Add method to QgsGeometryFactory to create a multigeometry

from any wkb type

Eg calling QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::PolygonM )
will return a new QgsMultiPolygonV2 with M values.

Author: nyalldawson

src/core/geometry/qgsgeometryfactory.cpp

@@ -264,3 +264,39 @@ QgsAbstractGeometry *QgsGeometryFactory::geomFromWkbType( QgsWkbTypes::Type t )
       return nullptr;
   }
 }
+
+std::unique_ptr<QgsGeometryCollection> QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::Type t )
+{
+  QgsWkbTypes::Type type = QgsWkbTypes::flatType( QgsWkbTypes::multiType( t ) );
+  std::unique_ptr< QgsGeometryCollection > collect;
+  switch ( type )
+  {
+    case QgsWkbTypes::MultiPoint:
+      collect.reset( new QgsMultiPointV2() );
+      break;
+    case QgsWkbTypes::MultiLineString:
+      collect.reset( new QgsMultiLineString() );
+      break;
+    case QgsWkbTypes::MultiCurve:
+      collect.reset( new QgsMultiCurve() );
+      break;
+    case QgsWkbTypes::MultiPolygon:
+      collect.reset( new QgsMultiPolygonV2() );
+      break;
+    case QgsWkbTypes::MultiSurface:
+      collect.reset( new QgsMultiSurface() );
+      break;
+    case QgsWkbTypes::GeometryCollection:
+      collect.reset( new QgsGeometryCollection() );
+      break;
+    default:
+      // should not be possible
+      return nullptr;
+  }
+  if ( QgsWkbTypes::hasM( t ) )
+    collect->addMValue();
+  if ( QgsWkbTypes::hasZ( t ) )
+    collect->addZValue();
+
+  return collect;
+}

src/core/geometry/qgsgeometryfactory.h

@@ -20,11 +20,13 @@
 
 #include "qgis_core.h"
 #include <QString>
+#include <memory>
 
 class QgsAbstractGeometry;
 class QgsLineString;
 class QgsConstWkbPtr;
 class QgsRectangle;
+class QgsGeometryCollection;
 
 //compatibility with old classes
 #include "qgspointxy.h"
@@ -70,6 +72,12 @@ class CORE_EXPORT QgsGeometryFactory
     //! Return empty geometry from wkb type
     static QgsAbstractGeometry *geomFromWkbType( QgsWkbTypes::Type t );
 
+    /**
+     * Returns a new geometry collection matching a specified WKB \a type. For instance, if
+     * type is PolygonM the returned geometry will be a QgsMultiPolygonV2 with M values.
+     */
+    static std::unique_ptr< QgsGeometryCollection > createCollectionOfType( QgsWkbTypes::Type type );
+
   private:
     static QgsLineString *linestringFromPolyline( const QgsPolyline &polyline );
 };

tests/src/core/testqgsgeometry.cpp

@@ -127,6 +127,7 @@ class TestQgsGeometry : public QObject
     void isSimple();
 
     void reshapeGeometryLineMerge();
+    void createCollectionOfType();
 
   private:
     //! A helper method to do a render check to see if the geometry op is as expected
@@ -5540,5 +5541,38 @@ void TestQgsGeometry::reshapeGeometryLineMerge()
   QCOMPARE( g3D_2.exportToWkt(), QString( "LineStringZ (-10 -10 -1, 10 10 1, 20 20 2)" ) );
 }
 
+void TestQgsGeometry::createCollectionOfType()
+{
+  std::unique_ptr< QgsGeometryCollection > collect( QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::Unknown ) );
+  QVERIFY( !collect );
+  collect = QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::Point );
+  QCOMPARE( collect->wkbType(), QgsWkbTypes::MultiPoint );
+  QVERIFY( dynamic_cast< QgsMultiPointV2 *>( collect.get() ) );
+  collect = QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::PointM );
+  QCOMPARE( collect->wkbType(), QgsWkbTypes::MultiPointM );
+  QVERIFY( dynamic_cast< QgsMultiPointV2 *>( collect.get() ) );
+  collect = QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::PointZM );
+  QCOMPARE( collect->wkbType(), QgsWkbTypes::MultiPointZM );
+  QVERIFY( dynamic_cast< QgsMultiPointV2 *>( collect.get() ) );
+  collect = QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::PointZ );
+  QCOMPARE( collect->wkbType(), QgsWkbTypes::MultiPointZ );
+  QVERIFY( dynamic_cast< QgsMultiPointV2 *>( collect.get() ) );
+  collect = QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::MultiPoint );
+  QCOMPARE( collect->wkbType(), QgsWkbTypes::MultiPoint );
+  QVERIFY( dynamic_cast< QgsMultiPointV2 *>( collect.get() ) );
+  collect = QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::LineStringZ );
+  QCOMPARE( collect->wkbType(), QgsWkbTypes::MultiLineStringZ );
+  QVERIFY( dynamic_cast< QgsMultiLineString *>( collect.get() ) );
+  collect = QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::PolygonM );
+  QCOMPARE( collect->wkbType(), QgsWkbTypes::MultiPolygonM );
+  QVERIFY( dynamic_cast< QgsMultiPolygonV2 *>( collect.get() ) );
+  collect = QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::GeometryCollectionZ );
+  QCOMPARE( collect->wkbType(), QgsWkbTypes::GeometryCollectionZ );
+  QVERIFY( dynamic_cast< QgsGeometryCollection *>( collect.get() ) );
+  collect = QgsGeometryFactory::createCollectionOfType( QgsWkbTypes::CurvePolygonM );
+  QCOMPARE( collect->wkbType(), QgsWkbTypes::MultiSurfaceM );
+  QVERIFY( dynamic_cast< QgsMultiSurface *>( collect.get() ) );
+}
+
 QGSTEST_MAIN( TestQgsGeometry )
 #include "testqgsgeometry.moc"