Raster analysis

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 The batch processing interface or from the QGIS Python console 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.

Parameters

Label Name 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)

Optional

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)

Optional

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 [extent] 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

Optional

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.
Output OUTPUT

[raster]

Default: [Save to temporary file]

Specification of the output raster. One of:

  • Save to a Temporary File
  • Save to File…

The file encoding can also be changed here.

Outputs

Label Name Type Description
Output 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.

Parameters

Label Name Type Description
Input layer INPUT [raster] Input raster layer
Band number 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.
Output OUTPUT_HTML_FILE

[html]

Default: [Save to temporary file]

Specification of the output file:

  • Skip Output
  • Save to a Temporary File
  • Save to File…

The file encoding can also be changed here.

Outputs

Label Name Type Description
Maximum value MAX [number]  
Mean value MEAN [number]  
Minimum value MIN [number]  
Output 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
Range RANGE [number]  
Standard deviation STD_DEV [number]  
Sum 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.

Parameters

Label Name Type Description
Input layer INPUT [raster] Input raster layer
Band number 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:

  • Skip Output
  • Save to a Temporary File
  • Save to File…

The file encoding can also be changed here.

Unique values table OUTPUT_TABLE

[table]

Default: [Skip output]

Specification of the table for unique values:

  • Skip Output
  • Create Temporary Layer
  • Save to File…
  • Save to GeoPackage…
  • Save to PostGIS Table…

The file encoding can also be changed here.

Outputs

Label Name Type Description
CRS authority identifier CRS_AUTHID [crs]  
Extent EXTENT [extent]  
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.

Parameters

Label Name Type Description
Raster layer INPUT_RASTER [raster] Raster layer to reclassify
Band number 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]

Default: 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]

Default: False

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

[enumeration]

Default: 5

Defines the data type of the output raster file. 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]

Specification of the output raster. One of:

  • Save to a Temporary File
  • Save to File…

The file encoding can also be changed here.

Outputs

Label Name 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.

Parameters

Label Name Type Description
Raster layer INPUT_RASTER [raster] Raster layer to reclassify
Band number 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]

Default: 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]

Default: False

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

[enumeration]

Default: 5

Defines the data type of the output raster file. 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]

Specification of the output raster. One of:

  • Save to a Temporary File
  • Save to File…

The file encoding can also be changed here.

Outputs

Label Name 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.

Parameters

Label Name 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)
  • Save to File…
  • Save to Geopackage…
  • Save to PostGIS Table

The file encoding can also be changed here.

Outputs

Label Name 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

Parameters

Label Name Type Description
Raster layer INPUT_RASTER [raster] Input raster layer
Band number 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

Optional

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)
  • Save to File…
  • Save to Geopackage…
  • Save to PostGIS Table

The file encoding can also be changed here.

Outputs

Label Name 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.

Warning

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

Parameters

Label Name Type Description
Raster Layer INPUT_RASTER [raster] Input raster layer
Band number 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

Optional

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

Outputs

Label Name Type Description
Vector layer containing the zones INPUT_VECTOR [vector: polygon] The input polygon vector layer with new fields added for the zone statistics.