change interface of transformation merging

skimage/transform/geometric.py

@@ -105,18 +105,15 @@ class GeometricTransformation(object):
             self.inverse_matrix = np.linalg.inv(self.matrix)
         return geometric_transform(coords, self.inverse_matrix)
 
-    def union(self, other):
+    def __mul__(self, other):
         if type(self) == type(other):
             transformation = self.__class__
         else:
             transformation = GeometricTransformation
         return transformation(self.matrix.dot(other.matrix))
 
-    def __mul__(self, other):
-        return self.union(other)
-
     def __add__(self, other):
-        return self.union(other)
+        return self.__mul__(other)
 
 
 class SimilarityTransformation(GeometricTransformation):
@@ -424,15 +421,6 @@ class PolynomialTransformation(GeometricTransformation):
             'parameters by exchanging source and destination coordinates.'
             'Then apply the forward transformation.')
 
-    def union(self, other):
-        raise Exception('Cannot unite polynomial transformations.')
-
-    def __mul__(self, other):
-        return self.union(self, other)
-
-    def __add__(self, other):
-        return self.union(self, other)
-
 
 TRANSFORMATIONS = {
     'similarity': SimilarityTransformation,

skimage/transform/tests/test_geometric.py

@@ -135,7 +135,6 @@ def test_union():
     translation2 = (0, 0)
     tform2.from_params(scale2, rotation2, translation2)
 
-    tform = tform1.union(tform2)
     tform = tform1 + tform2
     tform = tform1 * tform2