Merge pull request #2225 from rcomer/contourf-paths

FIX: contourf nested contours

lib/cartopy/mpl/patch.py

@@ -168,15 +168,20 @@ def path_to_geos(path, force_ccw=False):
             geom = sgeom.LineString(path_verts)
 
         # If geom is a Polygon and is contained within the last geom in
-        # collection, add it to its list of internal polygons, otherwise
-        # simply append it as a new external geom.
+        # collection, it usually needs to be an interior to that geom (e.g. a
+        # lake within a land mass).  Sometimes there is a further geom within
+        # this interior (e.g. an island in a lake, or some instances of
+        # contours).  This needs to be a new external geom in the collection.
         if geom.is_empty:
             pass
         elif (len(collection) > 0 and
                 isinstance(collection[-1][0], sgeom.Polygon) and
                 isinstance(geom, sgeom.Polygon) and
                 collection[-1][0].contains(geom.exterior)):
-            collection[-1][1].append(geom.exterior)
+            if any(internal.contains(geom) for internal in collection[-1][1]):
+                collection.append((geom, []))
+            else:
+                collection[-1][1].append(geom)
         elif isinstance(geom, sgeom.Point):
             other_result_geoms.append(geom)
         else:
@@ -188,8 +193,8 @@ def path_to_geos(path, force_ccw=False):
     geom_collection = []
     for external_geom, internal_polys in collection:
         if internal_polys:
-            # XXX worry about islands within lakes
-            geom = sgeom.Polygon(external_geom.exterior, internal_polys)
+            exteriors = [geom.exterior for geom in internal_polys]
+            geom = sgeom.Polygon(external_geom.exterior, exteriors)
         else:
             geom = external_geom
 

lib/cartopy/tests/mpl/test_patch.py

@@ -43,3 +43,19 @@ def test_polygon_with_interior_and_singularity(self):
         geoms = cpatch.path_to_geos(p)
         assert [type(geom) for geom in geoms] == [sgeom.Polygon, sgeom.Point]
         assert len(geoms[0].interiors) == 1
+
+    def test_nested_polygons(self):
+        # A geometry with three nested squares.
+        vertices = [[0, 0], [0, 10], [10, 10], [10, 0], [0, 0],
+                    [2, 2], [2, 8], [8, 8], [8, 2], [2, 2],
+                    [4, 4], [4, 6], [6, 6], [6, 4], [4, 4]]
+        codes = [1, 2, 2, 2, 79, 1, 2, 2, 2, 79, 1, 2, 2, 2, 79]
+        p = Path(vertices, codes=codes)
+        geoms = cpatch.path_to_geos(p)
+
+        # The first square makes the first geometry with the second square as
+        # its interior.  The third square is its own geometry with no interior.
+        assert len(geoms) == 2
+        assert all(type(geom) == sgeom.Polygon for geom in geoms)
+        assert len(geoms[0].interiors) == 1
+        assert len(geoms[1].interiors) == 0