Add functionality for correct transforms in ax.annotate

lib/cartopy/mpl/geoaxes.py

@@ -1685,6 +1685,48 @@ def scatter(self, *args, **kwargs):
         self.autoscale_view()
         return result
 
+
+    @_add_transform
+    def annotate(self, text, xy, xytext=None, xycoords='data', textcoords=None,
+                     *args, **kwargs):
+        """
+        Add the "transform" keyword to :func:`~matplotlib.pyplot.annotate`.
+
+        Other Parameters
+        ----------------
+        transform
+            A :class:`~cartopy.crs.Projection`.
+
+        """
+        transform = kwargs.pop('transform', None)
+        is_transform_crs = isinstance(transform, ccrs.CRS)
+
+        # convert CRS to mpl transform for default 'data' setup
+        if is_transform_crs and xycoords=='data':
+            xycoords = transform._as_mpl_transform(self)
+
+        # textcoords = xycoords be default but complains if xytext is empty
+        if textcoords is None and xytext is not None:
+            textcoords = xycoords
+
+        # use transform if textcoords is data and xytext is provided
+        if is_transform_crs and xytext is not None and textcoords=='data':
+            textcoords = transform._as_mpl_transform(self)
+
+        # convert to mpl_transform if CRS passed to xycoords
+        if isinstance(xycoords, ccrs.CRS):
+            xycoords = xycoords._as_mpl_transform(self)
+
+        # convert to mpl_transform if CRS passed to textcoords
+        if isinstance(textcoords, ccrs.CRS):
+            textcoords = textcoords._as_mpl_transform(self)
+
+        result = super().annotate(text, xy, xytext, xycoords=xycoords, textcoords=textcoords,
+                                  *args, **kwargs)
+        self.autoscale_view()
+        return result
+
+
     @_add_transform
     def hexbin(self, x, y, *args, **kwargs):
         """

