Fixed #15165 -- Prevented wrong results with perimeter on geodetic fields.

django/contrib/gis/db/backends/base/features.py

@@ -26,9 +26,10 @@ class BaseSpatialFeatures(object):
     supports_real_shape_operations = True
     # Can geometry fields be null?
     supports_null_geometries = True
-    # Can the `distance`/`length` functions be applied on geodetic coordinate systems?
+    # Can the the function be applied on geodetic coordinate systems?
     supports_distance_geodetic = True
     supports_length_geodetic = True
+    supports_perimeter_geodetic = False
     # Is the database able to count vertices on polygons (with `num_points`)?
     supports_num_points_poly = True
 

django/contrib/gis/db/backends/oracle/features.py

@@ -7,3 +7,4 @@ class DatabaseFeatures(BaseSpatialFeatures, OracleDatabaseFeatures):
     supports_add_srs_entry = False
     supports_geometry_field_introspection = False
     supports_geometry_field_unique_index = False
+    supports_perimeter_geodetic = True

django/contrib/gis/db/models/functions.py

@@ -206,6 +206,9 @@ class Difference(OracleToleranceMixin, GeoFuncWithGeoParam):
 
 
 class DistanceResultMixin(object):
+    def source_is_geography(self):
+        return self.get_source_fields()[0].geography and self.srid == 4326
+
     def convert_value(self, value, expression, connection, context):
         if value is None:
             return None
@@ -236,9 +239,7 @@ class Distance(DistanceResultMixin, OracleToleranceMixin, GeoFuncWithGeoParam):
 
     def as_postgresql(self, compiler, connection):
         geo_field = GeometryField(srid=self.srid)  # Fake field to get SRID info
-        src_field = self.get_source_fields()[0]
-        geography = src_field.geography and self.srid == 4326
-        if geography:
+        if self.source_is_geography():
             # Set parameters as geography if base field is geography
             for pos, expr in enumerate(
                     self.source_expressions[self.geom_param_pos + 1:], start=self.geom_param_pos + 1):
@@ -297,9 +298,7 @@ class Length(DistanceResultMixin, OracleToleranceMixin, GeoFunc):
 
     def as_postgresql(self, compiler, connection):
         geo_field = GeometryField(srid=self.srid)  # Fake field to get SRID info
-        src_field = self.get_source_fields()[0]
-        geography = src_field.geography and self.srid == 4326
-        if geography:
+        if self.source_is_geography():
             self.source_expressions.append(Value(self.spheroid))
         elif geo_field.geodetic(connection):
             # Geometry fields with geodetic (lon/lat) coordinates need length_spheroid
@@ -346,11 +345,20 @@ class Perimeter(DistanceResultMixin, OracleToleranceMixin, GeoFunc):
     arity = 1
 
     def as_postgresql(self, compiler, connection):
+        geo_field = GeometryField(srid=self.srid)  # Fake field to get SRID info
+        if geo_field.geodetic(connection) and not self.source_is_geography():
+            raise NotImplementedError("ST_Perimeter cannot use a non-projected non-geography field.")
         dim = min(f.dim for f in self.get_source_fields())
         if dim > 2:
             self.function = connection.ops.perimeter3d
         return super(Perimeter, self).as_sql(compiler, connection)
 
+    def as_sqlite(self, compiler, connection):
+        geo_field = GeometryField(srid=self.srid)  # Fake field to get SRID info
+        if geo_field.geodetic(connection):
+            raise NotImplementedError("Perimeter cannot use a non-projected field.")
+        return super(Perimeter, self).as_sql(compiler, connection)
+
 
 class PointOnSurface(OracleToleranceMixin, GeoFunc):
     arity = 1

tests/gis_tests/distapp/tests.py

@@ -444,6 +444,8 @@ Distance_Sphere(geom1, geom2)                 |    N/A             |   OK (meter
 
 Distance_Spheroid(geom1, geom2, spheroid)     |    N/A             |   OK (meters)    |    N/A
 
+ST_Perimeter(geom1)                           |    OK              |   :-( (degrees)  |    OK
+
 
 ================================
 Distance functions on Spatialite
@@ -457,6 +459,8 @@ ST_Distance(geom1, geom2, use_ellipsoid=True)   |    N/A             |      OK (
 
 ST_Distance(geom1, geom2, use_ellipsoid=False)  |    N/A             |      OK (meters), less accurate, quick
 
+Perimeter(geom1)                                |    OK              |      :-( (degrees)
+
 '''  # NOQA
 
 
@@ -688,6 +692,20 @@ class DistanceFunctionsTests(TestCase):
         for city in qs:
             self.assertEqual(0, city.perim.m)
 
+    @skipUnlessDBFeature("has_Perimeter_function")
+    def test_perimeter_geodetic(self):
+        # Currently only Oracle supports calculating the perimeter on geodetic
+        # geometries (without being transformed).
+        qs1 = CensusZipcode.objects.annotate(perim=Perimeter('poly'))
+        if connection.features.supports_perimeter_geodetic:
+            self.assertAlmostEqual(qs1[0].perim.m, 18406.3818954314, 3)
+        else:
+            with self.assertRaises(NotImplementedError):
+                list(qs1)
+        # But should work fine when transformed to projected coordinates
+        qs2 = CensusZipcode.objects.annotate(perim=Perimeter(Transform('poly', 32140))).filter(name='77002')
+        self.assertAlmostEqual(qs2[0].perim.m, 18404.355, 3)
+
     @skipUnlessDBFeature("supports_null_geometries", "has_Area_function", "has_Distance_function")
     def test_measurement_null_fields(self):
         """