[FEATURE] force_rhr expression function

Forces polygons to follow the right hand rule, in which the area that is bounded by a polygon is to the right of the boundary. In particular, the exterior ring is oriented in a clockwise direction and the interior rings in a counter-clockwise direction.
qgis · Nov 9, 2018 · 1b79b9a · 1b79b9a
1 parent 27e1ef5
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diff --git a/resources/function_help/json/force_rhr b/resources/function_help/json/force_rhr
@@ -0,0 +1,8 @@
+{
+  "name": "force_rhr",
+  "type": "function",
+  "description": "Forces a geometry to respect the Right-Hand-Rule, in which the area that is bounded by a polygon is to the right of the boundary. In particular, the exterior ring is oriented in a clockwise direction and the interior rings in a counter-clockwise direction.",
+  "arguments": [ {"arg":"geom","description":"a geometry. Any non-polygon geometries are returned unchanged."}],
+  "examples": [ { "expression":"geom_to_wkt(force_rhr(geometry:=geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1))')))", "returns":"Polygon ((-1 -1, 0 2, 4 2, 4 0, -1 -1))"}]
+}
+
diff --git a/src/core/expression/qgsexpressionfunction.cpp b/src/core/expression/qgsexpressionfunction.cpp
@@ -2692,6 +2692,46 @@ static QVariant fcnBuffer( const QVariantList &values, const QgsExpressionContex
   return result;
 }
 
+static QVariant fcnForceRHR( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent, const QgsExpressionNodeFunction * )
+{
+  QgsGeometry fGeom = QgsExpressionUtils::getGeometry( values.at( 0 ), parent );
+  if ( fGeom.isMultipart() )
+  {
+    const QgsGeometryCollection *collection = qgsgeometry_cast< const QgsGeometryCollection * >( fGeom.constGet() );
+    std::unique_ptr< QgsGeometryCollection > newCollection( collection->createEmptyWithSameType() );
+    for ( int i = 0; i < collection->numGeometries(); ++i )
+    {
+      const QgsAbstractGeometry *g = collection->geometryN( i );
+      if ( const QgsCurvePolygon *cp = qgsgeometry_cast< const QgsCurvePolygon * >( g ) )
+      {
+        std::unique_ptr< QgsCurvePolygon > corrected( cp->clone() );
+        corrected->forceRHR();
+        newCollection->addGeometry( corrected.release() );
+      }
+      else
+      {
+        newCollection->addGeometry( g->clone() );
+      }
+    }
+    QgsGeometry geom( std::move( newCollection ) );
+    return !geom.isNull() ? QVariant::fromValue( geom ) : QVariant();
+  }
+  else
+  {
+    if ( const QgsCurvePolygon *cp = qgsgeometry_cast< const QgsCurvePolygon * >( fGeom.constGet() ) )
+    {
+      std::unique_ptr< QgsCurvePolygon > corrected( cp->clone() );
+      corrected->forceRHR();
+      QgsGeometry geom( std::move( corrected ) );
+      return !geom.isNull() ? QVariant::fromValue( geom ) : QVariant();
+    }
+    else
+    {
+      return fGeom;
+    }
+  }
+}
+
 static QVariant fcnWedgeBuffer( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent, const QgsExpressionNodeFunction * )
 {
   QgsGeometry fGeom = QgsExpressionUtils::getGeometry( values.at( 0 ), parent );
@@ -4687,6 +4727,8 @@ const QList<QgsExpressionFunction *> &QgsExpression::Functions()
         << new QgsStaticExpressionFunction( QStringLiteral( "within" ), 2, fcnWithin, QStringLiteral( "GeometryGroup" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "translate" ), 3, fcnTranslate, QStringLiteral( "GeometryGroup" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "buffer" ), -1, fcnBuffer, QStringLiteral( "GeometryGroup" ) )
+        << new QgsStaticExpressionFunction( QStringLiteral( "force_rhr" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "geometry" ) ),
+                                            fcnForceRHR, QStringLiteral( "GeometryGroup" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "wedge_buffer" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "center" ) )
                                             << QgsExpressionFunction::Parameter( QStringLiteral( "azimuth" ) )
                                             << QgsExpressionFunction::Parameter( QStringLiteral( "width" ) )

diff --git a/tests/src/core/testqgsexpression.cpp b/tests/src/core/testqgsexpression.cpp
@@ -816,6 +816,12 @@ class TestQgsExpression: public QObject
       QTest::newRow( "geometry_n collection" ) << "geom_to_wkt(geometry_n(geom_from_wkt('GEOMETRYCOLLECTION(POINT(0 1), POINT(0 0), POINT(1 0), POINT(1 1))'),3))" << false << QVariant( QStringLiteral( "Point (1 0)" ) );
       QTest::newRow( "geometry_n collection bad index 1" ) << "geometry_n(geom_from_wkt('GEOMETRYCOLLECTION(POINT(0 1), POINT(0 0), POINT(1 0), POINT(1 1))'),0)" << false << QVariant();
       QTest::newRow( "geometry_n collection bad index 2" ) << "geometry_n(geom_from_wkt('GEOMETRYCOLLECTION(POINT(0 1), POINT(0 0), POINT(1 0), POINT(1 1))'),5)" << false << QVariant();
+      QTest::newRow( "force_rhr not geom" ) << "force_rhr('g')" << true << QVariant();
+      QTest::newRow( "force_rhr null" ) << "force_rhr(NULL)" << false << QVariant();
+      QTest::newRow( "force_rhr point" ) << "geom_to_wkt(force_rhr(geom_from_wkt('POINT(1 2)')))" << false << QVariant( "Point (1 2)" );
+      QTest::newRow( "force_rhr polygon" ) << "geom_to_wkt(force_rhr(geometry:=geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1 -1))')))" << false << QVariant( "Polygon ((-1 -1, 0 2, 4 2, 4 0, -1 -1))" );
+      QTest::newRow( "force_rhr multipolygon" ) << "geom_to_wkt(force_rhr(geometry:=geom_from_wkt('MULTIPOLYGON(Polygon((-1 -1, 4 0, 4 2, 0 2, -1 -1)),Polygon((100 100, 200 100, 200 200, 100 200, 100 100)))')))" << false << QVariant( "MultiPolygon (((-1 -1, 0 2, 4 2, 4 0, -1 -1)),((100 100, 100 200, 200 200, 200 100, 100 100)))" );
+      QTest::newRow( "force_rhr line" ) << "geom_to_wkt(force_rhr(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2)')))" << false << QVariant( "LineString (0 0, 1 1, 2 2)" );
       QTest::newRow( "boundary not geom" ) << "boundary('g')" << true << QVariant();
       QTest::newRow( "boundary null" ) << "boundary(NULL)" << false << QVariant();
       QTest::newRow( "boundary point" ) << "boundary(geom_from_wkt('POINT(1 2)'))" << false << QVariant();

diff --git a/tests/testdata/zip/landsat_b1.tif.gz.properties b/tests/testdata/zip/landsat_b1.tif.gz.properties
@@ -0,0 +1,2 @@
+compressed_size=12008
+uncompressed_size=40684