Merge pull request matplotlib#27044 from stevezhang1999/fix-quiver-key

Fix quiver key plot when angles='xy' and/or scale_units='xy'

Author: ksunden

lib/matplotlib/quiver.py

@@ -263,7 +263,7 @@ def __init__(self, Q, X, Y, U, label,
             The key label (e.g., length and units of the key).
         angle : float, default: 0
             The angle of the key arrow, in degrees anti-clockwise from the
-            x-axis.
+            horizontal axis.
         coordinates : {'axes', 'figure', 'data', 'inches'}, default: 'axes'
             Coordinate system and units for *X*, *Y*: 'axes' and 'figure' are
             normalized coordinate systems with (0, 0) in the lower left and
@@ -327,10 +327,8 @@ def _init(self):
                                    Umask=ma.nomask):
                 u = self.U * np.cos(np.radians(self.angle))
                 v = self.U * np.sin(np.radians(self.angle))
-                angle = (self.Q.angles if isinstance(self.Q.angles, str)
-                         else 'uv')
-                self.verts = self.Q._make_verts(
-                    np.array([u]), np.array([v]), angle)
+                self.verts = self.Q._make_verts([[0., 0.]],
+                                                np.array([u]), np.array([v]), 'uv')
             kwargs = self.Q.polykw
             kwargs.update(self.kw)
             self.vector = mcollections.PolyCollection(
@@ -521,7 +519,7 @@ def _init(self):
             # _make_verts sets self.scale if not already specified
             if (self._dpi_at_last_init != self.axes.figure.dpi
                     and self.scale is None):
-                self._make_verts(self.U, self.V, self.angles)
+                self._make_verts(self.XY, self.U, self.V, self.angles)
 
             self._dpi_at_last_init = self.axes.figure.dpi
 
@@ -537,7 +535,7 @@ def get_datalim(self, transData):
     @martist.allow_rasterization
     def draw(self, renderer):
         self._init()
-        verts = self._make_verts(self.U, self.V, self.angles)
+        verts = self._make_verts(self.XY, self.U, self.V, self.angles)
         self.set_verts(verts, closed=False)
         super().draw(renderer)
         self.stale = False
@@ -594,33 +592,38 @@ def _set_transform(self):
         self.set_transform(trans)
         return trans
 
-    def _angles_lengths(self, U, V, eps=1):
-        xy = self.axes.transData.transform(self.XY)
+    # Calculate angles and lengths for segment between (x, y), (x+u, y+v)
+    def _angles_lengths(self, XY, U, V, eps=1):
+        xy = self.axes.transData.transform(XY)
         uv = np.column_stack((U, V))
-        xyp = self.axes.transData.transform(self.XY + eps * uv)
+        xyp = self.axes.transData.transform(XY + eps * uv)
         dxy = xyp - xy
         angles = np.arctan2(dxy[:, 1], dxy[:, 0])
         lengths = np.hypot(*dxy.T) / eps
         return angles, lengths
 
-    def _make_verts(self, U, V, angles):
+    # XY is stacked [X, Y].
+    # See quiver() doc for meaning of X, Y, U, V, angles.
+    def _make_verts(self, XY, U, V, angles):
         uv = (U + V * 1j)
         str_angles = angles if isinstance(angles, str) else ''
         if str_angles == 'xy' and self.scale_units == 'xy':
             # Here eps is 1 so that if we get U, V by diffing
             # the X, Y arrays, the vectors will connect the
             # points, regardless of the axis scaling (including log).
-            angles, lengths = self._angles_lengths(U, V, eps=1)
+            angles, lengths = self._angles_lengths(XY, U, V, eps=1)
         elif str_angles == 'xy' or self.scale_units == 'xy':
             # 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.
             eps = np.abs(self.axes.dataLim.extents).max() * 0.001
-            angles, lengths = self._angles_lengths(U, V, eps=eps)
+            angles, lengths = self._angles_lengths(XY, U, V, eps=eps)
+
         if str_angles and self.scale_units == 'xy':
             a = lengths
         else:
             a = np.abs(uv)
+
         if self.scale is None:
             sn = max(10, math.sqrt(self.N))
             if self.Umask is not ma.nomask:
@@ -630,6 +633,7 @@ def _make_verts(self, U, V, angles):
             # crude auto-scaling
             # scale is typical arrow length as a multiple of the arrow width
             scale = 1.8 * amean * sn / self.span
+
         if self.scale_units is None:
             if self.scale is None:
                 self.scale = scale

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

@@ -267,6 +267,62 @@ def test_quiverkey_angles():
     assert len(qk.verts) == 1
 
 
+def test_quiverkey_angles_xy_aitoff():
+    # GH 26316 and GH 26748
+    # Test that only one arrow will be plotted with non-cartesian
+    # when angles='xy' and/or scale_units='xy'
+
+    # only for test purpose
+    # scale_units='xy' may not be a valid use case for non-cartesian
+    kwargs_list = [
+        {'angles': 'xy'},
+        {'angles': 'xy', 'scale_units': 'xy'},
+        {'scale_units': 'xy'}
+    ]
+
+    for kwargs_dict in kwargs_list:
+
+        x = np.linspace(-np.pi, np.pi, 11)
+        y = np.ones_like(x) * np.pi / 6
+        vx = np.zeros_like(x)
+        vy = np.ones_like(x)
+
+        fig = plt.figure()
+        ax = fig.add_subplot(projection='aitoff')
+        q = ax.quiver(x, y, vx, vy, **kwargs_dict)
+        qk = ax.quiverkey(q, 0, 0, 1, '1 units')
+
+        fig.canvas.draw()
+        assert len(qk.verts) == 1
+
+
+def test_quiverkey_angles_scale_units_cartesian():
+    # GH 26316
+    # Test that only one arrow will be plotted with normal cartesian
+    # when angles='xy' and/or scale_units='xy'
+
+    kwargs_list = [
+        {'angles': 'xy'},
+        {'angles': 'xy', 'scale_units': 'xy'},
+        {'scale_units': 'xy'}
+    ]
+
+    for kwargs_dict in kwargs_list:
+        X = [0, -1, 0]
+        Y = [0, -1, 0]
+        U = [1, -1, 1]
+        V = [1, -1, 0]
+
+        fig, ax = plt.subplots()
+        q = ax.quiver(X, Y, U, V, **kwargs_dict)
+        ax.quiverkey(q, X=0.3, Y=1.1, U=1,
+                     label='Quiver key, length = 1', labelpos='E')
+        qk = ax.quiverkey(q, 0, 0, 1, '1 units')
+
+        fig.canvas.draw()
+        assert len(qk.verts) == 1
+
+
 def test_quiver_setuvc_numbers():
     """Check that it is possible to set all arrow UVC to the same numbers"""