Fix union with empty polygon.

git-svn-id: http://svn.stsci.edu/svn/ssb/stsci_python/stsci.sphere/trunk@32433 fe389314-cf27-0410-b35b-8c050e845b92

Former-commit-id: ad718756b906e7254f8a899a8683e641e8396c17

3 files changed, 32 insertions, 0 deletions

diff --git a/stsci/sphere/polygon.py b/stsci/sphere/polygon.py
index 2d67ff2..0406402 100644
--- a/stsci/sphere/polygon.py
+++ b/stsci/sphere/polygon.py
@@ -104,6 +104,9 @@ class SphericalPolygon(object):
         return '%s(%r, %r)' % (self.__class__.__name__,
                                self.points, self.inside)
 
+    def copy(self):
+        return self.__class__(self._points.copy(), self._inside.copy())
+
     @property
     def points(self):
         """
@@ -604,6 +607,11 @@ class SphericalPolygon(object):
         module.
         """
         from . import graph
+        if len(self._points) < 3:
+            return other.copy()
+        elif len(other._points) < 3:
+            return self.copy()
+
         g = graph.Graph([self, other])
 
         polygon = g.union()
diff --git a/stsci/sphere/test/test_intersection.py b/stsci/sphere/test/test_intersection.py
index 3576cc1..08ed258 100644
--- a/stsci/sphere/test/test_intersection.py
+++ b/stsci/sphere/test/test_intersection.py
@@ -176,6 +176,18 @@ def test6():
     return [poly1, poly2]
 
 
+def test_union_empty():
+    p = polygon.SphericalPolygon.from_cone(
+        random.randrange(-180, 180),
+        random.randrange(20, 90),
+        random.randrange(5, 16),
+        steps=16)
+
+    p2 = p.intersection(polygon.SphericalPolygon([]))
+
+    assert_array_almost_equal(p2._points, p._points)
+
+
 if __name__ == '__main__':
     if '--profile' not in sys.argv:
         GRAPH_MODE = True
diff --git a/stsci/sphere/test/test_union.py b/stsci/sphere/test/test_union.py
index b106907..24de9e6 100644
--- a/stsci/sphere/test/test_union.py
+++ b/stsci/sphere/test/test_union.py
@@ -214,3 +214,15 @@ if __name__ == '__main__':
     functions.sort()
     for k, v in functions:
         v()
+
+
+def test_union_empty():
+    p = polygon.SphericalPolygon.from_cone(
+        random.randrange(-180, 180),
+        random.randrange(20, 90),
+        random.randrange(5, 16),
+        steps=16)
+
+    p2 = p.union(polygon.SphericalPolygon([]))
+
+    assert_array_almost_equal(p2._points, p._points)