Merge pull request #1160 from QuLogic/mercator-threshold

Use both x/y limits to determine Mercator threshold.

lib/cartopy/crs.py

@@ -1013,7 +1013,8 @@ def __init__(self, central_longitude=0.0,
                                        np.array([min_latitude, max_latitude]))
         self._xlimits = tuple(limits[..., 0])
         self._ylimits = tuple(limits[..., 1])
-        self._threshold = np.diff(self.x_limits)[0] / 720
+        self._threshold = min(np.diff(self.x_limits)[0] / 720,
+                              np.diff(self.y_limits)[0] / 360)
 
     def __eq__(self, other):
         res = super(Mercator, self).__eq__(other)

lib/cartopy/tests/mpl/test_set_extent.py

@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2011 - 2017, Met Office
+# (C) British Crown Copyright 2011 - 2018, Met Office
 #
 # This file is part of cartopy.
 #
@@ -61,6 +61,26 @@ def test_extents():
                               )
 
 
+@cleanup
+def test_get_extent():
+    # tests that getting the extents of a map produces something reasonable.
+    uk = [-12.5, 4, 49, 60]
+    uk_crs = ccrs.PlateCarree()
+
+    ax = plt.axes(projection=ccrs.PlateCarree())
+    ax.set_extent(uk, crs=uk_crs)
+    assert_array_almost_equal(ax.get_extent(uk_crs), uk)
+
+    ax = plt.axes(projection=ccrs.Mercator())
+    ax.set_extent(uk, crs=uk_crs)
+    assert_array_almost_equal(ax.get_extent(uk_crs), uk)
+
+    ax = plt.axes(projection=ccrs.Mercator(min_latitude=uk[2],
+                                           max_latitude=uk[3]))
+    ax.set_extent(uk, crs=uk_crs)
+    assert_array_almost_equal(ax.get_extent(uk_crs), uk, decimal=1)
+
+
 @cleanup
 def test_domain_extents():
     # Setting the extent to global or the domain limits.