Setting Field units implicitly through the mesh-type

Advantage si that this would also work when users add diffusion fields later

Author: erikvansebille

src/parcels/_core/fieldset.py

@@ -243,8 +243,6 @@ def from_copernicusmarine(ds: xr.Dataset):
         if "U" in ds.data_vars and "V" in ds.data_vars:
             fields["U"] = Field("U", ds["U"], grid, XLinear)
             fields["V"] = Field("V", ds["V"], grid, XLinear)
-            fields["U"].units = GeographicPolar()
-            fields["V"].units = Geographic()
 
             if "W" in ds.data_vars:
                 ds["W"] -= ds[

tests/test_fieldset.py

@@ -6,7 +6,7 @@
 import pytest
 import xarray as xr
 
-from parcels import Field, ParticleFile, ParticleSet, VectorField, XGrid
+from parcels import Field, Geographic, GeographicPolar, ParticleFile, ParticleSet, VectorField, XGrid
 from parcels._core.fieldset import CalendarError, FieldSet, _datetime_to_msg
 from parcels._datasets.structured.circulation_models import datasets as datasets_circulation_models
 from parcels._datasets.structured.generic import T as T_structured
@@ -260,9 +260,11 @@ def test_fieldset_from_copernicusmarine(ds, caplog):
 
 
 @pytest.mark.parametrize("ds", _COPERNICUS_DATASETS)
-def test_grid_mesh_from_copernicusmarine(ds):
+def test_grid_mesh_units_from_copernicusmarine(ds):
     fieldset = FieldSet.from_copernicusmarine(ds)
     assert fieldset.U.grid._mesh == "spherical"
+    assert isinstance(fieldset.U.units, GeographicPolar)
+    assert isinstance(fieldset.V.units, Geographic)
 
 
 @pytest.mark.parametrize("ds", [datasets_circulation_models["ds_copernicusmarine"].copy()])