geo.py: fix divide-by-zero warning in Aitoff transform

efiring · efiring · commit 533e5fba0bee · 2011-10-02T12:55:28.000-10:00
An attempt to do this had been make by masking zero values
in the denominator; but at least with current numpy, this is
not enough, because the __div__ method of the first argument
is used.  The solution is to ensure that the first argument
is also a masked array.
diff --git a/lib/matplotlib/projections/geo.py b/lib/matplotlib/projections/geo.py
@@ -271,16 +271,16 @@ def transform(self, ll):
             cos_latitude = np.cos(latitude)
 
             alpha = np.arccos(cos_latitude * np.cos(half_long))
-            # Mask this array, or we'll get divide-by-zero errors
+            # Mask this array or we'll get divide-by-zero errors
             alpha = ma.masked_where(alpha == 0.0, alpha)
+            # The numerators also need to be masked so that masked
+            # division will be invoked.
             # We want unnormalized sinc.  numpy.sinc gives us normalized
             sinc_alpha = ma.sin(alpha) / alpha
 
-            x = (cos_latitude * np.sin(half_long)) / sinc_alpha
-            y = (np.sin(latitude) / sinc_alpha)
-            x.set_fill_value(0.0)
-            y.set_fill_value(0.0)
-            return np.concatenate((x.filled(), y.filled()), 1)
+            x = (cos_latitude * ma.sin(half_long)) / sinc_alpha
+            y = (ma.sin(latitude) / sinc_alpha)
+            return np.concatenate((x.filled(0), y.filled(0)), 1)
         transform.__doc__ = Transform.transform.__doc__
 
         transform_non_affine = transform
