added albers_conical_equal_area projection (#1344)

* added albers_conical_equal_area projection

* add extra blank lines around albers code

* two lines of white space (again)

src/metpy/plots/mapping.py

@@ -14,6 +14,7 @@
 class CFProjection(object):
     """Handle parsing CF projection metadata."""
 
+    # mapping from Cartopy to CF vocabulary
     _default_attr_mapping = [('false_easting', 'false_easting'),
                              ('false_northing', 'false_northing'),
                              ('central_latitude', 'latitude_of_projection_origin'),
@@ -124,6 +125,20 @@ def make_lcc(attrs_dict, globe):
     return ccrs.LambertConformal(globe=globe, **kwargs)
 
 
+@CFProjection.register('albers_conical_equal_area')
+def make_aea(attrs_dict, globe):
+    """Handle Albers Equal Area."""
+    attr_mapping = [('central_longitude', 'longitude_of_central_meridian'),
+                    ('standard_parallels', 'standard_parallel')]
+    kwargs = CFProjection.build_projection_kwargs(attrs_dict, attr_mapping)
+    if 'standard_parallels' in kwargs:
+        try:
+            len(kwargs['standard_parallels'])
+        except TypeError:
+            kwargs['standard_parallels'] = [kwargs['standard_parallels']]
+    return ccrs.AlbersEqualArea(globe=globe, **kwargs)
+
+
 @CFProjection.register('latitude_longitude')
 def make_latlon(attrs_dict, globe):
     """Handle plain latitude/longitude mapping."""

tests/plots/test_mapping.py

@@ -66,6 +66,34 @@ def test_globe_spheroid():
     assert globe_params['a'] == 6367000
     assert globe_params['b'] == 6360000
 
+
+def test_aea():
+    """Test handling albers equal area projection."""
+    attrs = {'grid_mapping_name': 'albers_conical_equal_area', 'earth_radius': 6367000,
+             'standard_parallel': [20, 50]}
+    proj = CFProjection(attrs)
+
+    crs = proj.to_cartopy()
+    assert isinstance(crs, ccrs.AlbersEqualArea)
+    assert crs.proj4_params['lat_1'] == 20
+    assert crs.proj4_params['lat_2'] == 50
+    assert crs.globe.to_proj4_params()['ellps'] == 'sphere'
+
+
+def test_aea_minimal():
+    """Test handling albers equal area projection with minimal attributes."""
+    attrs = {'grid_mapping_name': 'albers_conical_equal_area'}
+    crs = CFProjection(attrs).to_cartopy()
+    assert isinstance(crs, ccrs.AlbersEqualArea)
+
+
+def test_aea_single_std_parallel():
+    """Test albers equal area with one standard parallel."""
+    attrs = {'grid_mapping_name': 'albers_conical_equal_area', 'standard_parallel': 25}
+    crs = CFProjection(attrs).to_cartopy()
+    assert isinstance(crs, ccrs.AlbersEqualArea)
+    assert crs.proj4_params['lat_1'] == 20
+
 
 def test_lcc():
     """Test handling lambert conformal conic projection."""