Update regridder.grid property to ensure cf compliant coordinates

tests/test_regrid.py

@@ -1261,6 +1261,21 @@ def test_grid(self):
         ):
             ds_multi.regridder.grid  # noqa: B018
 
+    def test_grid_adds_cf_attributes_to_non_cf_compliant_coords(self):
+        ds = fixtures.generate_dataset(
+            decode_times=True, cf_compliant=False, has_bounds=True
+        )
+        # Remove "axis" and "standard_name" attributes.
+        ds["lat"].attrs = {"units": "degrees_east"}
+        ds["lon"].attrs = {"units": "degrees_north"}
+
+        grid = ds.regridder.grid
+
+        assert grid["lat"].attrs["axis"] == "Y"
+        assert grid["lat"].attrs["standard_name"] == "latitude"
+        assert grid["lon"].attrs["axis"] == "X"
+        assert grid["lon"].attrs["standard_name"] == "longitude"
+
     def test_grid_raises_error_when_dataset_has_multiple_dims_for_an_axis(self):
         ds_bounds = fixtures.generate_dataset(
             decode_times=True, cf_compliant=True, has_bounds=True

xcdat/regridder/accessor.py

@@ -4,7 +4,7 @@
 
 import xarray as xr
 
-from xcdat.axis import CFAxisKey, get_dim_coords
+from xcdat.axis import CF_ATTR_MAP, CFAxisKey, get_dim_coords
 from xcdat.regridder import regrid2, xesmf, xgcm
 from xcdat.regridder.grid import _validate_grid_has_single_axis_dim
 
@@ -109,13 +109,47 @@ def _get_axis_data(
 
         _validate_grid_has_single_axis_dim(name, coord_var)
 
+        coord_var = self._ensure_cf_compliance(coord_var, name)  # type: ignore
+
         try:
             bounds_var = self._ds.bounds.get_bounds(name, coord_var.name)
         except KeyError:
             bounds_var = None
 
         return coord_var, bounds_var
 
+    def _ensure_cf_compliance(
+        self, coord_var: xr.DataArray, name: CFAxisKey
+    ) -> xr.DataArray:
+        """Ensure that the coordinate variable is CF-compliant.
+
+        This function adds the "axis" and "standard_name" attributes to the
+        coordinates if they are not already present. Coordinates must be
+        CF-compliant in order for xESMF to interpret them using CF-xarray.
+
+        Parameters
+        ----------
+        coords : xr.DataArray
+            Coordinates to make CF compliant.
+        name : CFAxisKey
+            Name of the axis.
+
+        Returns
+        -------
+        xr.DataArray
+            CF compliant coordinates.
+        """
+        coord_var_new = coord_var.copy()
+        cf_attrs = CF_ATTR_MAP[name]
+
+        if "axis" not in coord_var_new.attrs:
+            coord_var_new.attrs["axis"] = cf_attrs["axis"]
+
+        if "standard_name" not in coord_var_new.attrs:
+            coord_var_new.attrs["standard_name"] = cf_attrs["coordinate"]
+
+        return coord_var_new
+
     def horizontal(
         self,
         data_var: str,