Repository: SciTools/cartopy

Issue:
1D quiver in non-PlateCarree projections
Using quiver with 1D arrays of `x`, `y`, `u`, `v` works just fine with `ccrs.PlateCarree()`, but raises a `ValueError` with any other projection:

``` python
ValueError: x, y, u and v arrays must be the same shape
```

Using `np.atleast_2d` fixes this, and the quiver docs do say: `Plot a 2-D field of arrows`.

However, I wonder if the `atleast2d` should be inside Cartopy, or if the 1D case should raise an error in PlateCarree too.

(See http://nbviewer.ipython.org/gist/ocefpaf/b2f79fe0f96fa1776b97 for a SSCCE.)



Discussion:

Resolving patch:
diff --git a/lib/cartopy/mpl/geoaxes.py b/lib/cartopy/mpl/geoaxes.py
--- a/lib/cartopy/mpl/geoaxes.py
+++ b/lib/cartopy/mpl/geoaxes.py
@@ -1423,7 +1423,7 @@ def pcolor(self, *args, **kwargs):
 
     def quiver(self, x, y, u, v, *args, **kwargs):
         """
-        Plot a 2-D field of arrows.
+        Plot a field of arrows.
 
         Extra Kwargs:
 
@@ -1487,7 +1487,7 @@ def quiver(self, x, y, u, v, *args, **kwargs):
         elif t != self.projection:
             # Transform the vectors if the projection is not the same as the
             # data transform.
-            if x.ndim == 1 and y.ndim == 1:
+            if (x.ndim == 1 and y.ndim == 1) and (x.shape != u.shape):
                 x, y = np.meshgrid(x, y)
             u, v = self.projection.transform_vectors(t, x, y, u, v)
         return matplotlib.axes.Axes.quiver(self, x, y, u, v, *args, **kwargs)


Test patch:
diff --git a/lib/cartopy/tests/mpl/test_quiver.py b/lib/cartopy/tests/mpl/test_quiver.py
new file mode 100644
--- /dev/null
+++ b/lib/cartopy/tests/mpl/test_quiver.py
@@ -0,0 +1,83 @@
+# (C) British Crown Copyright 2015 - 2016, Met Office
+#
+# This file is part of cartopy.
+#
+# cartopy is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the
+# Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# cartopy is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with cartopy.  If not, see <http://www.gnu.org/licenses/>.
+
+from __future__ import (absolute_import, division, print_function)
+
+import unittest
+try:
+    from unittest import mock
+except ImportError:
+    import mock
+
+from nose.tools import raises, assert_equal
+import numpy as np
+import matplotlib.pyplot as plt
+from matplotlib.testing.decorators import cleanup
+
+import cartopy.crs as ccrs
+
+
+# Note, other tests for quiver exist in test_mpl_integration.
+
+class TestQuiverShapes(unittest.TestCase):
+    def setUp(self):
+        self.x = np.linspace(-60, 42.5, 10)
+        self.y = np.linspace(30, 72.5, 7)
+        self.x2d, self.y2d = np.meshgrid(self.x, self.y)
+        self.u = np.cos(np.deg2rad(self.y2d))
+        self.v = np.cos(2. * np.deg2rad(self.x2d))
+        self.rp = ccrs.RotatedPole(pole_longitude=177.5, pole_latitude=37.5)
+        self.pc = ccrs.PlateCarree()
+        self.ax = plt.axes(projection=self.pc)
+
+    @cleanup
+    def test_quiver_transform_xyuv_1d(self):
+        with mock.patch('matplotlib.axes.Axes.quiver') as patch:
+            self.ax.quiver(self.x2d.ravel(), self.y2d.ravel(),
+                           self.u.ravel(), self.v.ravel(), transform=self.rp)
+        args, kwargs = patch.call_args
+        assert_equal(len(args), 5)
+        assert_equal(sorted(kwargs.keys()), [u'transform'])
+        shapes = [arg.shape for arg in args[1:]]
+        # Assert that all the shapes have been broadcast.
+        assert_equal(shapes, [(70, )] * 4)
+
+    @cleanup
+    def test_quiver_transform_xy_1d_uv_2d(self):
+        with mock.patch('matplotlib.axes.Axes.quiver') as patch:
+            self.ax.quiver(self.x, self.y, self.u, self.v, transform=self.rp)
+        args, kwargs = patch.call_args
+        assert_equal(len(args), 5)
+        assert_equal(sorted(kwargs.keys()), [u'transform'])
+        shapes = [arg.shape for arg in args[1:]]
+        # Assert that all the shapes have been broadcast.
+        assert_equal(shapes, [(7, 10)] * 4)
+
+    @raises(ValueError)
+    def test_quiver_transform_xy_2d_uv_1d(self):
+        self.ax.quiver(self.x2d, self.y2d,
+                       self.u.ravel(), self.v.ravel(), transform=self.rp)
+
+    @raises(ValueError)
+    def test_quiver_transform_inconsistent_shape(self):
+        self.ax.quiver(self.x, self.y,
+                       self.u.ravel(), self.v.ravel(), transform=self.rp)
+
+
+if __name__ == '__main__':
+    import nose
+    nose.runmodule(argv=['-s', '--with-doctest'], exit=False)