FIX: Update the extent when calling contour

This brings the bounds logic from contourf into contour
to properly update the extents of the plot.

lib/cartopy/mpl/geoaxes.py

@@ -1547,6 +1547,14 @@ def contour(self, *args, **kwargs):
         """
         result = matplotlib.axes.Axes.contour(self, *args, **kwargs)
 
+        # We need to compute the dataLim correctly for contours.
+        bboxes = [col.get_datalim(self.transData)
+                  for col in result.collections
+                  if col.get_paths()]
+        if bboxes:
+            extent = mtransforms.Bbox.union(bboxes)
+            self.dataLim.update_from_data_xy(extent.get_points())
+
         self.autoscale_view()
 
         # Re-cast the contour as a GeoContourSet.

lib/cartopy/tests/mpl/test_contour.py

@@ -61,3 +61,15 @@ def test_contour_linear_ring():
     ax.contourf(lons, lats, vals, np.arange(9), transform=ccrs.PlateCarree())
 
     plt.draw()
+
+
+def test_contour_update_bounds():
+    """Test that contour updates the extent"""
+    xs, ys = np.meshgrid(np.linspace(0, 360), np.linspace(-80, 80))
+    zs = ys**2
+    ax = plt.axes(projection=ccrs.Orthographic())
+    ax.contour(xs, ys, zs, transform=ccrs.PlateCarree())
+    # Force a draw, which is a smoke test to make sure contouring
+    # doesn't raise with an Orthographic projection
+    # GH issue 1673
+    plt.draw()