Merge pull request matplotlib#5620 from tacaswell/fix_quiverkey

FIX: quiver key pivot location

Author: efiring

lib/matplotlib/quiver.py

@@ -228,7 +228,7 @@ class QuiverKey(martist.Artist):
     """ Labelled arrow for use as a quiver plot scale key."""
     halign = {'N': 'center', 'S': 'center', 'E': 'left', 'W': 'right'}
     valign = {'N': 'bottom', 'S': 'top', 'E': 'center', 'W': 'center'}
-    pivot = {'N': 'mid', 'S': 'mid', 'E': 'tip', 'W': 'tail'}
+    pivot = {'N': 'middle', 'S': 'middle', 'E': 'tip', 'W': 'tail'}
 
     def __init__(self, Q, X, Y, U, label, **kw):
         martist.Artist.__init__(self)
@@ -708,6 +708,10 @@ def _h_arrows(self, length):
             X = X - X[:, 3, np.newaxis]   # numpy bug? using -= does not
                                           # work here unless we multiply
                                           # by a float first, as with 'mid'.
+        elif self.pivot != 'tail':
+            raise ValueError(("Quiver.pivot must have value in {{'middle', "
+                              "'tip', 'tail'}} not {}").format(self.pivot))
+
         tooshort = length < self.minlength
         if tooshort.any():
             # Use a heptagonal dot:

lib/matplotlib/tests/baseline_images/test_quiver/quiver_key_pivot.png

@@ -92,6 +92,22 @@ def test_quiver_copy():
     assert q0.V[0] == 2.0
 
 
+@image_comparison(baseline_images=['quiver_key_pivot'],
+                  extensions=['png'], remove_text=True)
+def test_quiver_key_pivot():
+    fig, ax = plt.subplots()
+
+    u, v = np.mgrid[0:2*np.pi:10j, 0:2*np.pi:10j]
+
+    q = ax.quiver(np.sin(u), np.cos(v))
+    ax.set_xlim(-2, 11)
+    ax.set_ylim(-2, 11)
+    ax.quiverkey(q, 0.5, 1, 1, 'N', labelpos='N')
+    ax.quiverkey(q, 1, 0.5, 1, 'E', labelpos='E')
+    ax.quiverkey(q, 0.5, 0, 1, 'S', labelpos='S')
+    ax.quiverkey(q, 0, 0.5, 1, 'W', labelpos='W')
+
+
 if __name__ == '__main__':
     import nose
     nose.runmodule()