Fix bug in polar plots: if rmax - rmin was too small, the old rpad padding heuristic broke down and sent the rlabels way off of the plot axes. The new approach is to not have rpad, but to change the alignment of the rlabels depending on the quadrant of the plot. This seems to work quite well, but is perhaps slightly backward incompatible.

Author: mdboom

CHANGELOG

@@ -1,12 +1,18 @@
 2012-02-29 errorevery keyword added to errorbar to enable errorbar
            subsampling. fixes issue #600.
 
+2012-01-23 The radius labels in polar plots no longer use a fixed
+           padding, but use a different alignment depending on the
+           quadrant they are in.  This fixes numerical problems when
+           (rmax - rmin) gets too small. - MGD
+
 2012-01-08 Add axes.streamplot to plot streamlines of a velocity field.
 		   Adapted from Tom Flannaghan streamplot implementation. -TSY
 
 2011-12-29 ps and pdf markers are now stroked only if the line width
            is nonzero for consistency with agg, fixes issue #621. - JKS
 
+
 2011-12-27 Work around an EINTR bug in some versions of subprocess. - JKS
 
 

lib/matplotlib/projections/polar.py

@@ -63,7 +63,7 @@ def transform(self, tr):
 
             t *= theta_direction
             t += theta_offset
-            
+
             if rmin != 0:
                 r = r - rmin
                 mask = r < 0
@@ -150,7 +150,7 @@ def transform(self, xy):
                 rmin = 0
                 theta_offset = 0
                 theta_direction = 1
-            
+
             x = xy[:, 0:1]
             y = xy[:, 1:]
             r = np.sqrt(x*x + y*y)
@@ -161,7 +161,7 @@ def transform(self, xy):
             theta *= theta_direction
 
             r += rmin
-            
+
             return np.concatenate((theta, r), 1)
         transform.__doc__ = Transform.transform.__doc__
 
@@ -230,7 +230,6 @@ def __init__(self, *args, **kwargs):
             interpolation.
         """
 
-        self._rpad = 0.05
         self.resolution = kwargs.pop('resolution', None)
         if self.resolution not in (None, 1):
             warnings.warn(
@@ -262,7 +261,7 @@ def cla(self):
 
         self.set_theta_offset(0)
         self.set_theta_direction(1)
-        
+
     def _init_axis(self):
         "move this out of __init__ because non-separable axes don't use it"
         self.xaxis = maxis.XAxis(self)
@@ -320,21 +319,10 @@ def _set_lim_and_transforms(self):
             Affine2D().scale(np.pi * 2.0, 1.0) +
             self.transData)
         # The r-axis labels are put at an angle and padded in the r-direction
-        self._r_label1_position = ScaledTranslation(
-            22.5, self._rpad,
-            blended_transform_factory(
-                Affine2D(), BboxTransformToMaxOnly(self.viewLim)))
-        self._yaxis_text1_transform = (
-            self._r_label1_position +
-            Affine2D().scale(1.0 / 360.0, 1.0) +
-            self._yaxis_transform
-            )
-        self._r_label2_position = ScaledTranslation(
-            22.5, -self._rpad,
-            blended_transform_factory(
-                Affine2D(), BboxTransformToMaxOnly(self.viewLim)))
-        self._yaxis_text2_transform = (
-            self._r_label2_position +
+        self._r_label_position = ScaledTranslation(
+            22.5, 0.0, Affine2D())
+        self._yaxis_text_transform = (
+            self._r_label_position +
             Affine2D().scale(1.0 / 360.0, 1.0) +
             self._yaxis_transform
             )
@@ -354,10 +342,26 @@ def get_yaxis_transform(self,which='grid'):
         return self._yaxis_transform
 
     def get_yaxis_text1_transform(self, pad):
-        return self._yaxis_text1_transform, 'center', 'center'
+        angle = self._r_label_position.to_values()[4]
+        if angle < 90.:
+            return self._yaxis_text_transform, 'bottom', 'left'
+        elif angle < 180.:
+            return self._yaxis_text_transform, 'bottom', 'right'
+        elif angle < 270.:
+            return self._yaxis_text_transform, 'top', 'right'
+        else:
+            return self._yaxis_text_transform, 'top', 'left'
 
     def get_yaxis_text2_transform(self, pad):
-        return self._yaxis_text2_transform, 'center', 'center'
+        angle = self._r_label_position.to_values()[4]
+        if angle < 90.:
+            return self._yaxis_text_transform, 'top', 'right'
+        elif angle < 180.:
+            return self._yaxis_text_transform, 'top', 'left'
+        elif angle < 270.:
+            return self._yaxis_text_transform, 'bottom', 'left'
+        else:
+            return self._yaxis_text_transform, 'bottom', 'right'
 
