Refs #35058 -- Added is_3d and set_3d() to OGRGeometry.

django/contrib/gis/gdal/geometries.py

@@ -268,6 +268,20 @@ class OGRGeometry(GDALBase):
         "Return the envelope as a 4-tuple, instead of as an Envelope object."
         return self.envelope.tuple
 
+    @property
+    def is_3d(self):
+        """Return True if the geometry has Z coordinates."""
+        return capi.is_3d(self.ptr)
+
+    def set_3d(self, value):
+        """Set if this geometry has Z coordinates."""
+        if value is True:
+            capi.set_3d(self.ptr, 1)
+        elif value is False:
+            capi.set_3d(self.ptr, 0)
+        else:
+            raise ValueError(f"Input to 'set_3d' must be a boolean, got '{value!r}'.")
+
     # #### SpatialReference-related Properties ####
 
     # The SRS property
@@ -546,16 +560,15 @@ class Point(OGRGeometry):
     @property
     def z(self):
         "Return the Z coordinate for this Point."
-        if self.coord_dim == 3:
+        if self.is_3d:
             return capi.getz(self.ptr, 0)
 
     @property
     def tuple(self):
         "Return the tuple of this point."
-        if self.coord_dim == 2:
-            return (self.x, self.y)
-        elif self.coord_dim == 3:
+        if self.is_3d:
             return (self.x, self.y, self.z)
+        return self.x, self.y
 
     coords = tuple
 
@@ -566,13 +579,13 @@ class LineString(OGRGeometry):
         if 0 <= index < self.point_count:
             x, y, z = c_double(), c_double(), c_double()
             capi.get_point(self.ptr, index, byref(x), byref(y), byref(z))
+            if self.is_3d:
+                return x.value, y.value, z.value
             dim = self.coord_dim
             if dim == 1:
                 return (x.value,)
             elif dim == 2:
                 return (x.value, y.value)
-            elif dim == 3:
-                return (x.value, y.value, z.value)
         else:
             raise IndexError(
                 "Index out of range when accessing points of a line string: %s." % index
@@ -609,7 +622,7 @@ class LineString(OGRGeometry):
     @property
     def z(self):
         "Return the Z coordinates in a list."
-        if self.coord_dim == 3:
+        if self.is_3d:
             return self._listarr(capi.getz)
 
 

django/contrib/gis/gdal/prototypes/geom.py

@@ -4,6 +4,7 @@ from django.contrib.gis.gdal.envelope import OGREnvelope
 from django.contrib.gis.gdal.libgdal import GDAL_VERSION, lgdal
 from django.contrib.gis.gdal.prototypes.errcheck import check_envelope
 from django.contrib.gis.gdal.prototypes.generation import (
+    bool_output,
     const_string_output,
     double_output,
     geom_output,
@@ -79,6 +80,8 @@ geom_diff = geom_output(lgdal.OGR_G_Difference, [c_void_p, c_void_p])
 geom_intersection = geom_output(lgdal.OGR_G_Intersection, [c_void_p, c_void_p])
 geom_sym_diff = geom_output(lgdal.OGR_G_SymmetricDifference, [c_void_p, c_void_p])
 geom_union = geom_output(lgdal.OGR_G_Union, [c_void_p, c_void_p])
+is_3d = bool_output(lgdal.OGR_G_Is3D, [c_void_p])
+set_3d = void_output(lgdal.OGR_G_Set3D, [c_void_p, c_int], errcheck=False)
 
 # Geometry modification routines.
 add_geom = void_output(lgdal.OGR_G_AddGeometry, [c_void_p, c_void_p])

django/contrib/gis/utils/layermapping.py

@@ -489,8 +489,8 @@ class LayerMapping:
         the mapped shapefile only contains Polygons).
         """
         # Downgrade a 3D geom to a 2D one, if necessary.
-        if self.coord_dim != geom.coord_dim:
-            geom.coord_dim = self.coord_dim
+        if self.coord_dim == 2 and geom.is_3d:
+            geom.set_3d(False)
 
         if self.make_multi(geom.geom_type, model_field):
             # Constructing a multi-geometry type to contain the single geometry

docs/ref/contrib/gis/gdal.txt

@@ -556,6 +556,27 @@ coordinate transformation:
     Returns or sets the coordinate dimension of this geometry. For example, the
     value would be 2 for two-dimensional geometries.
 
+    .. attribute:: is_3d
+
+    .. versionadded:: 5.1
+
+    A boolean indicating if this geometry has Z coordinates.
+
+    .. method:: set_3d(value)
+
+    .. versionadded:: 5.1
+
+    A method that adds or removes the Z coordinate dimension.
+
+    .. code-block:: pycon
+
+        >>> p = OGRGeometry("POINT (1 2 3)")
+        >>> p.is_3d
+        True
+        >>> p.set_3d(False)
+        >>> p.wkt
+        "POINT (1 2)"
+
     .. attribute:: geom_count
 
     Returns the number of elements in this geometry:

docs/releases/5.1.txt

@@ -72,6 +72,12 @@ Minor features
 
 * :class:`~django.contrib.gis.measure.Area` now supports the ``ha`` unit.
 
+* The new :attr:`.OGRGeometry.is_3d` attribute allows checking if a geometry
+  has a ``Z`` coordinate dimension.
+
+* The new :meth:`.OGRGeometry.set_3d` method allows addition and removal of the
+  ``Z`` coordinate dimension.
+
 :mod:`django.contrib.messages`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

tests/gis_tests/gdal_tests/test_geom.py

@@ -714,3 +714,16 @@ class OGRGeomTest(SimpleTestCase, TestDataMixin):
                     msg = f"Unsupported geometry type: {type_}"
                     with self.assertRaisesMessage(TypeError, msg):
                         OGRGeometry(f"{geom_type} EMPTY")
+
+    def test_is_3d_and_set_3d(self):
+        geom = OGRGeometry("POINT (1 2)")
+        self.assertIs(geom.is_3d, False)
+        geom.set_3d(True)
+        self.assertIs(geom.is_3d, True)
+        self.assertEqual(geom.wkt, "POINT (1 2 0)")
+        geom.set_3d(False)
+        self.assertIs(geom.is_3d, False)
+        self.assertEqual(geom.wkt, "POINT (1 2)")
+        msg = "Input to 'set_3d' must be a boolean, got 'None'"
+        with self.assertRaisesMessage(ValueError, msg):
+            geom.set_3d(None)