QgsZonalStatistics Class Reference

A class that calculates raster statistics (count, sum, mean) for a polygon or multipolygon layer and appends the results as attributes. More...

#include <qgszonalstatistics.h>

Public Types
enum	Result {   Success = 0 , LayerTypeWrong = 1 , LayerInvalid , RasterInvalid ,   RasterBandInvalid , FailedToCreateField = 8 , Canceled = 9 }
	Error codes for calculation. More...
enum	Statistic {   Count = 1 , Sum = 2 , Mean = 4 , Median = 8 ,   StDev = 16 , Min = 32 , Max = 64 , Range = 128 ,   Minority = 256 , Majority = 512 , Variety = 1024 , Variance = 2048 ,   All = Count | Sum | Mean | Median | StDev | Max | Min | Range | Minority | Majority | Variety | Variance }
	Enumeration of flags that specify statistics to be calculated. More...

Public Member Functions
	QgsZonalStatistics (QgsVectorLayer *polygonLayer, QgsRasterInterface *rasterInterface, const QgsCoordinateReferenceSystem &rasterCrs, double rasterUnitsPerPixelX, double rasterUnitsPerPixelY, const QString &attributePrefix=QString(), int rasterBand=1, QgsZonalStatistics::Statistics stats=QgsZonalStatistics::Statistics(QgsZonalStatistics::Count|QgsZonalStatistics::Sum|QgsZonalStatistics::Mean))
	Constructor for QgsZonalStatistics, using a QgsRasterInterface.
	QgsZonalStatistics (QgsVectorLayer *polygonLayer, QgsRasterLayer *rasterLayer, const QString &attributePrefix=QString(), int rasterBand=1, QgsZonalStatistics::Statistics stats=QgsZonalStatistics::Statistics(QgsZonalStatistics::Count|QgsZonalStatistics::Sum|QgsZonalStatistics::Mean))
	Convenience constructor for QgsZonalStatistics, using an input raster layer.
QgsZonalStatistics::Result	calculateStatistics (QgsFeedback *feedback)
	Runs the calculation.

Static Public Member Functions
static QMap< QgsZonalStatistics::Statistic, QVariant >	calculateStatistics (QgsRasterInterface *rasterInterface, const QgsGeometry &geometry, double cellSizeX, double cellSizeY, int rasterBand, QgsZonalStatistics::Statistics statistics)
	Calculates the specified statistics for the pixels of rasterBand in rasterInterface (a raster layer dataProvider() ) within polygon geometry.
static QString	displayName (QgsZonalStatistics::Statistic statistic)
	Returns the friendly display name for a statistic.
static QString	shortName (QgsZonalStatistics::Statistic statistic)
	Returns a short, friendly display name for a statistic, suitable for use in a field name.

Detailed Description

A class that calculates raster statistics (count, sum, mean) for a polygon or multipolygon layer and appends the results as attributes.

Definition at line 46 of file qgszonalstatistics.h.

Member Enumeration Documentation

Result

enum QgsZonalStatistics::Result

Error codes for calculation.

Enumerator
Success	Success.
LayerTypeWrong	Layer is not a polygon layer.
LayerInvalid	Layer is invalid.
RasterInvalid	Raster layer is invalid.
RasterBandInvalid	The raster band does not exist on the raster layer.
FailedToCreateField	Output fields could not be created.
Canceled	Algorithm was canceled.

Definition at line 70 of file qgszonalstatistics.h.

Statistic

enum QgsZonalStatistics::Statistic

Enumeration of flags that specify statistics to be calculated.

Enumerator
Count	Pixel count.
Sum	Sum of pixel values.
Mean	Mean of pixel values.
Median	Median of pixel values.
StDev	Standard deviation of pixel values.
Min	Min of pixel values.
Max	Max of pixel values.
Range	Range of pixel values (max - min)
Minority	Minority of pixel values.
Majority	Majority of pixel values.
Variety	Variety (count of distinct) pixel values.
Variance	Variance of pixel values.
All

Definition at line 51 of file qgszonalstatistics.h.

