Raise error when dimensions have no axis

Author: erikvansebille

src/parcels/_core/xgrid.py

@@ -55,6 +55,13 @@ def _transpose_xfield_data_to_tzyx(da: xr.DataArray, xgcm_grid: xgcm.Grid) -> xr
     """
     ax_dims = [(get_axis_from_dim_name(xgcm_grid.axes, dim), dim) for dim in da.dims]
 
+    for dim in ax_dims:
+        if dim[0] is None:
+            raise ValueError(
+                f'Dimension "{dim[1]}" has no axis attribute. '
+                f'HINT: You may want to add an {{"axis": A}} to your DataSet["{dim[1]}"], where A is one of "X", "Y", "Z" or "T"'
+            )
+
     if all(ax_dim[0] is None for ax_dim in ax_dims):
         # Assuming its a 1D constant field (hence has no axes)
         assert da.shape == (1, 1, 1, 1)

tests/test_xgrid.py

@@ -6,6 +6,7 @@
 import xarray as xr
 from numpy.testing import assert_allclose
 
+from parcels import Field
 from parcels._core.index_search import (
     LEFT_OUT_OF_BOUNDS,
     RIGHT_OUT_OF_BOUNDS,
@@ -134,6 +135,13 @@ def test_invalid_depth():
         XGrid.from_dataset(ds)
 
 
+def test_dim_without_axis():
+    ds = xr.Dataset({"z1d": (["depth"], [0])}, coords={"depth": [0]})
+    grid = XGrid.from_dataset(ds)
+    with pytest.raises(ValueError, match='Dimension "depth" has no axis attribute*'):
+        Field("z1d", ds["z1d"], grid)
+
+
 @pytest.mark.parametrize(
     "ds",
     [