Best practices for `unit` values?

[tylere]

The current raster spec does not give much guidance about the unit field, and inconsistency in the field may make datasets less interoperable.

As a concrete example, should a unit be meter or metre or meters or m or cm or km?

It would be good to describe a best practice for this field. For example:

• Use the International System of Units (SI) Here is a good overview
• Use SI base units or SI derived units
• Use the raster extension scale field rather than SI prefixes
• Use unit symbols rather than unit names

[m-mohr]

The datacube extension (and others, too, I think) use:

The unit of measurement for the data, preferably compliant to UDUNITS-2 units (singular).

Is this good enough? It's difficult to standardize here as people have so diverging needs.
This field will be migrated to STAC core metadata in 1.1 (raster 2.0) so is not that relevant for the raster extension, but for core.

[m-mohr]

Implemented in radiantearth/stac-spec#1254 through commit radiantearth/stac-spec@f35f5d8