Constructor & Destructor Documentation

QgsZonalStatistics() [1/2]

QgsZonalStatistics::QgsZonalStatistics	(	QgsVectorLayer *	polygonLayer,
		QgsRasterLayer *	rasterLayer,
		const QString &	attributePrefix = QString(),
		int	rasterBand = 1,
		QgsZonalStatistics::Statistics	stats = QgsZonalStatistics::Statistics( QgsZonalStatistics::Count | QgsZonalStatistics::Sum | QgsZonalStatistics::Mean )
	)

Convenience constructor for QgsZonalStatistics, using an input raster layer.

The raster layer must exist for the lifetime of the zonal statistics calculation.

Warning

Constructing QgsZonalStatistics using this method is not thread safe, and the constructor which accepts a QgsRasterInterface should be used instead.

Definition at line 33 of file qgszonalstatistics.cpp.

QgsZonalStatistics() [2/2]

QgsZonalStatistics::QgsZonalStatistics	(	QgsVectorLayer *	polygonLayer,
		QgsRasterInterface *	rasterInterface,
		const QgsCoordinateReferenceSystem &	rasterCrs,
		double	rasterUnitsPerPixelX,
		double	rasterUnitsPerPixelY,
		const QString &	attributePrefix = QString(),
		int	rasterBand = 1,
		QgsZonalStatistics::Statistics	stats = QgsZonalStatistics::Statistics( QgsZonalStatistics::Count | QgsZonalStatistics::Sum | QgsZonalStatistics::Mean )
	)

Constructor for QgsZonalStatistics, using a QgsRasterInterface.

The polygonLayer gives the vector layer containing the (multi)polygon features corresponding to the different zones. This layer will be modified, adding extra attributes for each of the zonal statistics calculated.

Pixel values for each zone are taken from the raster rasterInterface. The constructor must also be given various properties relating to the input raster, such as the raster CRS (rasterCrs), and the size (X and Y) in map units for each raster pixel. The source raster band is specified via rasterBand, where a value of 1 corresponds to the first band.

If the CRS of the polygonLayer and rasterCrs differ, the calculation will automatically reproject the zones to ensure valid results are calculated.

The attributePrefix argument specifies an optional prefix to use when creating the new fields for each calculated statistic.

Finally, the calculated statistics can be set via the stats argument. A new field will be added to polygonLayer for each statistic calculated.

Warning

The raster interface must exist for the lifetime of the zonal statistics calculation. For thread safe use, always use a cloned raster interface.

Since

QGIS 3.2

Definition at line 45 of file qgszonalstatistics.cpp.

Member Function Documentation

calculateStatistics() [1/2]

QgsZonalStatistics::Result QgsZonalStatistics::calculateStatistics

(

QgsFeedback *

feedback

)

Runs the calculation.

Definition at line 58 of file qgszonalstatistics.cpp.

calculateStatistics() [2/2]

QMap< QgsZonalStatistics::Statistic, QVariant > QgsZonalStatistics::calculateStatistics ( QgsRasterInterface *  rasterInterface, const QgsGeometry &  geometry, double  cellSizeX, double  cellSizeY, int  rasterBand, QgsZonalStatistics::Statistics  statistics  )

static

Calculates the specified statistics for the pixels of rasterBand in rasterInterface (a raster layer dataProvider() ) within polygon geometry.

Returns a map of statistic to result value.

Since

QGIS 3.16

Definition at line 303 of file qgszonalstatistics.cpp.

displayName()

QString QgsZonalStatistics::displayName ( QgsZonalStatistics::Statistic  statistic )

static

Returns the friendly display name for a statistic.

See also

shortName()

Since

QGIS 3.12

Definition at line 222 of file qgszonalstatistics.cpp.

shortName()

QString QgsZonalStatistics::shortName ( QgsZonalStatistics::Statistic  statistic )

static

Returns a short, friendly display name for a statistic, suitable for use in a field name.

See also

displayName()

Since

QGIS 3.12

Definition at line 256 of file qgszonalstatistics.cpp.

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The documentation for this class was generated from the following files:

• /build/qgis-3.34.0+99sid/src/analysis/vector/qgszonalstatistics.h
• /build/qgis-3.34.0+99sid/src/analysis/vector/qgszonalstatistics.cpp