Added barbs method to GeoAxes.

lib/cartopy/mpl/geoaxes.py

@@ -1371,6 +1371,38 @@ def quiver(self, x, y, u, v, *args, **kwargs):
             u, v = self.projection.transform_vectors(t, x, y, u, v)
         return matplotlib.axes.Axes.quiver(self, x, y, u, v, *args, **kwargs)
 
+    def barbs(self, x, y, u, v, *args, **kwargs):
+        """
+        Plot a 2-D field of barbs.
+
+        See :func:`matplotlib.pyplot.barbs` for details on arguments
+        and keyword arguments.
+
+        .. note::
+
+           The vector components must be defined as grid eastward and
+           grid northward.
+
+        """
+        t = kwargs.get('transform', None)
+        if t is None:
+            t = self.projection
+        if isinstance(t, ccrs.CRS) and not isinstance(t, ccrs.Projection):
+            raise ValueError('invalid transform:'
+                             ' Spherical barbs are not supported - '
+                             ' consider using PlateCarree/RotatedPole.')
+        if isinstance(t, ccrs.Projection):
+            kwargs['transform'] = t._as_mpl_transform(self)
+        else:
+            kwargs['transform'] = t
+        if 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:
+                x, y = np.meshgrid(x, y)
+            u, v = self.projection.transform_vectors(t, x, y, u, v)
+        return matplotlib.axes.Axes.barbs(self, x, y, u, v, *args, **kwargs)
+
 
 def _trigger_patch_reclip(event):
     """

lib/cartopy/tests/mpl/test_mpl_integration.py

@@ -373,6 +373,28 @@ def test_quiver_rotated_pole():
     ax.quiver(x, y, u, v, mag, transform=rp)
 
 
+@ImageTesting(['barbs_plate_carree'])
+def test_barbs():
+    x = np.arange(-60, 45, 5)
+    y = np.arange(30, 75, 5)
+    x2d, y2d = np.meshgrid(x, y)
+    u = 40 * np.cos(np.deg2rad(y2d))
+    v = 40 * np.cos(2. * np.deg2rad(x2d))
+    mag = (u**2 + v**2)**.5
+    plot_extent = [-60, 40, 30, 70]
+    plt.figure(figsize=(6, 6))
+    # plot on native projection
+    ax = plt.subplot(211, projection=ccrs.PlateCarree())
+    ax.set_extent(plot_extent, crs=ccrs.PlateCarree())
+    ax.coastlines()
+    ax.barbs(x, y, u, v, length=4, linewidth=.25)
+    # plot on a different projection
+    ax = plt.subplot(212, projection=ccrs.NorthPolarStereo())
+    ax.set_extent(plot_extent, crs=ccrs.PlateCarree())
+    ax.coastlines()
+    ax.barbs(x, y, u, v, transform=ccrs.PlateCarree(), length=4, linewidth=.25)
+
+
 if __name__ == '__main__':
     import nose
     nose.runmodule(argv=['-s', '--with-doctest'], exit=False)