Add method which promotes all non-point WKB types to multitype

equivalent Specifically, this method should be used to determine the most-permissive possible resultant WKB type which can result from subtracting parts of a geometry. A single-point geometry type can never become a multi-point geometry type as a result of a subtraction, but a single-line or single-polygon geometry CAN become a multipart geometry as a result of subtracting portions of the geometry.
qgis · Dec 9, 2021 · fa12325 · fa12325
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diff --git a/python/core/auto_generated/geometry/qgswkbtypes.sip.in b/python/core/auto_generated/geometry/qgswkbtypes.sip.in
@@ -118,6 +118,8 @@ Returns the single type for a WKB type. For example, for MultiPolygon WKB types
 %Docstring
 Returns the multi type for a WKB type. For example, for Polygon WKB types the multi type would be MultiPolygon.
 
+.. seealso:: :py:func:`promoteNonPointTypesToMulti`
+
 .. seealso:: :py:func:`isMultiType`
 
 .. seealso:: :py:func:`singleType`
@@ -128,6 +130,22 @@ Returns the multi type for a WKB type. For example, for Polygon WKB types the mu
 %End
 
 
+    static Type promoteNonPointTypesToMulti( Type type ) /HoldGIL/;
+%Docstring
+Promotes a WKB geometry type to its multi-type equivalent, with the exception of point geometry types.
+
+Specifically, this method should be used to determine the most-permissive possible resultant WKB type which can result
+from subtracting parts of a geometry. A single-point geometry type can never become a multi-point geometry type as
+a result of a subtraction, but a single-line or single-polygon geometry CAN become a multipart geometry as a result of subtracting
+portions of the geometry.
+
+.. seealso:: :py:func:`multiType`
+
+.. seealso:: :py:func:`singleType`
+
+.. versionadded:: 3.24
+%End
+
     static Type curveType( Type type ) /HoldGIL/;
 %Docstring
 Returns the curve type for a WKB type. For example, for Polygon WKB types the curve type would be CurvePolygon.

diff --git a/src/core/geometry/qgswkbtypes.h b/src/core/geometry/qgswkbtypes.h
@@ -294,6 +294,8 @@ class CORE_EXPORT QgsWkbTypes
 
     /**
      * Returns the multi type for a WKB type. For example, for Polygon WKB types the multi type would be MultiPolygon.
+     *
+     * \see promoteNonPointTypesToMulti()
      * \see isMultiType()
      * \see singleType()
      * \see curveType()
@@ -434,6 +436,34 @@ class CORE_EXPORT QgsWkbTypes
     }
 
 
+    /**
+     * Promotes a WKB geometry type to its multi-type equivalent, with the exception of point geometry types.
+     *
+     * Specifically, this method should be used to determine the most-permissive possible resultant WKB type which can result
+     * from subtracting parts of a geometry. A single-point geometry type can never become a multi-point geometry type as
+     * a result of a subtraction, but a single-line or single-polygon geometry CAN become a multipart geometry as a result of subtracting
+     * portions of the geometry.
+     *
+     * \see multiType()
+     * \see singleType()
+     * \since QGIS 3.24
+     */
+    static Type promoteNonPointTypesToMulti( Type type ) SIP_HOLDGIL
+    {
+      switch ( geometryType( type ) )
+      {
+        case QgsWkbTypes::PointGeometry:
+        case QgsWkbTypes::UnknownGeometry:
+        case QgsWkbTypes::NullGeometry:
+          return type;
+
+        case QgsWkbTypes::LineGeometry:
+        case QgsWkbTypes::PolygonGeometry:
+          return multiType( type );
+      }
+      return Unknown;
+    }
+
     /**
      * Returns the curve type for a WKB type. For example, for Polygon WKB types the curve type would be CurvePolygon.
      *

diff --git a/tests/src/python/test_qgsgeometry.py b/tests/src/python/test_qgsgeometry.py
@@ -3154,6 +3154,69 @@ def testWkbTypes(self):
         self.assertEqual(QgsWkbTypes.multiType(QgsWkbTypes.TriangleM), QgsWkbTypes.MultiPolygonM)
         self.assertEqual(QgsWkbTypes.multiType(QgsWkbTypes.TriangleZM), QgsWkbTypes.MultiPolygonZM)
 
