restructuring for polygon functions

cordex/crs.py

@@ -0,0 +1,37 @@
+from cartopy import crs as ccrs
+from .utils import get_grid_mapping_attrs
+from pyproj import CRS
+from xarray import Dataset
+
+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(attrs):
+    crs = crs_map.get(attrs["grid_mapping_name"])
+    kwargs = {kw: (attrs.get(v) or v) for kw, v in crs["kwargs"].items()}
+    return crs["crs"](**kwargs)
+
+
+def get_ccrs(obj):
+    if isinstance(obj, Dataset):
+        attrs = obj.cf["grid_mapping"].attrs
+    elif isinstance(obj, str):
+        attrs = get_grid_mapping_attrs(obj)
+    return _ccrs_from_cf(attrs)
+
+
+def get_crs(domain_id):
+    """creates a pyproj CRS instance from a CORDEX domain_id"""
+    # i go via from_cf to get the correct crs
+    attrs = get_grid_mapping_attrs(domain_id)
+    return CRS.from_cf(attrs)
+    # proj4 = f"+proj=ob_tran +o_proj=longlat +o_lon_p=0 +o_lat_p={dm.pollat} +lon_0={180+dm.pollon} +datum=WGS84 +no_defs +type=crs"