FIX: Allow negative radii in RadialLocator and polar grids.

QuLogic · QuLogic · commit 52ab847fb6c3 · 2017-08-15T22:19:30.000-04:00
Polar axes do not have any issue with negative radii; the plotting axes
are simply shifted so that the minimum radius of the data occurs at r=0
in plotting space.

For all-positive radii, the RadialLocator will preferentially choose 0
as the minimum view limit to remain backwards compatible with the
previous version. If any radii are negative, then the usual minimum is
used.
diff --git a/lib/matplotlib/projections/polar.py b/lib/matplotlib/projections/polar.py
@@ -192,12 +192,21 @@ class RadialLocator(Locator):
     :class:`~matplotlib.ticker.Locator` (which may be different
     depending on the scale of the *r*-axis.
     """
-    def __init__(self, base):
+    def __init__(self, base, axes=None):
         self.base = base
+        self._axes = axes
 
     def __call__(self):
-        ticks = self.base()
-        return [x for x in ticks if x > 0]
+        show_all = True
+        # Ensure previous behaviour with full circle views.
+        if self._axes:
+            rmin = self._axes.get_rmin()
+            show_all = False
+
+        if show_all:
+            return self.base()
+        else:
+            return [tick for tick in self.base() if tick > rmin]
 
     def autoscale(self):
         return self.base.autoscale()
@@ -213,7 +222,7 @@ def refresh(self):
 
     def view_limits(self, vmin, vmax):
         vmin, vmax = self.base.view_limits(vmin, vmax)
-        return 0, vmax
+        return min(0, vmin), vmax
 
 
 class PolarAxes(Axes):
@@ -246,7 +255,8 @@ def cla(self):
         self.xaxis.isDefault_majfmt = True
         angles = np.arange(0.0, 360.0, 45.0)
         self.set_thetagrids(angles)
-        self.yaxis.set_major_locator(self.RadialLocator(self.yaxis.get_major_locator()))
+        self.yaxis.set_major_locator(
+            self.RadialLocator(self.yaxis.get_major_locator(), self))
 
         self.grid(rcParams['polaraxes.grid'])
         self.xaxis.set_ticks_position('none')
@@ -473,7 +483,7 @@ def set_rlabel_position(self, value):
     def set_yscale(self, *args, **kwargs):
         Axes.set_yscale(self, *args, **kwargs)
         self.yaxis.set_major_locator(
-            self.RadialLocator(self.yaxis.get_major_locator()))
+            self.RadialLocator(self.yaxis.get_major_locator(), self))
 
     def set_rscale(self, *args, **kwargs):
         return Axes.set_yscale(self, *args, **kwargs)
@@ -549,9 +559,6 @@ def set_rgrids(self, radii, labels=None, angle=None, fmt=None,
         # Make sure we take into account unitized data
         radii = self.convert_xunits(radii)
         radii = np.asarray(radii)
-        rmin = radii.min()
-        if rmin <= 0:
-            raise ValueError('radial grids must be strictly positive')
 
         self.set_yticks(radii)
         if labels is not None:
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -624,6 +624,18 @@ def test_polar_rmin():
     ax.set_rmin(0.5)
 
 
+@image_comparison(baseline_images=['polar_negative_rmin'], style='default')
+def test_polar_negative_rmin():
+    r = np.arange(-3.0, 0.0, 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_rmax(0.0)
+    ax.set_rmin(-3.0)
+
+
 @image_comparison(baseline_images=['polar_theta_position'])
 def test_polar_theta_position():
     r = np.arange(0, 3.0, 0.01)
