Using FieldSet.from_xarray_dataset with cgrid_tracer requires two step approach

[apatlpo]

Question

Question

I with to specify to build a fieldset from an xarray dataset.
Amongst the variables, there are tracer variables that I wish to sample.
I just realized that if I wish to benefit from "cgrid_tracer" for the tracers, this needs to be done after the creation of the Fieldset (which are set to "cgrid_velocity" otherwise).
It's easy to overlook this behavior (which differs from what goes on in methods such as from_nemo, from_croco, ...)
Could you please confirm, my understanding is correct ?

Supporting code

fieldset = FieldSet.from_xarray_dataset(
    ds,
    variables=variables,
    dimensions=dims,
    interp_method="cgrid_velocity",
    allow_time_extrapolation=True,
    gridindexingtype="mitgcm",
)

# tracer interp_method are all 'cgrid_velocity'

# fix tracer interpolations
for f in fieldset.get_fields():
    if f not in ["U", "V", "UV"]:
        f.interp_method = "cgrid_tracer"

[erikvansebille]

Thanks for reporting this, @apatlpo. You're right that FieldSet.from_xarray_dataset() doesn't automatically detect fields like from_nemo() and from_croco() do, so your solution seems a very good workaround to me!

Note that with the new Parcels v4, all input will be via xarray DataSets, so this workaround won't be necessary anymore