     def _gen_axes_patch(self):
         return Circle((0.5, 0.5), 0.5)
@@ -407,7 +411,7 @@ def set_theta_zero_location(self, loc):
             'E': 0,
             'NE': np.pi * 0.25 }
         return self.set_theta_offset(mapping[loc])
-    
+
     def set_theta_direction(self, direction):
         """
         Set the direction in which theta increases.
@@ -438,7 +442,7 @@ def get_theta_direction(self):
            Theta increases in the counterclockwise direction
         """
         return self._direction
-        
+
     def set_rlim(self, *args, **kwargs):
         if 'rmin' in kwargs:
             kwargs['ymin'] = kwargs.pop('rmin')
@@ -497,7 +501,7 @@ def set_thetagrids(self, angles, labels=None, frac=None, fmt=None,
         return self.xaxis.get_ticklines(), self.xaxis.get_ticklabels()
 
     @docstring.dedent_interpd
-    def set_rgrids(self, radii, labels=None, angle=None, rpad=None, fmt=None,
+    def set_rgrids(self, radii, labels=None, angle=None, fmt=None,
                    **kwargs):
         """
         Set the radial locations and labels of the *r* grids.
@@ -510,9 +514,6 @@ def set_rgrids(self, radii, labels=None, angle=None, rpad=None, fmt=None,
 
         If *labels* is None, the built-in formatter will be used.
 
-        *rpad* is a fraction of the max of *radii* which will pad each of
-        the radial labels in the radial direction.
-
         Return value is a list of tuples (*line*, *label*), where
         *line* is :class:`~matplotlib.lines.Line2D` instances and the
         *label* is :class:`~matplotlib.text.Text` instances.
@@ -536,13 +537,9 @@ def set_rgrids(self, radii, labels=None, angle=None, rpad=None, fmt=None,
         elif fmt is not None:
             self.yaxis.set_major_formatter(FormatStrFormatter(fmt))
         if angle is None:
-            angle = self._r_label1_position.to_values()[4]
-        if rpad is not None:
-            self._rpad = rpad
-        self._r_label1_position._t = (angle, self._rpad)
-        self._r_label1_position.invalidate()
-        self._r_label2_position._t = (angle, -self._rpad)
-        self._r_label2_position.invalidate()
+            angle = self._r_label_position.to_values()[4]
+        self._r_label_position._t = (angle, 0.0)
+        self._r_label_position.invalidate()
         for t in self.yaxis.get_ticklabels():
             t.update(kwargs)
         return self.yaxis.get_gridlines(), self.yaxis.get_ticklabels()
@@ -594,7 +591,7 @@ def can_pan(self) :
         return True
 
     def start_pan(self, x, y, button):
-        angle = self._r_label1_position.to_values()[4] / 180.0 * np.pi
+        angle = np.deg2rad(self._r_label_position.to_values()[4])
         mode = ''
         if button == 1:
             epsilon = np.pi / 45.0
@@ -608,7 +605,7 @@ def start_pan(self, x, y, button):
             rmax          = self.get_rmax(),
             trans         = self.transData.frozen(),
             trans_inverse = self.transData.inverted().frozen(),
-            r_label_angle = self._r_label1_position.to_values()[4],
+            r_label_angle = self._r_label_position.to_values()[4],
             x             = x,
             y             = y,
             mode          = mode
@@ -633,11 +630,16 @@ def drag_pan(self, button, key, x, y):
                 dt = dt0 * -1.0
             dt = (dt / np.pi) * 180.0
 
-            rpad = self._rpad
-            self._r_label1_position._t = (p.r_label_angle - dt, rpad)
-            self._r_label1_position.invalidate()
-            self._r_label2_position._t = (p.r_label_angle - dt, -rpad)
-            self._r_label2_position.invalidate()
+            self._r_label_position._t = (p.r_label_angle - dt, 0.0)
+            self._r_label_position.invalidate()
+
+            trans, vert1, horiz1 = self.get_yaxis_text1_transform(0.0)
+            trans, vert2, horiz2 = self.get_yaxis_text2_transform(0.0)
+            for t in self.yaxis.majorTicks + self.yaxis.minorTicks:
+                t.label1.set_va(vert1)
+                t.label1.set_ha(horiz1)
+                t.label2.set_va(vert2)
+                t.label2.set_ha(horiz2)
 
         elif p.mode == 'zoom':
             startt, startr = p.trans_inverse.transform_point((p.x, p.y))