SF.net SVN: matplotlib:[8217] trunk/matplotlib/lib/matplotlib/quiver.py

[<ry...@us...>]

Revision: 8217
          http://matplotlib.svn.sourceforge.net/matplotlib/?rev=8217&view=rev
Author:   ryanmay
Date:     2010-04-02 18:47:00 +0000 (Fri, 02 Apr 2010)

Log Message:
-----------
Correct calculation of vectors with quiver and angles='xy'. Using just a small eps can result in roundoff problems if X,Y are large (such as with Basemap).

Modified Paths:
--------------
    trunk/matplotlib/lib/matplotlib/quiver.py

Modified: trunk/matplotlib/lib/matplotlib/quiver.py
===================================================================
--- trunk/matplotlib/lib/matplotlib/quiver.py	2010-04-01 03:41:24 UTC (rev 8216)
+++ trunk/matplotlib/lib/matplotlib/quiver.py	2010-04-02 18:47:00 UTC (rev 8217)
@@ -537,10 +537,11 @@
             # points, regardless of the axis scaling (including log).
             angles, lengths = self._angles_lengths(U, V, eps=1)
         elif self.angles == 'xy' or self.scale_units == 'xy':
-            # We could refine this by calculating eps based on
-            # the magnitude of U, V relative to that of X, Y,
-            # to ensure we are always making small shifts in X, Y.
-            angles, lengths = self._angles_lengths(U, V, eps=0.001)
+            # Calculate eps based on the extents of the plot
+            # so that we don't end up with roundoff error from
+            # adding a small number to a large.
+            angles, lengths = self._angles_lengths(U, V,
+                eps=np.abs(self.ax.dataLim.extents).max() * 0.001)
         if self.scale_units == 'xy':
             a = lengths
         else:


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