If no geomCalculator is set for QgsExpression, perform cartesian

calculations for $length, $area, $perimeter (refs #13209)

ie, the default is now to use planimeteric calculations unless
a geomCalculator has been explicitly set

Author: nyalldawson

python/core/qgsexpression.sip

@@ -136,12 +136,18 @@ class QgsExpression
     //! expression() instead.
     QString dump() const;
 
-    //! Return calculator used for distance and area calculations
-    //! (used by internal functions)
+    /** Return calculator used for distance and area calculations
+     * (used by $length, $area and $perimeter functions only)
+     * @see setGeomCalculator()
+     */
     QgsDistanceArea *geomCalculator();
 
-    //! Sets the geometry calculator used in evaluation of expressions,
-    // instead of the default.
+    /** Sets the geometry calculator used for distance and area calculations in expressions.
+     * (used by $length, $area and $perimeter functions only). By default, no geometry
+     * calculator is set and all distance and area calculations are performed using simple
+     * cartesian methods (ie no ellipsoidal calculations).
+     * @see geomCalculator()
+     */
     void setGeomCalculator( const QgsDistanceArea &calc );
 
     /** This function currently replaces each expression between [% and %]

src/core/qgsexpression.cpp

@@ -1658,7 +1658,14 @@ static QVariant fcnGeomArea( const QVariantList&, const QgsExpressionContext* co
   FEAT_FROM_CONTEXT( context, f );
   ENSURE_GEOM_TYPE( f, g, QGis::Polygon );
   QgsDistanceArea* calc = parent->geomCalculator();
-  return QVariant( calc->measureArea( f.constGeometry() ) );
+  if ( calc )
+  {
+    return QVariant( calc->measureArea( f.constGeometry() ) );
+  }
+  else
+  {
+    return QVariant( f.constGeometry()->area() );
+  }
 }
 
 static QVariant fcnArea( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
@@ -1676,15 +1683,29 @@ static QVariant fcnGeomLength( const QVariantList&, const QgsExpressionContext*
   FEAT_FROM_CONTEXT( context, f );
   ENSURE_GEOM_TYPE( f, g, QGis::Line );
   QgsDistanceArea* calc = parent->geomCalculator();
-  return QVariant( calc->measureLength( f.constGeometry() ) );
+  if ( calc )
+  {
+    return QVariant( calc->measureLength( f.constGeometry() ) );
+  }
+  else
+  {
+    return QVariant( f.constGeometry()->length() );
+  }
 }
 
 static QVariant fcnGeomPerimeter( const QVariantList&, const QgsExpressionContext* context, QgsExpression* parent )
 {
   FEAT_FROM_CONTEXT( context, f );
   ENSURE_GEOM_TYPE( f, g, QGis::Polygon );
   QgsDistanceArea* calc = parent->geomCalculator();
-  return QVariant( calc->measurePerimeter( f.constGeometry() ) );
+  if ( calc )
+  {
+    return QVariant( calc->measurePerimeter( f.constGeometry() ) );
+  }
+  else
+  {
+    return f.constGeometry()->isEmpty() ? QVariant( 0 ) : QVariant( f.constGeometry()->geometry()->perimeter() );
+  }
 }
 
 static QVariant fcnPerimeter( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
@@ -3387,7 +3408,6 @@ QString QgsExpression::dump() const
 
 QgsDistanceArea* QgsExpression::geomCalculator()
 {
-  initGeomCalculator();
   return d->mCalc.data();
 }
 

src/core/qgsexpression.h

@@ -275,12 +275,19 @@ class CORE_EXPORT QgsExpression
     //! expression() instead.
     QString dump() const;
 
-    //! Return calculator used for distance and area calculations
-    //! (used by internal functions)
+    /** Return calculator used for distance and area calculations
+     * (used by $length, $area and $perimeter functions only)
+     * @see setGeomCalculator()
+     */
     QgsDistanceArea* geomCalculator();
 
