Fixed #25654 -- Added the GEOSGeometry.unary_union property.

django/contrib/gis/geos/geometry.py

@@ -621,6 +621,11 @@ class GEOSGeometry(GEOSBase, ListMixin):
         """
         return self._topology(capi.geos_symdifference(self.ptr, other.ptr))
 
+    @property
+    def unary_union(self):
+        "Return the union of all the elements of this geometry."
+        return self._topology(capi.geos_unary_union(self.ptr))
+
     def union(self, other):
         "Returns a Geometry representing all the points in this Geometry and other."
         return self._topology(capi.geos_union(self.ptr, other.ptr))

django/contrib/gis/geos/prototypes/topology.py

@@ -34,6 +34,7 @@ geos_symdifference = Topology('GEOSSymDifference', argtypes=[GEOM_PTR, GEOM_PTR]
 geos_union = Topology('GEOSUnion', argtypes=[GEOM_PTR, GEOM_PTR])
 
 geos_cascaded_union = GEOSFuncFactory('GEOSUnionCascaded', argtypes=[GEOM_PTR], restype=GEOM_PTR)
+geos_unary_union = GEOSFuncFactory('GEOSUnaryUnion', argtypes=[GEOM_PTR], restype=GEOM_PTR)
 
 # GEOSRelate returns a string, not a geometry.
 geos_relate = GEOSFuncFactory(

docs/ref/contrib/gis/geos.txt

@@ -497,6 +497,21 @@ geometry is a point.
 Computes and returns a :class:`Point` guaranteed to be on the interior
 of this geometry.
 
+.. attribute:: GEOSGeometry.unary_union
+
+.. versionadded:: 1.10
+
+Computes the union of all the elements of this geometry.
+
+The result obeys the following contract:
+
+* Unioning a set of :class:`LineString`\s has the effect of fully noding and
+  dissolving the linework.
+
+* Unioning a set of :class:`Polygon`\s will always return a :class:`Polygon` or
+  :class:`MultiPolygon` geometry (unlike :meth:`GEOSGeometry.union`, which may
+  return geometries of lower dimension if a topology collapse occurs).
+
 Other Properties & Methods
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 

docs/releases/1.10.txt

@@ -64,6 +64,10 @@ Minor features
 * :ref:`Distance lookups <distance-lookups>` now accept expressions as the
   distance value parameter.
 
+* The new :attr:`GEOSGeometry.unary_union
+  <django.contrib.gis.geos.GEOSGeometry.unary_union>` property computes the
+  union of all the elements of this geometry.
+
 :mod:`django.contrib.messages`
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

docs/spelling_wordlist

@@ -421,6 +421,7 @@ linebreaks
 linebreaksbr
 linenumbers
 linestring
+linework
 Livni
 ljust
 loaddata
@@ -520,6 +521,7 @@ nestable
 neuroscientist
 newforms
 nginx
+noding
 nonspatial
 nullable
 OAuth
@@ -877,6 +879,7 @@ unicode
 uninstall
 uninstalling
 uninstalls
+unioning
 uniterated
 unittest
 unittests

tests/gis_tests/geos_tests/test_geos.py

@@ -582,6 +582,15 @@ class GEOSTest(SimpleTestCase, TestDataMixin):
             a |= b  # testing __ior__
             self.assertEqual(u1, a)
 
+    def test_unary_union(self):
+        "Testing unary_union."
+        for i in range(len(self.geometries.topology_geoms)):
+            a = fromstr(self.geometries.topology_geoms[i].wkt_a)
+            b = fromstr(self.geometries.topology_geoms[i].wkt_b)
+            u1 = fromstr(self.geometries.union_geoms[i].wkt)
+            u2 = GeometryCollection(a, b).unary_union
+            self.assertTrue(u1.equals(u2))
+
     def test_difference(self):
         "Testing difference()."
         for i in range(len(self.geometries.topology_geoms)):