Rename default `UnitConverter` to something more specific (e.g. `Unity()`)

[erikvansebille]

Reading through the unit converter guide in #2409, I realise that while Geographic and GeographicPolar are sensible names for UnitConverters, the default one (which does not do any conversion), is called UnitConverter.

Parcels/src/parcels/_core/converters.py

Lines 30 to 40 in 8480d1b

	class UnitConverter:
	"""Interface class for spatial unit conversion during field sampling that performs no conversion."""
	source_unit: str | None = None
	target_unit: str | None = None
	def to_target(self, value, z, y, x):
	return value
	def to_source(self, value, z, y, x):
	return value

That name may be confusing. Perhaps better to call it NoConversion? Or does anyone have a better name?

[VeckoTheGecko]

Personally I don't find it confusing

[erikvansebille]

I guess my confusion arises from the two meanings of the word "unit", which collide here. The classes in converters.py are meant to convert physical units; but the UnitConverter converts these units by unity (i.e. a factor 1.0).

The UnitConverter class can therefore be considered a pars pro toto; it signals both the suite of classes in the converters.py file and the function of that specific converter.

One option would be to call the suite of classes Converters in e.g. the tutorials and docstrings, but I don't think this solves the fundamental double meaning of the word "unit". So I do think it is confusing and propose we rename it.

If NoConversion() is not a good name, perhaps Unity()?

[reint-fischer]

I have also found the name UnitConverter confusing, and like Unity(), as it matches the other converters which are called Geographic() rather than GeographicConverter() or GeographicConversion()

[reint-fischer]

Thinking a bit more about the guide, I think it would be clearest if UnitConverter is still the base class, but Unity() is the default subclass. That way all objects are unitconverters, and a specific subclass must be defined for each Field. Would that make sense?

[erikvansebille]

Fixed in #2412