp_replace('my name is John','(.*) is (.*)','\\2 is \\1') → ‚John is my name‘

Further reading: replace, array_replace

9.2.25.14. regexp_substr

Returns the portion of a string which matches a supplied regular expression.

Sintaksė

regexp_substr(input_string, regex)

Argumentai

  • input_string - the string to find matches in

  • regex - The regular expression to match against. Backslash characters must be double escaped (e.g., „\\s“ to match a white space character).

Pavyzdžiai

  • regexp_substr('abc123','(\\d+)') → ‚123‘

Further reading: substr, regexp_matches

9.2.25.15. replace

Returns a string with the supplied string, array, or map of strings replaced.

String & array variant

Returns a string with the supplied string or array of strings replaced by a string or an array of strings.

Sintaksė

replace(string, before, after)

Argumentai

  • string - the input string

  • before - the string or array of strings to replace

  • after - the string or array of strings to use as a replacement

Pavyzdžiai

  • replace('QGIS SHOULD ROCK','SHOULD','DOES') → ‚QGIS DOES ROCK‘

  • replace('QGIS ABC',array('A','B','C'),array('X','Y','Z')) → ‚QGIS XYZ‘

  • replace('QGIS',array('Q','S'),'') → ‚GI‘

Map variant

Returns a string with the supplied map keys replaced by paired values. Longer map keys are evaluated first.

Sintaksė

replace(string, map)

Argumentai

  • string - the input string

  • map - the map containing keys and values

Pavyzdžiai

  • replace('APP SHOULD ROCK',map('APP','QGIS','SHOULD','DOES')) → ‚QGIS DOES ROCK‘

  • replace('forty two',map('for','4','two','2','forty two','42')) → ‚42‘

Further reading: regexp_replace, array_replace

9.2.25.17. rpad

Returns a string padded on the right to the specified width, using a fill character. If the target width is smaller than the string’s length, the string is truncated.

Sintaksė

rpad(string, width, fill)

Argumentai

  • string - string to pad

  • width - length of new string

  • fill - character to pad the remaining space with

Pavyzdžiai

  • rpad('Hello', 10, 'x') → ‚Helloxxxxx‘

  • rpad('Hello', 3, 'x') → ‚Hel‘

Further reading: lpad

9.2.25.18. rtrim

Removes the longest string containing only the specified characters (a space by default) from the end of string.

Sintaksė

rtrim(string, [characters=‘ ‚])

[] žymi neprivalomus argumentus

Argumentai

  • string - string to trim

  • characters - characters to trim

Pavyzdžiai

  • rtrim('   hello world  ') → ‚ hello world‘

  • rtrim('testxxzx', 'xyz') → ‚test‘

Further reading: ltrim, trim

9.2.25.19. strpos

Return the first matching position of a substring within another string, or 0 if the substring is not found.

Sintaksė

strpos(haystack, needle)

Argumentai

  • haystack - string that is to be searched

  • needle - string to search for

Pavyzdžiai

  • strpos('HELLO WORLD','WORLD') → 7

  • strpos('HELLO WORLD','GOODBYE') → 0

Further reading: regexp_match

9.2.25.20. substr

Returns a part of a string.

Sintaksė

substr(string, start, [length])

[] žymi neprivalomus argumentus

Argumentai

  • string - the full input string

  • start - integer representing start position to extract beginning with 1; if start is negative, the return string will begin at the end of the string minus the start value

  • length - integer representing length of string to extract; if length is negative, the return string will omit the given length of characters from the end of the string

Pavyzdžiai

  • substr('HELLO WORLD',3,5) → ‚LLO W‘

  • substr('HELLO WORLD',6) → ‚ WORLD‘

  • substr('HELLO WORLD',-5) → ‚WORLD‘

  • substr('HELLO',3,-1) → ‚LL‘

  • substr('HELLO WORLD',-5,2) → ‚WO‘

  • substr('HELLO WORLD',-5,-1) → ‚WORL‘

Further reading: regexp_substr, regexp_matches

9.2.25.21. title

Converts all words of a string to title case (all words lower case with leading capital letter).

Sintaksė

title(string)

Argumentai

  • string - the string to convert to title case

Pavyzdžiai

  • title('hello WOrld') → ‚Hello World‘

Further reading: lower, upper

9.2.25.22. to_string

Converts a number to string.

