API Design: Specifying Unit conversion for fields

[VeckoTheGecko]

In v3 we used fieldtype and the mesh (flat or spherical) to determine the UnitConverter object that is associated with a field.

It would be good to reconsider how this is done in the overall v4 API (or, at least, in terms of naming). This will become clearer further in v4 development

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Should we be concerned with the naming of

UWind.units = parcels.tools.converters.GeographicPolar()
VWind.units = parcels.tools.converters.Geographic()

? Previously it might have been easier to identify that VWind would be of field type V, whereas now its probably not as clear to the user that it needs a Geographic converter and not a GeographicPolar converter. Perhaps this would just be something to keep an eye on moving forward, that we can revisit the naming/how to specify these unit converters.

Originally posted by @VeckoTheGecko in #1942 (review)

[fluidnumerics-joe]

FWIW, at the moment, I'm using an attribute in an xarray.DataArray or uxarray.UxDataArray for the mesh_type (formerly the mesh argument for the Field.__init__) and the variable name. However, I'm considering reverting back to having the mesh_type (changing the name from mesh) as an argument to Field.__init__, rather than having it come in via a *DataArray attribute.

[VeckoTheGecko]

Unit conversion was removed in #2459 , and how is handled directly in either the (vector)interp or user kernels. The mesh argument in future will be determined automatically by the higher level APIs by looking at dataset attrs.