added ccrs module

cordex/ccrs.py

@@ -0,0 +1,23 @@
+from cartopy import crs as ccrs
+
+crs_map = {
+    "rotated_latitude_longitude": {
+        "crs": ccrs.RotatedPole,
+        "kwargs": {
+            "pole_longitude": "grid_north_pole_longitude",
+            "pole_latitude": "grid_north_pole_latitude",
+            "central_rotated_longitude": 0.0,
+        },
+    }
+}
+
+
+def _ccrs_from_cf(mapping):
+    crs = crs_map.get(mapping.grid_mapping_name)
+    kwargs = {kw: (mapping.attrs.get(v) or v) for kw, v in crs["kwargs"].items()}
+    return crs["crs"](**kwargs)
+
+
+def get_ccrs(ds):
+    mapping = ds.cf["grid_mapping"]
+    return _ccrs_from_cf(mapping)