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nyalldawsonnyalldawson
committedNov 22, 2016
[FEATURE] raster_statistic expression function for retrieving
raster band stats from a loaded layer Allows raster band stats (eg min, max, avg) to be used in expressions
·
ltr-3_40final-3_0_0
1 parent 86ab302 commit 20dc7fb

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‎resources/function_help/json/raster_statistic

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{
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"name": "raster_statistic",
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"type": "function",
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"description": "Returns statistics from a raster layer.",
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"arguments": [
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{"arg":"layer", "description":"a string, representing either a raster layer name or layer ID"},
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{"arg":"band", "description":"integer representing the band number from the raster layer, starting at 1"},
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{"arg":"property", "description":"a string corresponding to the property to return. Valid options are:<br /><ul><li>min: minimum value</li><li>max: maximum value</li><li>avg: average (mean) value</li><li>stdev: standard deviation of values</li><li>range: range of values (max - min)</li><li>sum: sum of all values from raster</li></ul>"}
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],
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"examples": [
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{ "expression":"raster_statistic('lc',1,'avg')", "returns":"Average value from band 1 from 'lc' raster layer"},
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{ "expression":"raster_statistic('ac2010',3,'min')", "returns":"Minimum value from band 3 from 'ac2010' raster layer"}
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]
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}

‎src/core/qgsexpression.cpp

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@@ -54,6 +54,8 @@
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#include "qgsmaptopixelgeometrysimplifier.h"
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#include "qgsmessagelog.h"
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#include "qgscsexception.h"
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#include "qgsrasterlayer.h"
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#include "qgsrasterdataprovider.h"
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// from parser
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extern QgsExpression::Node* parseExpression( const QString& str, QString& parserErrorMsg );
@@ -3423,6 +3425,75 @@ static QVariant fcnGetLayerProperty( const QVariantList& values, const QgsExpres
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return QVariant();
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}
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static QVariant fcnGetRasterBandStat( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
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{
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QString layerIdOrName = getStringValue( values.at( 0 ), parent );
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//try to find a matching layer by name
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QgsMapLayer* layer = QgsMapLayerRegistry::instance()->mapLayer( layerIdOrName ); //search by id first
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if ( !layer )
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{
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QList<QgsMapLayer *> layersByName = QgsMapLayerRegistry::instance()->mapLayersByName( layerIdOrName );
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if ( !layersByName.isEmpty() )
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{
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layer = layersByName.at( 0 );
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}
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}
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if ( !layer )
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return QVariant();
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QgsRasterLayer* rl = qobject_cast< QgsRasterLayer* >( layer );
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if ( !rl )
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return QVariant();
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int band = getIntValue( values.at( 1 ), parent );
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if ( band < 1 || band > rl->bandCount() )
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{
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parent->setEvalErrorString( QObject::tr( "Invalid band number %1 for layer %2" ).arg( band ).arg( layerIdOrName ) );
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return QVariant();
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}
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QString layerProperty = getStringValue( values.at( 2 ), parent );
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int stat = 0;
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if ( QString::compare( layerProperty, QStringLiteral( "avg" ), Qt::CaseInsensitive ) == 0 )
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stat = QgsRasterBandStats::Mean;
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else if ( QString::compare( layerProperty, QStringLiteral( "stdev" ), Qt::CaseInsensitive ) == 0 )
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stat = QgsRasterBandStats::StdDev;
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else if ( QString::compare( layerProperty, QStringLiteral( "min" ), Qt::CaseInsensitive ) == 0 )
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stat = QgsRasterBandStats::Min;
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else if ( QString::compare( layerProperty, QStringLiteral( "max" ), Qt::CaseInsensitive ) == 0 )
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stat = QgsRasterBandStats::Max;
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else if ( QString::compare( layerProperty, QStringLiteral( "range" ), Qt::CaseInsensitive ) == 0 )
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stat = QgsRasterBandStats::Range;
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else if ( QString::compare( layerProperty, QStringLiteral( "sum" ), Qt::CaseInsensitive ) == 0 )
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stat = QgsRasterBandStats::Sum;
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else
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{
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parent->setEvalErrorString( QObject::tr( "Invalid raster statistic: '%1'" ).arg( layerProperty ) );
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return QVariant();
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}
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QgsRasterBandStats stats = rl->dataProvider()->bandStatistics( band, stat );
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switch ( stat )
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{
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case QgsRasterBandStats::Mean:
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return stats.mean;
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case QgsRasterBandStats::StdDev:
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return stats.stdDev;
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case QgsRasterBandStats::Min:
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return stats.minimumValue;
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case QgsRasterBandStats::Max:
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return stats.maximumValue;
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case QgsRasterBandStats::Range:
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return stats.range;
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case QgsRasterBandStats::Sum:
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return stats.sum;
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}
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return QVariant();
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}
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static QVariant fcnArray( const QVariantList& values, const QgsExpressionContext*, QgsExpression* )
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{
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return values;
@@ -4007,6 +4078,9 @@ const QList<QgsExpression::Function*>& QgsExpression::Functions()
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// **General** functions
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<< new StaticFunction( QStringLiteral( "layer_property" ), 2, fcnGetLayerProperty, QStringLiteral( "General" ) )
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<< new StaticFunction( QStringLiteral( "raster_statistic" ), ParameterList() << Parameter( QStringLiteral( "layer" ) )
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<< Parameter( QStringLiteral( "band" ) )
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<< Parameter( QStringLiteral( "statistic" ) ), fcnGetRasterBandStat, QStringLiteral( "General" ) )
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<< new StaticFunction( QStringLiteral( "var" ), 1, fcnGetVariable, QStringLiteral( "General" ) )
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//return all attributes string for referencedColumns - this is caught by

