fix warpimage for projection = 'hammer' (issue 100)

Changelog

@@ -1,3 +1,7 @@
+since version 1.0.6
+-------------------
+* fix warpimage with projection = 'hammer' (issue 100).
+
 version 1.0.6 (git tag v1.0.6rel)
 --------------------------------
 * fix drawcounties for Python 3.3.

examples/warpimage.py

@@ -34,6 +34,19 @@
 plt.title("Blue Marble image warped from 'cyl' to 'mbtfpq' projection",fontsize=12)
 print('warp to McBryde-Thomas Flat-Polar Quartic map ...')
 
+# create new figure
+fig=plt.figure()
+# define projection centered on North America.
+m = Basemap(projection='hammer',lon_0=-100,resolution='l')
+m.bluemarble(scale=0.5)
+# draw coastlines.
+m.drawcoastlines(linewidth=0.5,color='0.5')
+# draw lat/lon grid lines every 30 degrees.
+m.drawmeridians(np.arange(0,360,60),color='0.5')
+m.drawparallels(np.arange(-90,90,30),color='0.5')
+plt.title("Blue Marble image warped from 'cyl' to 'hammer' projection",fontsize=12)
+print('warp to Hammer map ...')
+
 # create new figure
 fig=plt.figure()
 # define cylindrical equidistant projection.

lib/mpl_toolkits/basemap/__init__.py

@@ -3982,6 +3982,9 @@ def warpimage(self,image="bluemarble",scale=None,**kwargs):
         except ImportError:
             raise ImportError('warpimage method requires PIL (http://www.pythonware.com/products/pil)')
         from matplotlib.image import pil_to_array
+        if self.celestial:
+            msg='warpimage does not work in celestial coordinates'
+            raise ValueError(msg)
         ax = kwargs.pop('ax', None) or self._check_ax()
         # default image file is blue marble next generation
         # from NASA (http://visibleearth.nasa.gov).
@@ -4089,7 +4092,8 @@ def warpimage(self,image="bluemarble",scale=None,**kwargs):
                     # make points outside projection limb transparent.
                     self._bm_rgba_warped = self._bm_rgba_warped.filled(0.)
                 # treat pseudo-cyl projections such as mollweide, robinson and sinusoidal.
-                elif self.projection in _pseudocyl:
+                elif self.projection in _pseudocyl and \
+                     self.projection != 'hammer':
                     lonsr,latsr = self(x,y,inverse=True)
                     mask = ma.zeros((ny,nx,4),np.int8)
                     lon_0 = self.projparams['lon_0']
@@ -4112,6 +4116,12 @@ def warpimage(self,image="bluemarble",scale=None,**kwargs):
                     self._bm_rgba_warped = self._bm_rgba_warped.filled(0.)
             # plot warped rgba image.
             im = self.imshow(self._bm_rgba_warped,ax=ax,**kwargs)
+            # for hammer projection, use clip path defined by
+            # projection limb (patch created in drawmapboundary).
+            if self.projection == 'hammer':
+                if not self._mapboundarydrawn:
+                    self.drawmapboundary(color='none',linewidth=None)
+                im.set_clip_path(self._mapboundarydrawn)
         else:
             # bmproj True, no interpolation necessary.
             im = self.imshow(self._bm_rgba,ax=ax,**kwargs)