VOUnits next steps

There are no current plans to develop the VOUnits specification. However this page collects a few minor errata and suggestions for future work, which can be addressed if such plans do eventually emerge.

Below is a note of minor fixes already applied (by Norman)

* The list of 'deprecated by FITS' terms in Table 2 is slightly ambiguous. I've adjusted the text in the repository version of the standard, to clarify that these 'deprecations' derive from Table 4 in the FITS spec (which actually says they're deprecated by the IAU but doesn't take a position on the matter itself).

* The besselian and tropical years are not mentioned in that list of FITS-deprecated units -- they appeared by acclaim in the on-list discussions, and so ended up in the VOUnits list. I've removed them from the FITS column in the Unity library (which is what generates the document's Table 2); they're still recognised-but-deprecated in VOUnits.

* The units 'angstrom' and 'ohm' (as unit names) are correctly spelled with a lowercase initial letter, but in both cases their usual unit symbol is a non-ASCII character, so that their all-ASCII version here must be a word. Following the lead of the FITS and CDS standards, and of SI unit-symbols derived from surnames, and disagreeing with the OGIP standard, we have preferred the initial-capital symbol in VOUnits (thus `Angstrom' as the unit symbol, rather than `angstrom').

See volute commit for the document, and unity commit for the library.

-- NormanGray - 2014-10-27

Three further minor things:

* Arnold Rots has mentioned that the VOUnits document says that 'yr' is the FITS-preferred unit for year, but that it should instead be 'a'. See Table 34 of the FITS paper.

* It might be worth a refresh of this document in any case, since some of the URIs are wrong (it refers to Unity at bitbucket, and includes references to 'volute' at Google Code; if there were a move to adjust these, I (Norman) would need to think about identifying someplace to share the Unity source code repository, and create an issues list).

* The VOUnits document says 'An empty unit string positively indicates that the corresponding quantity is dimensionless. Since an empty string does not conform to the grammars below, this also must be checked for before unit-parsing starts.' It might be worth adding a special case of 'empty string' to the VOUnits grammar.

The first two could be dealt with as a pair of errata. The third would need a minor version bump.

-- NormanGray - 2021-07-01

I wonder if the document would gain in readibility by splitting the historical sections (appendix A & B) and providing them separately - they are a bit confusing when searching the doc to quickly find how to… plus, some examples with increasing complexity would help.

-- <a class=StephaneErard - 2023-06-04"/>