‎tests/src/core/testqgsexpression.cpp

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#include "qgsmaplayerregistry.h"
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#include "qgsvectordataprovider.h"
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#include "qgsdistancearea.h"
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#include "qgsrasterlayer.h"
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#include "qgsproject.h"
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static void _parseAndEvalExpr( int arg )
@@ -55,6 +56,7 @@ class TestQgsExpression: public QObject
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, mMemoryLayer( nullptr )
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, mAggregatesLayer( nullptr )
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, mChildLayer( nullptr )
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, mRasterLayer( nullptr )
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{}
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private:
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QgsVectorLayer* mMemoryLayer;
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QgsVectorLayer* mAggregatesLayer;
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QgsVectorLayer* mChildLayer;
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QgsRasterLayer* mRasterLayer;
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private slots:
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@@ -94,6 +97,12 @@ class TestQgsExpression: public QObject
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mPointsLayer->setMaximumScale( 500 );
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mPointsLayer->setMinimumScale( 1000 );
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QString rasterFileName = testDataDir + "tenbytenraster.asc";
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QFileInfo rasterFileInfo( rasterFileName );
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mRasterLayer = new QgsRasterLayer( rasterFileInfo.filePath(),
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rasterFileInfo.completeBaseName() );
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QgsMapLayerRegistry::instance()->addMapLayer( mRasterLayer );
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// test memory layer for get_feature tests
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mMemoryLayer = new QgsVectorLayer( QStringLiteral( "Point?field=col1:integer&field=col2:string" ), QStringLiteral( "test" ), QStringLiteral( "memory" ) );
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QVERIFY( mMemoryLayer->isValid() );
@@ -1039,6 +1048,21 @@ class TestQgsExpression: public QObject
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QTest::newRow( "layer_property storage_type" ) << QStringLiteral( "layer_property('%1','storage_type')" ).arg( mPointsLayer->name() ) << false << QVariant( "ESRI Shapefile" );
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QTest::newRow( "layer_property geometry_type" ) << QStringLiteral( "layer_property('%1','geometry_type')" ).arg( mPointsLayer->name() ) << false << QVariant( "Point" );
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// raster_statistic tests
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QTest::newRow( "raster_statistic no layer" ) << "raster_statistic('',1,'min')" << false << QVariant();
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QTest::newRow( "raster_statistic bad layer" ) << "raster_statistic('bad',1,'min')" << false << QVariant();
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QTest::newRow( "raster_statistic bad band" ) << QStringLiteral( "raster_statistic('%1',0,'min')" ).arg( mRasterLayer->name() ) << true << QVariant();
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QTest::newRow( "raster_statistic bad band 2" ) << QStringLiteral( "raster_statistic('%1',100,'min')" ).arg( mRasterLayer->name() ) << true << QVariant();
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QTest::newRow( "raster_statistic no property" ) << QStringLiteral( "raster_statistic('%1',1,'')" ).arg( mRasterLayer->name() ) << true << QVariant();
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QTest::newRow( "raster_statistic bad property" ) << QStringLiteral( "raster_statistic('%1',1,'bad')" ).arg( mRasterLayer->name() ) << true << QVariant();
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QTest::newRow( "raster_statistic min by id" ) << QStringLiteral( "raster_statistic('%1',1,'min')" ).arg( mRasterLayer->id() ) << false << QVariant( 0.0 );
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QTest::newRow( "raster_statistic min name" ) << QStringLiteral( "raster_statistic('%1',1,'min')" ).arg( mRasterLayer->name() ) << false << QVariant( 0.0 );
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QTest::newRow( "raster_statistic max" ) << QStringLiteral( "raster_statistic('%1',1,'max')" ).arg( mRasterLayer->id() ) << false << QVariant( 9.0 );
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QTest::newRow( "raster_statistic avg" ) << QStringLiteral( "round(10*raster_statistic('%1',1,'avg'))" ).arg( mRasterLayer->id() ) << false << QVariant( 45 );
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QTest::newRow( "raster_statistic stdev" ) << QStringLiteral( "round(100*raster_statistic('%1',1,'stdev'))" ).arg( mRasterLayer->id() ) << false << QVariant( 287 );
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QTest::newRow( "raster_statistic range" ) << QStringLiteral( "raster_statistic('%1',1,'range')" ).arg( mRasterLayer->id() ) << false << QVariant( 9.0 );
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QTest::newRow( "raster_statistic sum" ) << QStringLiteral( "round(raster_statistic('%1',1,'sum'))" ).arg( mRasterLayer->id() ) << false << QVariant( 450 );
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//test conversions to bool
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QTest::newRow( "feature to bool false" ) << QStringLiteral( "case when get_feature('none','none',499) then true else false end" ) << false << QVariant( false );
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QTest::newRow( "feature to bool true" ) << QStringLiteral( "case when get_feature('test','col1',10) then true else false end" ) << false << QVariant( true );

1 commit comments

Comments
 (1)

nirvn commented on Nov 22, 2016

@nirvn
nirvn
on Nov 22, 2016
Contributor

That's a really useful function, thanks. It'd be really cool for it to support an optional 4th parameter that would take a geometry (point, line, or polygon) to limit statistics to pixels overlapping the given geometry.

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