Sintaksė

to_string(number)

Argumentai

  • number - Integer or real value. The number to convert to string.

Pavyzdžiai

  • to_string(123) → ‚123‘

Further reading: format_number

9.2.25.23. trim

Removes all leading and trailing whitespace (spaces, tabs, etc) from a string.

Sintaksė

trim(string)

Argumentai

  • string - string to trim

Pavyzdžiai

  • trim('   hello world  ') → ‚hello world‘

Further reading: ltrim, rtrim

9.2.25.24. upper

Converts a string to upper case letters.

Sintaksė

upper(string)

Argumentai

  • string - the string to convert to upper case

Pavyzdžiai

  • upper('hello WOrld') → ‚HELLO WORLD‘

Further reading: lower, title

9.2.25.25. wordwrap

Returns a string wrapped to a maximum/minimum number of characters.

Sintaksė

wordwrap(string, wrap_length, [delimiter_string])

[] žymi neprivalomus argumentus

Argumentai

  • string - the string to be wrapped

  • wrap_length - an integer. If wrap_length is positive the number represents the ideal maximum number of characters to wrap; if negative, the number represents the minimum number of characters to wrap.

  • delimiter_string - Optional delimiter string to wrap to a new line.

Pavyzdžiai

  • wordwrap('UNIVERSITY OF QGIS',13) → ‚UNIVERSITY OF<br>QGIS‘

  • wordwrap('UNIVERSITY OF QGIS',-3) → ‚UNIVERSITY<br>OF QGIS‘

9.2.26. User Expressions

This group contains the expressions saved as user expressions.

9.2.27. Variables

This group contains dynamic variables related to the application, the project file and other settings. The availability of variables depends on the context:

  • from the expressionSelect Select by expression dialog

  • from the calculateField Field calculator dialog

  • from the layer properties dialog

  • from the print layout

To use these variables in an expression, they should be preceded by the @ character (e.g, @row_number).

Variable

Aprašymas

algorithm_id

The unique ID of an algorithm

animation_end_time

End of the animation’s overall temporal time range (as a datetime value)

animation_interval

Duration of the animation’s overall temporal time range (as an interval value)

animation_start_time

Start of the animation’s overall temporal time range (as a datetime value)

atlas_feature

The current atlas feature (as feature object)

atlas_featureid

The current atlas feature ID

atlas_featurenumber

The current atlas feature number in the layout

atlas_filename

The current atlas file name

atlas_geometry

The current atlas feature geometry

atlas_layerid

The current atlas coverage layer ID

atlas_layername

The current atlas coverage layer name

atlas_pagename

The current atlas page name

atlas_totalfeatures

The total number of features in atlas

band

The number of the band in the raster layer

band_description

The description of the band in the raster layer

band_name

The name of the band in the raster layer

canvas_cursor_point

The last cursor position on the canvas in the project’s geographical coordinates

cluster_color

The color of symbols within a cluster, or NULL if symbols have mixed colors

cluster_size

The number of symbols contained within a cluster

current_feature

The feature currently being edited in the attribute form or table row

current_geometry

The geometry of the feature currently being edited in the form or the table row

current_parent_feature

represents the feature currently being edited in the parent form. Only usable in an embedded form context.

current_parent_geometry

represents the geometry of the feature currently being edited in the parent form. Only usable in an embedded form context.

form_mode

What the form is used for, like AddFeatureMode, SingleEditMode, MultiEditMode, SearchMode, AggregateSearchMode or IdentifyMode as string.

feature

The current feature being evaluated. This can be used with the ‚attribute‘ function to evaluate attribute values from the current feature.

frame_duration

Temporal duration of each animation frame (as an interval value)

frame_number

Current frame number during animation playback

frame_rate

Number of frames per second during animation playback

fullextent_maxx

Maximum x value from full canvas extent (including all layers)

fullextent_maxy

Maximum y value from full canvas extent (including all layers)

fullextent_minx

Minimum x value from full canvas extent (including all layers)

fullextent_miny

Minimum y value from full canvas extent (including all layers)

geometry

The geometry of the current feature being evaluated

geometry_part_count

The number of parts in rendered feature’s geometry

geometry_part_num

The current geometry part number for feature being rendered

geometry_point_count

The number of points in the rendered geometry’s part

geometry_point_num

The current point number in the rendered geometry’s part

geometry_ring_num

Current geometry ring number for feature being rendered (for polygon features only). The exterior ring has a value of 0.