lib/cartopy/tests/mpl/test_mpl_integration.py

@@ -856,3 +856,130 @@ def test_streamplot():
     ax.streamplot(x, y, u, v, transform=ccrs.PlateCarree(),
                   density=(1.5, 2), color=mag, linewidth=2 * mag)
     return fig
+
+
+@pytest.mark.natural_earth
+@pytest.mark.mpl_image_compare(filename='annotate_mercator.png', style='mpl20',)
+def test_annotate_backwardscompat():
+    """ Work around for annotate to work from 
+    https://stackoverflow.com/questions/25416600/why-the-annotate-worked-unexpected-here-in-cartopy/25421922#25421922
+    - check that an mpl_transform is passed through without issue. 
+    """
+    fig = plt.figure(figsize=(10, 5))
+    ax = fig.add_subplot(1, 1, 1, projection=ccrs.Mercator())
+
+    ax.set_extent([65, 125, 5, 40])
+    ax.coastlines()
+    ax.plot(116.4, 39.95, 'ob', transform=ccrs.PlateCarree())
+
+    transform = ccrs.PlateCarree()._as_mpl_transform(ax)
+    ax.annotate('Beijing', xy=(116.4, 39.9), xycoords=transform,
+                ha='right', va='top')
+    ax.annotate('Delhi', xy=(113, 40.5), xytext=(77.23, 28.61),
+                arrowprops=dict(facecolor='gray',
+                                arrowstyle="simple",
+                                connectionstyle="arc3,rad=-0.2",
+                                alpha=0.5),
+                xycoords=transform,
+                ha='right', va='top')
+
+    return fig
+
+
+@pytest.mark.natural_earth
+@pytest.mark.mpl_image_compare(filename='annotate_mercator.png', style='mpl20',)
+def test_annotate_mercator():
+    """ Update `test_annotate_backwardscompat` to use ccrs.PlateCarree 
+        as xycoords argument
+    """
+    fig = plt.figure(figsize=(10, 5))
+    ax = fig.add_subplot(1, 1, 1, projection=ccrs.Mercator())
+
+    ax.set_extent([65, 125, 5, 40])
+    ax.coastlines()
+    ax.plot(116.4, 39.95, 'ob', transform=ccrs.PlateCarree())
+
+    transform = ccrs.PlateCarree()
+    ax.annotate('Beijing', xy=(116.4, 39.9), xycoords=transform,
+                ha='right', va='top')
+    ax.annotate('Delhi', xy=(113, 40.5), xytext=(77.23, 28.61),
+                arrowprops=dict(facecolor='gray',
+                                arrowstyle="simple",
+                                connectionstyle="arc3,rad=-0.2",
+                                alpha=0.5),
+                xycoords=transform,
+                ha='right', va='top')
+
+    return fig
+
+
+@pytest.mark.natural_earth
+@pytest.mark.mpl_image_compare(filename='annotate_robinson.png',style='mpl20',)
+def test_global_annotate():
+    """ test a variety of annotate options on robinson projection
+    """
+
+    fig = plt.figure(figsize=(10, 5))
+    ax = fig.add_subplot(1, 1, 1, projection=ccrs.Robinson())
+    ax.set_global()
+    ax.coastlines()
+    platecarree = ccrs.PlateCarree()
+
+    """Add annotation with xycoords as projection"""
+    ax.plot(-75, 10, 'o', transform=platecarree)
+    ax.annotate('point 1', (-75, 10), xycoords=platecarree)
+
+    """Add annotation with point and text via transform"""
+    ax.plot(-75, -20, 'o', transform=platecarree)
+    ax.annotate('point 2', (-75, -20), xytext=(75, -35),
+                transform=platecarree,
+                arrowprops=dict(facecolor='red', arrowstyle="-|>",
+                                  connectionstyle="arc3,rad=-0.2",),
+                                  )
+
+    """Add annotation with point via transform and text non transformed"""
+    ax.scatter(75, -20, transform=platecarree)
+    ax.annotate('offset text', (75, -20), xycoords=platecarree,
+                xytext=(5, 15), textcoords='offset points',
+                size=5, va="center", ha="center",
+                bbox=dict(boxstyle="round4", fc="w"),
+                arrowprops=dict(facecolor='red', arrowstyle="-|>",
+                                  connectionstyle="arc3,rad=-0.2",),
+                                  )
+    return fig
+
+
+@pytest.mark.natural_earth
+@pytest.mark.mpl_image_compare(filename='annotate_homolosine.png', style='mpl20',)
+def test_homolosine_annotate():
+    """ test a variety of annotate options on robinson projection
+    """
+
+    fig = plt.figure(figsize=(10, 5))
+    ax = fig.add_subplot(1, 1, 1, projection=ccrs.InterruptedGoodeHomolosine())
+    ax.set_global()
+    ax.coastlines()
+    platecarree = ccrs.PlateCarree()
+
+    """Add annotation with xycoords as projection"""
+    ax.plot(-75, 10, 'o', transform=platecarree)
+    ax.annotate('point 1', (-75, 10), xycoords=platecarree)
+
+    """Add annotation with point and text via transform"""
+    ax.plot(-75, -20, 'o', transform=platecarree)
+    ax.annotate('point 2', (-75, -20), xytext=(25, -35),
+                transform=platecarree,
+                arrowprops=dict(facecolor='red', arrowstyle="-|>",
+                                  connectionstyle="arc3,rad=-0.2",),
+                                  )
+
+    """Add annotation with point via transform and text non transformed"""
+    ax.scatter(75, -20, transform=platecarree)
+    ax.annotate('offset text', (75, -20), xycoords=platecarree,
+                xytext=(15, -15), textcoords='offset points',
+                size=5, va="center", ha="center",
+                bbox=dict(boxstyle="round4", fc="w"),
+                arrowprops=dict(facecolor='red', arrowstyle="-|>",
+                                  connectionstyle="arc3,rad=-0.2",),
+                                  )
+    return fig