Analyse raster

Raster calculator

Performs algebraic operations using raster layers.

The resulting layer will have its values computed according to an expression. The expression can contain numerical values, operators and references to any of the layers in the current project.

Note

When using the calculator in L’interface de traitement par lot or from the La Console Python de QGIS the files to use have to be specified. The corresponding layers are referred using the base name of the file (without the full path). For instance, if using a layer at path/to/my/rasterfile.tif, the first band of that layer will be referred as rasterfile.tif@1.

Paramètres

Étiquette

Nom

Type

Description

Layers

GUI only

Shows the list of all raster layers loaded in the legend. These can be used to fill the expression box (double click to add). Raster layers are referred by their name and the number of the band: layer_name@band_number. For instance, the first band from a layer named DEM will be referred as DEM@1.

Operators

GUI only

Contains some calculator like buttons that can be used to fill the expression box.

Expression

EXPRESSION

[string]

Expression that will be used to calculate the output raster layer. You can use the operator buttons provided to type directly the expression in this box.

Predefined expressions

GUI only

You can use the predefined NDVI expression or you can define new expressions for calculations. The Add… button loads a defined expression (and lets you set the parameters). The Save… button lets you define a new expression.

Reference layer(s) (used for automated extent, cellsize, and CRS)

Optionnel

LAYERS

[raster] [list]

Layer(s) that will be used to fetch extent, cell size and CRS. By choosing the layer in this box you avoid filling in all the other parameters by hand. Raster layers are referred by their name and the number of the band: layer_name@band_number. For instance, the first band from a layer named DEM will be referred as DEM@1.

Cell size (use 0 or empty to set it automatically)

Optionnel

CELLSIZE

[number]

Cell size of the output raster layer. If the cell size is not specified, the minimum cell size of the selected reference layer(s) will be used. The cell size will be the same for the X and Y axes.

Output extent (xmin, xmax, ymin, ymax)

EXTENT

[emprise]

Extent of the output raster layer. If the extent is not specified, the minimum extent that covers all the selected reference layers will be used.

Output CRS

Optionnel

CRS

[crs]

CRS of the output raster layer. If the output CRS is not specified, the CRS of the first reference layer will be used.

Rendu

OUTPUT

[raster]

Default: [Save to temporary file]

Spécification pour le raster en sortie. Au choix :

  • Enregistrer dans un fichier temporaire

  • Enregistrer dans un fichier…

L’encodage du fichier peut également être modifié ici.

Sorties

Étiquette

Nom

Type

Description

Rendu

OUTPUT

[raster]

Output raster file with the calculated values.

Raster layer statistics

Calculates basic statistics from the values in a given band of the raster layer. The output is loaded in the Processing ‣ Results viewer menu.

Paramètres

Étiquette

Nom

Type

Description

Couche en entrée

INPUT

[raster]

Couche raster source

Numéro de bande

BAND

[raster band]

Default: The first band of the input layer

If the raster is multiband, choose the band you want to get statistics for.

Rendu

OUTPUT_HTML_FILE

[html]

Default: [Save to temporary file]

Specification of the output file:

  • Ignorer la sortie

  • Enregistrer dans un fichier temporaire

  • Enregistrer dans un fichier…

L’encodage du fichier peut également être modifié ici.

Sorties

Étiquette

Nom

Type

Description

Valeur maximale

MAX

[number]

Valeur moyenne

MEAN

[number]

Valeur minimum

MIN

[number]

Rendu

OUTPUT_HTML_FILE

[html]

The output file contains the following information:

  • Analyzed file: path of the raster layer

  • Minimum value: minimum value of the raster

  • Maximum value: maximum value of the raster

  • Range: difference between the maximum and minimum values

  • Sum: total sum of the values

  • Mean value: mean of the values

  • Standard deviation: standard deviation of the values

  • Sum of the squares: sum of the squared differences of each observation from the overall mean

Gamme

RANGE

[number]

Écart-type

STD_DEV

[number]

Somme

SUM

[number]

Sum of the squares

SUM_OF_SQUARES

[number]

Raster layer unique values report

Returns the count and area of each unique value in a given raster layer.

Paramètres

Étiquette

Nom

Type

Description

Couche en entrée

INPUT

[raster]

Couche raster source

Numéro de bande

BAND

[raster band]

Default: The first band of the input layer

If the raster is multiband, choose the band you want to get statistics for.

Unique values report

OUTPUT_HTML_FILE

[file]

Default: [Save to temporary file]

Specification of the output file:

  • Ignorer la sortie

  • Enregistrer dans un fichier temporaire

  • Enregistrer dans un fichier…

L’encodage du fichier peut également être modifié ici.