grid_axis

The current grid annotation axis (eg, ‚x‘ for longitude, ‚y‘ for latitude)

grid_number

The current grid annotation value

id

The ID of the current feature being evaluated

item_id

The layout item user ID (not necessarily unique)

item_uuid

The layout item unique ID

layer

The current layer

layer_crs

The Coordinate Reference System Authority ID of the current layer

layer_crs_ellipsoid

The ellipsoid Authority ID of the current layer CRS

layer_cursor_point

Point geometry under the mouse position in map canvas (or the GetFeatureInfo position in context of QGIS Server), in active layer’s CRS

layer_id

The ID of current layer

layer_ids

The IDs of all the map layers in the current project as a list

layer_name

The name of current layer

layer_vertical_crs

The Identifier for the vertical coordinate reference system of the layer (e.g., ‚EPSG:5703‘)

layer_vertical_crs_definition

The full definition of the vertical Coordinate reference system of the layer

layer_vertical_crs_description

The name of the vertical Coordinate reference system of the layer

layer_vertical_crs_wkt

The WKT definition of the vertical Coordinate reference system of the current layer

layers

All the map layers in the current project as a list

layout_dpi

The composition resolution (DPI)

layout_name

The layout name

layout_numpages

The number of pages in the layout

layout_page

The page number of the current item in the layout

layout_pageheight

The active page height in the layout (in mm for standard paper sizes, or whatever unit was used for custom paper size)

layout_pageoffsets

Array of Y coordinate of the top of each page. Allows to dynamically position items on pages in a context where page sizes may change

layout_pagewidth

The active page width in the layout (in mm for standard paper sizes, or whatever unit was used for custom paper size)

legend_column_count

The number of columns in the legend

legend_filter_by_map

Indicates if the content of the legend is filtered by the map

legend_filter_out_atlas

Indicates if the atlas is filtered out of the legend

legend_split_layers

Indicates if layers can be split in the legend

legend_title

The title of the legend

legend_wrap_string

The character(s) used to wrap the legend text

map_crs

The Coordinate reference system of the current map

map_crs_acronym

The acronym of the Coordinate reference system of the current map

map_crs_definition

The full definition of the Coordinate reference system of the current map

map_crs_description

The name of the Coordinate reference system of the current map

map_crs_ellipsoid

The acronym of the ellipsoid of the Coordinate reference system of the current map

map_crs_proj4

The Proj4 definition of the Coordinate reference system of the current map

map_crs_projection

The descriptive name of the projection method used by the Coordinate reference system of the map (e.g. ‚Albers Equal Area‘)

map_crs_wkt

The WKT definition of the Coordinate reference system of the current map

map_end_time

The end of the map’s temporal time range (as a datetime value)

map_extent

The geometry representing the current extent of the map

map_extent_center

The point feature at the center of the map

map_extent_height

The current height of the map

map_extent_width

The current width of the map

map_id

The ID of current map destination. This will be ‚canvas‘ for canvas renders, and the item ID for layout map renders

map_interval

The duration of the map’s temporal time range (as an interval value)

map_layer_ids

The list of map layer IDs visible in the map

map_layers

The list of map layers visible in the map

map_rotation

The current rotation of the map

map_scale

The current scale of the map

map_start_time

The start of the map’s temporal time range (as a datetime value)

map_units

The units of map measurements

map_z_range_lower

Lower elevation of the map’s elevation range

map_z_range_upper

Upper elevation of the map’s elevation range

model_path

Full path (including file name) of current model (or project path if model is embedded in a project).

model_folder

Folder containing current model (or project folder if model is embedded in a project).

model_name

Name of current model

model_group

Group for current model

notification_message

Content of the notification message sent by the provider (available only for actions triggered by provider notifications).

parent

Refers to the current feature in the parent layer, providing access to its attributes and geometry when filtering an aggregate function

plot_axis

The associated plot axis, e.g. ‚x‘ or ‚y‘.

plot_axis_value

The current value for the plot axis.

