Improves error when axis is missing/incorrect attributes

tests/test_regrid.py

@@ -157,6 +157,23 @@ def setup(self):
             }
         )
 
+    def test_missing_dimension(self):
+        ds = fixtures.generate_dataset(
+            decode_times=True, cf_compliant=False, has_bounds=True
+        )
+
+        del ds.lat.attrs["axis"]
+
+        output_grid = grid.create_gaussian_grid(32)
+
+        regridder = regrid2.Regrid2Regridder(ds, output_grid)
+
+        with pytest.raises(
+            RuntimeError,
+            match="Could not find axis 'lat', ensure 'lat' exists and the attributes are correct.",
+        ):
+            regridder.horizontal("ts", ds)
+
     @pytest.mark.filterwarnings("ignore:.*invalid value.*divide.*:RuntimeWarning")
     def test_output_bounds(self):
         ds = fixtures.generate_dataset(

xcdat/regridder/regrid2.py

@@ -172,7 +172,13 @@ def _output_axis_sizes(self, da: xr.DataArray) -> Dict[str, int]:
         axis_name_map = {y[0]: x for x, y in da.cf.axes.items()}
 
         for standard_name in da.sizes.keys():
-            axis_name = axis_name_map[standard_name]
+            try:
+                axis_name = axis_name_map[standard_name]
+            except KeyError:
+                raise RuntimeError(
+                    f"Could not find axis {standard_name!r}, ensure {standard_name!r} "
+                    "exists and the attributes are correct."
+                )
 
             if standard_name in self._output_grid:
                 output_sizes[axis_name] = self._output_grid.sizes[standard_name]