Unique values table

OUTPUT_TABLE

[table]

Par défaut: [Skip output]

Specification of the table for unique values:

  • Ignorer la sortie

  • Créer une couche temporaire

  • Enregistrer dans un fichier…

  • Save to GeoPackage…

  • Enregistrer dans la table PostGIS …

L’encodage du fichier peut également être modifié ici.

Sorties

Étiquette

Nom

Type

Description

CRS authority identifier

CRS_AUTHID

[crs]

Extent

EXTENT

[emprise]

Height in pixels

HEIGHT_IN_PIXELS

[number]

NODATA pixel count

NODATA_PIXEL_COUNT

[number]

Total pixel count

TOTAL_PIXEL_COUNT

[number]

Unique values report

OUTPUT_HTML_FILE

[html]

The output HTML file contains the following information:

  • Analyzed file: the path of the raster layer

  • Extent: xmin, ymin, xmax, ymax coordinates of the extent

  • Projection: projection of the layer

  • Width in pixels: number of columns and pixel width size

  • Height in pixels: number of rows and pixel width size

  • Total pixel count: count of all the pixels

  • NODATA pixel count: count of pixels with NODATA value

Unique values table

OUTPUT_TABLE

[table]

A table with three columns:

  • value: pixel value

  • count: count of pixels with this value

  • m2: total area in square meters of pixels with this value.

Width in pixels

WIDTH_IN_PIXELS

[number]

Reclassify by layer

Reclassifies a raster band by assigning new class values based on the ranges specified in a vector table.

Paramètres

Étiquette

Nom

Type

Description

Couche raster

INPUT_RASTER

[raster]

Raster layer to reclassify

Numéro de bande

RASTER_BAND

[raster band]

Default: The first band of the raster layer

If the raster is multiband, choose the band you want to reclassify.

Layer containing class breaks

INPUT_TABLE

[vector: any]

Vector layer containing the values to use for classification.

Minimum class value field

MIN_FIELD

[tablefield: numeric]

Field with the minimum value of the range for the class.

Maximum class value field

MAX_FIELD

[tablefield: numeric]

Field with the maximum value of the range for the class.

Output value field

VALUE_FIELD

[tablefield: numeric]

Field with the value that will be assigned to the pixels that fall in the class (between the corresponding min and max values).

Output no data value

NO_DATA

[number]

Default: -9999.0

Value to apply to no data values.

Range boundaries

RANGE_BOUNDARIES

[enumeration]

Par défaut : 0

Defines comparison rules for the classification. Options:

  • 0 — min < value <= max

  • 1 — min <= value < max

  • 2 — min <= value <= max

  • 3 — min < value < max

Use no data when no range matches value

NODATA_FOR_MISSING

[boolean]

Par défaut : Faux

Values that do not belong to a class will result in the no data value. If False, the original value is kept.

Type de données de sortie

DATA_TYPE

[enumeration]

Par défaut: 5

Définit le type de données du fichier raster en sortie. Options:

  • 0 — Byte

  • 1 — Int16

  • 2 — UInt16

  • 3 — UInt32

  • 4 — Int32

  • 5 — Float32

  • 6 — Float64

  • 7 — CInt16

  • 8 — CInt32

  • 9 — CFloat32

  • 10 — CFloat64

Reclassified raster

OUTPUT

[raster]

Spécification pour le raster en sortie. Au choix :

  • Enregistrer dans un fichier temporaire

  • Enregistrer dans un fichier…

L’encodage du fichier peut également être modifié ici.

Sorties

Étiquette

Nom

Type

Description

Reclassified raster

OUTPUT

[raster]

Output raster layer with reclassified band values

Reclassify by table

Reclassifies a raster band by assigning new class values based on the ranges specified in a fixed table.

Paramètres

Étiquette

Nom

Type

Description

Couche raster

INPUT_RASTER

[raster]

Raster layer to reclassify

Numéro de bande

RASTER_BAND

[raster band]

Default: The first band of the raster layer

If the raster is multiband, choose the band you want to reclassify.

Reclassification table

TABLE

[matrix]

A 3-columns table (formatted as a list of nine numbers) containing the values to use for class boundaries (Minimum and Maximum) and the new Value to assign to the band values that fall in the class.

Output no data value

NO_DATA

[number]

Default: -9999.0

Value to use for nodata in the output

Range boundaries

RANGE_BOUNDARIES

[enumeration]

Par défaut : 0

Defines comparison rules for the classification. Options:

  • 0 — min < value <= max

  • 1 — min <= value < max

  • 2 — min <= value <= max

  • 3 — min < value < max

Use no data when no range matches value

NODATA_FOR_MISSING

[boolean]

Par défaut : Faux

Values that do not belong to a class will result in the no data value. If False, the original value is kept.

