Raise error when creating Field with dimensions without axis

[erikvansebille]

This PR raises an error when users create a Field based on a grid with dimensions without axis. I found on multiple occasions, that without this error, the assert just below breaks:

Parcels/src/parcels/_core/xgrid.py

Lines 65 to 67 in 419ce76

	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)

One example is the unit test added to this PR

Parcels/tests/test_xgrid.py

Lines 138 to 142 in 419ce76

	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)

Not sure though if this is the best place for this error message. Some other, previously passing tests, now fail.

@VeckoTheGecko, perhaps you could weigh in where this error would be most appropriate ?

[VeckoTheGecko]

Not sure though if this is the best place for this error message. Some other, previously passing tests, now fail.

@VeckoTheGecko, perhaps you could weigh in where this error would be most appropriate ?

I think it would be great to have in a dedicated function - I've pushed a patch baa16c7 . Thoughts?

[erikvansebille]

Yep, good solution, @VeckoTheGecko. I like this!

[VeckoTheGecko]

LGTM!