Simplify radar_chart example.

anntzer · anntzer · commit 7c4d7f712e00 · 2018-10-11T17:00:31.000+02:00
... by reusing already existing utilities to generate regular polygons.
diff --git a/examples/specialty_plots/radar_chart.py b/examples/specialty_plots/radar_chart.py
@@ -13,13 +13,16 @@
 
 .. [1] http://en.wikipedia.org/wiki/Radar_chart
 """
+
 import numpy as np
 
 import matplotlib.pyplot as plt
+from matplotlib.patches import Circle, RegularPolygon
 from matplotlib.path import Path
-from matplotlib.spines import Spine
 from matplotlib.projections.polar import PolarAxes
 from matplotlib.projections import register_projection
+from matplotlib.spines import Spine
+from matplotlib.transforms import Affine2D
 
 
 def radar_factory(num_vars, frame='circle'):
@@ -38,14 +41,14 @@ def radar_factory(num_vars, frame='circle'):
     # calculate evenly-spaced axis angles
     theta = np.linspace(0, 2*np.pi, num_vars, endpoint=False)
 
+    # The Axes patch must be centered at (0.5, 0.5) and of radius 0.5 in axes
+    # coordinates.
+
     def draw_poly_patch(self):
-        # rotate theta such that the first axis is at the top
-        verts = unit_poly_verts(theta + np.pi / 2)
-        return plt.Polygon(verts, closed=True, edgecolor='k')
+        return RegularPolygon((0.5, 0.5), num_vars, radius=.5, edgecolor="k")
 
     def draw_circle_patch(self):
-        # unit circle centered on (0.5, 0.5)
-        return plt.Circle((0.5, 0.5), 0.5)
+        return Circle((0.5, 0.5), 0.5)
 
     patch_dict = {'polygon': draw_poly_patch, 'circle': draw_circle_patch}
     if frame not in patch_dict:
@@ -94,31 +97,21 @@ def _gen_axes_spines(self):
             # The following is a hack to get the spines (i.e. the axes frame)
             # to draw correctly for a polygon frame.
 
-            # spine_type must be 'left', 'right', 'top', 'bottom', or `circle`.
-            spine_type = 'circle'
-            verts = unit_poly_verts(theta + np.pi / 2)
-            # close off polygon by repeating first vertex
-            verts.append(verts[0])
-            path = Path(verts)
-
-            spine = Spine(self, spine_type, path)
-            spine.set_transform(self.transAxes)
+            # spine_type must be 'left', 'right', 'top', 'bottom', or 'circle'.
+            spine = Spine(axes=self,
+                          spine_type='circle',
+                          path=Path.unit_regular_polygon(num_vars))
+            # unit_regular_polygon gives a polygon of radius 1 centered at
+            # (0, 0) but we want a polygon of radius 0.5 centerer at (0.5, 0.5)
+            # in axes coordinates.
+            spine.set_transform(Affine2D().scale(.5).translate(.5, .5)
+                                + self.transAxes)
             return {'polar': spine}
 
     register_projection(RadarAxes)
     return theta
 
 
-def unit_poly_verts(theta):
-    """Return vertices of polygon for subplot axes.
-
-    This polygon is circumscribed by a unit circle centered at (0.5, 0.5)
-    """
-    x0, y0, r = [0.5] * 3
-    verts = [(r*np.cos(t) + x0, r*np.sin(t) + y0) for t in theta]
-    return verts
-
-
 def example_data():
     # The following data is from the Denver Aerosol Sources and Health study.
     # See doi:10.1016/j.atmosenv.2008.12.017