project_abstract

The project abstract, taken from project metadata

project_area_units

The area unit for the current project, used when calculating areas of geometries

project_author

The project author, taken from project metadata

project_basename

The basename of current project’s filename (without path and extension)

project_creation_date

The project creation date, taken from project metadata

project_crs

Identifier for the coordinate reference system of the project (e.g., ‚EPSG:4326‘)

project_crs_arconym

The acronym of the Coordinate reference system of the project

project_crs_definition

The full definition of the Coordinate reference system of the project

project_crs_description

The description of the Coordinate reference system of the project

project_crs_ellipsoid

The ellipsoid of the Coordinate reference system of the project

project_crs_proj4

The Proj4 representation of the Coordinate reference system of the project

project_crs_wkt

The WKT (well known text) representation of the coordinate reference system of the project

project_distance_units

The distance unit for the current project, used when calculating lengths of geometries and distances

project_ellipsoid

The name of the ellipsoid of the current project, used when calculating geodetic areas or lengths of geometries

project_filename

The filename of the current project

project_folder

The folder of the current project

project_home

The home path of the current project

project_identifier

The project identifier, taken from the project’s metadata

project_keywords

The project keywords, taken from the project’s metadata

project_last_saved

Date/time when project was last saved.

project_path

The full path (including file name) of the current project

project_title

The title of current project

project_units

The units of the project’s CRS

project_vertical_crs

Identifier for the vertical Coordinate reference system of the project (e.g., ‚EPSG:5703‘)

project_vertical_crs_definition

The full definition of the vertical coordinate reference system of the project

project_vertical_crs_description

The description of the vertical coordinate reference system of the project

project_vertical_crs_wkt

The WKT (well known text) representation of the vertical coordinate reference system of the project

qgis_locale

The current language of QGIS

qgis_os_name

The current Operating system name, eg ‚windows‘, ‚linux‘ or ‚osx‘

qgis_platform

The QGIS platform, eg ‚desktop‘ or ‚server‘

qgis_release_name

The current QGIS release name

qgis_short_version

The current QGIS version short string

qgis_version

The current QGIS version string

qgis_version_no

The current QGIS version number

row_number

Stores the number of the current row

snapping_results

Gives access to snapping results while digitizing a feature (only available in add feature)

scale_value

The current scale bar distance value

selected_file_path

Selected file path from file widget selector when uploading a file with an external storage system

symbol_angle

The angle of the symbol used to render the feature (valid for marker symbols only)

symbol_color

The color of the symbol used to render the feature

symbol_count

The number of features represented by the symbol (in the layout legend)

symbol_frame

The frame number (for animated symbols only)

symbol_id

The Internal ID of the symbol (in the layout legend)

symbol_label

The label for the symbol (either a user defined label or the default autogenerated label - in the layout legend)

symbol_layer_count

Total number of symbol layers in the symbol

symbol_layer_index

Current symbol layer index

symbol_marker_column

Column number for marker (valid for point pattern fills only).

symbol_marker_row

Row number for marker (valid for point pattern fills only).

user_account_name

The current user’s operating system account name

user_full_name

The current user’s operating system user name

value

The current value

vector_tile_zoom

Exact vector tile zoom level of the map that is being rendered (derived from the current map scale). Normally in interval [0, 20]. Unlike @zoom_level, this variable is a floating point value which can be used to interpolate values between two integer zoom levels.

with_variable

Allows setting a variable for usage within an expression and avoid recalculating the same value repeatedly

zoom_level

Vector tile zoom level of the map that is being rendered (derived from the current map scale). Normally in interval [0, 20].

Some examples:

  • Return the X coordinate of a map item center in layout:

    x( map_get( item_variables( 'map1'), 'map_extent_center' ) )
    
  • Return, for each feature in the current layer, the number of overlapping airport features:

    aggregate( layer:='airport', aggregate:='count', expression:="code",
                   filter:=intersects( $geometry, geometry( @parent ) ) )
    
  • Get the object_id of the first snapped point of a line:

    with_variable(
      'first_snapped_point',
      array_first( @snapping_results ),
      attribute(
        get_feature_by_id(
          map_get( @first_snapped_point, 'layer' ),
          map_get( @first_snapped_point, 'feature_id' )
        ),
        'object_id'
      )
    )
    

9.2.28. Recent Functions

This group contains recently used functions. Depending on the context of its usage (feature selection, field calculator, generic), recently applied expressions are added to the corresponding list (up to ten expressions), sorted from more to less recent. This makes it easy to quickly retrieve and reapply previously used expressions.