Raster analysis¶

Raster calculator
Raster layer statistics
Raster layer unique values report
Reclassify by layer
Reclassify by table
Sample raster values
Zonal histogram
Zonal statistics

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.

Poznámka

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.

Varování

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.