-    //! Sets the geometry calculator used in evaluation of expressions,
-    //! instead of the default.
+    /** Sets the geometry calculator used for distance and area calculations in expressions.
+     * (used by $length, $area and $perimeter functions only). By default, no geometry
+     * calculator is set and all distance and area calculations are performed using simple
+     * cartesian methods (ie no ellipsoidal calculations).
+     * @see geomCalculator()
+     */
+    //TODO QGIS 3.0 change calc to a pointer, so that calculator can be cleared by passing nullptr
     void setGeomCalculator( const QgsDistanceArea &calc );
 
     /** This function currently replaces each expression between [% and %]

tests/src/core/testqgsexpression.cpp

@@ -29,6 +29,7 @@
 #include "qgsvectorlayer.h"
 #include "qgsmaplayerregistry.h"
 #include "qgsvectordataprovider.h"
+#include "qgsdistancearea.h"
 
 static void _parseAndEvalExpr( int arg )
 {
@@ -1296,6 +1297,59 @@ class TestQgsExpression: public QObject
 
     }
 
+    void geom_calculator()
+    {
+      //test calculations with and without geometry calculator set
+      QgsDistanceArea da;
+      da.setSourceAuthId( "EPSG:3111" );
+      da.setEllipsoid( "WGS84" );
+      da.setEllipsoidalMode( true );
+
+      QgsFeature feat;
+      QgsPolyline polygonRing3111;
+      polygonRing3111 << QgsPoint( 2484588, 2425722 ) << QgsPoint( 2482767, 2398853 ) << QgsPoint( 2520109, 2397715 ) << QgsPoint( 2520792, 2425494 ) << QgsPoint( 2484588, 2425722 );
+      QgsPolygon polygon3111;
+      polygon3111 << polygonRing3111;
+      feat.setGeometry( QgsGeometry::fromPolygon( polygon3111 ) );
+      QgsExpressionContext context;
+      context.setFeature( feat );
+
+      // test area without geomCalculator
+      QgsExpression expArea( "$area" );
+      QVariant vArea = expArea.evaluate( &context );
+      QCOMPARE( vArea.toDouble(), 1005640568.0 );
+
+      // test area with geomCalculator
+      expArea.setGeomCalculator( da );
+      vArea = expArea.evaluate( &context );
+      QVERIFY( qgsDoubleNear( vArea.toDouble(), 1009089816.617, 0.001 ) );
+
+      // test perimeter without geomCalculator
+      QgsExpression expPerimeter( "$perimeter" );
+      QVariant vPerimeter = expPerimeter.evaluate( &context );
+      QVERIFY( qgsDoubleNear( vPerimeter.toDouble(), 128282.086, 0.001 ) );
+
+      // test perimeter with geomCalculator
+      expPerimeter.setGeomCalculator( da );
+      vPerimeter = expPerimeter.evaluate( &context );
+      QVERIFY( qgsDoubleNear( vPerimeter.toDouble(), 128289.074, 0.001 ) );
+
+      // test length without geomCalculator
+      QgsPolyline line3111;
+      line3111 << QgsPoint( 2484588, 2425722 ) << QgsPoint( 2482767, 2398853 );
+      feat.setGeometry( QgsGeometry::fromPolyline( line3111 ) );
+      context.setFeature( feat );
+
+      QgsExpression expLength( "$length" );
+      QVariant vLength = expLength.evaluate( &context );
+      QVERIFY( qgsDoubleNear( vLength.toDouble(), 26930.637, 0.001 ) );
+
+      // test length with geomCalculator
+      expLength.setGeomCalculator( da );
+      vLength = expLength.evaluate( &context );
+      QVERIFY( qgsDoubleNear( vLength.toDouble(), 26932.156, 0.001 ) );
+    }
+
     void eval_geometry_wkt()
     {
       QgsPolyline polyline, polygon_ring;