ENH: Allow offsetting PolarAxes' zero location.

QuLogic · QuLogic · commit b47ccba3c2d5 · 2017-08-15T23:04:05.000-04:00
Let the user specify an arbitrary zero location with reference to the
usual cardinal points. This can be a bit more intuitive than requiring
the offset in radians.
diff --git a/lib/matplotlib/projections/polar.py b/lib/matplotlib/projections/polar.py
@@ -694,12 +694,18 @@ def get_theta_offset(self):
         """
         return self._theta_offset.get_matrix()[0, 2]
 
-    def set_theta_zero_location(self, loc):
+    def set_theta_zero_location(self, loc, offset=0.0):
         """
         Sets the location of theta's zero.  (Calls set_theta_offset
         with the correct value in radians under the hood.)
 
-        May be one of "N", "NW", "W", "SW", "S", "SE", "E", or "NE".
+        loc : str
+            May be one of "N", "NW", "W", "SW", "S", "SE", "E", or "NE".
+
+        offset : float, optional
+            An offset in degrees to apply from the specified `loc`. **Note:**
+            this offset is *always* applied counter-clockwise regardless of
+            the direction setting.
         """
         mapping = {
             'N': np.pi * 0.5,
@@ -710,7 +716,7 @@ def set_theta_zero_location(self, loc):
             'SE': np.pi * 1.75,
             'E': 0,
             'NE': np.pi * 0.25 }
-        return self.set_theta_offset(mapping[loc])
+        return self.set_theta_offset(mapping[loc] + np.deg2rad(offset))
 
     def set_theta_direction(self, direction):
         """
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -649,15 +649,15 @@ def test_polar_rorigin():
     ax.set_rorigin(0.0)
 
 
-@image_comparison(baseline_images=['polar_theta_position'])
+@image_comparison(baseline_images=['polar_theta_position'], style='default')
 def test_polar_theta_position():
     r = np.arange(0, 3.0, 0.01)
     theta = 2*np.pi*r
 
     fig = plt.figure()
     ax = fig.add_axes([0.1, 0.1, 0.8, 0.8], polar=True)
     ax.plot(theta, r)
-    ax.set_theta_zero_location("NW")
+    ax.set_theta_zero_location("NW", 30)
     ax.set_theta_direction('clockwise')
 
 