Type de données de sortie

DATA_TYPE

[enumeration]

Par défaut: 5

Définit le type de données du fichier raster en sortie. Options:

  • 0 — Byte

  • 1 — Int16

  • 2 — UInt16

  • 3 — UInt32

  • 4 — Int32

  • 5 — Float32

  • 6 — Float64

  • 7 — CInt16

  • 8 — CInt32

  • 9 — CFloat32

  • 10 — CFloat64

Reclassified raster

OUTPUT

[raster]

Spécification pour le raster en sortie. Au choix :

  • Enregistrer dans un fichier temporaire

  • Enregistrer dans un fichier…

L’encodage du fichier peut également être modifié ici.

Sorties

Étiquette

Nom

Type

Description

Reclassified raster

OUTPUT

[raster]

Output raster layer with reclassified band values

Sample raster values

Extracts raster values at the point locations. If the raster layer is multiband, each band is sampled.

The attribute table of the resulting layer will have as many new columns as there are bands in the raster layer.

Paramètres

Étiquette

Nom

Type

Description

Input Point Layer

INPUT

[vector: point]

Point vector layer in input to use for the sampling.

Raster Layer to sample

RASTERCOPY

[raster]

Raster layer to sample at input point layer locations.

Output column prefix

COLUMN_PREFIX

[string]

Default: “rvalue”

Prefix for the column(s) name.

Sampled Points

OUTPUT

[vector: point]

Default: [Create temporary layer]

Specify the output point vector layer for the sampled raster values. One of:

  • Create Temporary Layer (TEMPORARY_OUTPUT)

  • Enregistrer dans un fichier…

  • Enregistrer dans un GeoPackage…

  • Save to PostGIS Table

L’encodage du fichier peut également être modifié ici.

Sorties

Étiquette

Nom

Type

Description

Sampled Points

OUTPUT

[vector: point]

Output point vector layer with additional column(s) containing the sampled raster values.

Zonal histogram

Appends fields representing counts of each unique value from a raster layer contained within zones defined as polygons.

The output layer attribute table will have as many fields as the unique values of the raster layer that intersects the polygon(s).

../../../../_images/raster_histogram.png

Raster layer histogram example

Paramètres

Étiquette

Nom

Type

Description

Couche raster

INPUT_RASTER

[raster]

Couche raster source

Numéro de bande

RASTER_BAND

[raster band]

Default: The first band raster layer to sample

If the raster is multiband, choose the band to use for the zonal histogram.

Vector layer containing the zones

INPUT_VECTOR

[vector: polygon]

Polygon vector layer that defines the zones.

Output column prefix

Optionnel

COLUMN_PREFIX

[string]

Default: “HISTO_”

Prefix for output column name(s).

Output zones

OUTPUT

[vector: polygon]

Default: [Create temporary layer]

Specify the output polygon vector layer with count of raster values. One of:

  • Create Temporary Layer (TEMPORARY_OUTPUT)

  • Enregistrer dans un fichier…

  • Enregistrer dans un GeoPackage…

  • Save to PostGIS Table

L’encodage du fichier peut également être modifié ici.

Sorties

Étiquette

Nom

Type

Description

Output zones

OUTPUT

[vector: polygon]

Output polygon vector layer with count of raster values.

Zonal statistics

Calculates statistics of a raster layer for each feature of an overlapping polygon vector layer.

Avertissement

No new output file will be created. The algorithm adds new columns to the input vector layer.

Paramètres

Étiquette

Nom

Type

Description

Raster Layer

INPUT_RASTER

[raster]

Couche raster source

Numéro de bande

RASTER_BAND

[raster band]

Default: The first band of the raster layer

If the raster is multiband, choose the band to use for the zonal histogram.

Vector layer containing the zones

INPUT_VECTOR

[vector: polygon]

Pologyn vector layer that defines the zones (and that will be updated with new statistics columns).

Output column prefix

Optionnel

COLUMN_PREFIX

[string]

Default: “_”

Prefix for the output column name(s).

Statistics to calculate

STATS

[enumeration] [list]

Default: [0 1 2]

List of statistical operators for the output. The available operators are:

  • 0 – Count

  • 1 – Sum

  • 2 – Mean

  • 3 – Median

  • 4 – St. dev.

  • 5 – Min

  • 6 – Max

  • 7 – Range

  • 8 – Minority

  • 9 – Majority (mode)

  • 10 – Variety

  • 11 – Variance

  • 12 – All

Sorties

Étiquette

Nom

Type

Description

Vector layer containing the zones

INPUT_VECTOR

[vector: polygon]

The input polygon vector layer with new fields added for the zone statistics.