+        # test promoteNonPointTypesToMulti method
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.Unknown), QgsWkbTypes.Unknown)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.Point), QgsWkbTypes.Point)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.PointZ), QgsWkbTypes.PointZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.PointM), QgsWkbTypes.PointM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.PointZM), QgsWkbTypes.PointZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPoint), QgsWkbTypes.MultiPoint)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPointZ), QgsWkbTypes.MultiPointZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPointM), QgsWkbTypes.MultiPointM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPointZM), QgsWkbTypes.MultiPointZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.LineString), QgsWkbTypes.MultiLineString)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.LineStringZ), QgsWkbTypes.MultiLineStringZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.LineStringM), QgsWkbTypes.MultiLineStringM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.LineStringZM), QgsWkbTypes.MultiLineStringZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiLineString), QgsWkbTypes.MultiLineString)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiLineStringZ), QgsWkbTypes.MultiLineStringZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiLineStringM), QgsWkbTypes.MultiLineStringM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiLineStringZM), QgsWkbTypes.MultiLineStringZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.Polygon), QgsWkbTypes.MultiPolygon)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.PolygonZ), QgsWkbTypes.MultiPolygonZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.PolygonM), QgsWkbTypes.MultiPolygonM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.PolygonZM), QgsWkbTypes.MultiPolygonZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPolygon), QgsWkbTypes.MultiPolygon)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPolygonZ), QgsWkbTypes.MultiPolygonZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPolygonM), QgsWkbTypes.MultiPolygonM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPolygonZM), QgsWkbTypes.MultiPolygonZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.GeometryCollection), QgsWkbTypes.GeometryCollection)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.GeometryCollectionZ), QgsWkbTypes.GeometryCollectionZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.GeometryCollectionM), QgsWkbTypes.GeometryCollectionM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.GeometryCollectionZM), QgsWkbTypes.GeometryCollectionZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CircularString), QgsWkbTypes.MultiCurve)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CircularStringZ), QgsWkbTypes.MultiCurveZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CircularStringM), QgsWkbTypes.MultiCurveM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CircularStringZM), QgsWkbTypes.MultiCurveZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CompoundCurve), QgsWkbTypes.MultiCurve)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CompoundCurveZ), QgsWkbTypes.MultiCurveZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CompoundCurveM), QgsWkbTypes.MultiCurveM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CompoundCurveZM), QgsWkbTypes.MultiCurveZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CurvePolygon), QgsWkbTypes.MultiSurface)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CurvePolygonZ), QgsWkbTypes.MultiSurfaceZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CurvePolygonM), QgsWkbTypes.MultiSurfaceM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.CurvePolygonZM), QgsWkbTypes.MultiSurfaceZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiCurve), QgsWkbTypes.MultiCurve)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiCurveZ), QgsWkbTypes.MultiCurveZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiCurveM), QgsWkbTypes.MultiCurveM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiCurveZM), QgsWkbTypes.MultiCurveZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiSurface), QgsWkbTypes.MultiSurface)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiSurfaceZ), QgsWkbTypes.MultiSurfaceZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiSurfaceM), QgsWkbTypes.MultiSurfaceM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiSurfaceZM), QgsWkbTypes.MultiSurfaceZM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.NoGeometry), QgsWkbTypes.NoGeometry)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.Point25D), QgsWkbTypes.Point25D)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.LineString25D), QgsWkbTypes.MultiLineString25D)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.Polygon25D), QgsWkbTypes.MultiPolygon25D)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPoint25D), QgsWkbTypes.MultiPoint25D)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiLineString25D), QgsWkbTypes.MultiLineString25D)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.MultiPolygon25D), QgsWkbTypes.MultiPolygon25D)
+        # until we have tin types, these should return multipolygons
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.Triangle), QgsWkbTypes.MultiPolygon)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.TriangleZ), QgsWkbTypes.MultiPolygonZ)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.TriangleM), QgsWkbTypes.MultiPolygonM)
+        self.assertEqual(QgsWkbTypes.promoteNonPointTypesToMulti(QgsWkbTypes.TriangleZM), QgsWkbTypes.MultiPolygonZM)
+
         # test curveType method
         self.assertEqual(QgsWkbTypes.curveType(QgsWkbTypes.Unknown), QgsWkbTypes.Unknown)
         self.assertEqual(QgsWkbTypes.curveType(QgsWkbTypes.Point), QgsWkbTypes.Point)