IVOA Units standard

[Norman Gray]

Greetings, all.

[cc-ed to semantics at ivoa and apps at ivoa for information -- I suggest discussion remain on interop at ivoa]

I'd like to encourage people to look at the wiki page covering the proposed "VOUnits" standard:

    http://www.ivoa.net/cgi-bin/twiki/bin/view/IVOA/DiscussionOnVOUnits

The goal of this effort is to create a specification of the allowed or recommended syntax for units, which can be referred to in turn from future IVOA standards.

It's slightly surprising that the IVOA has never quite got around to creating such a specification in the past (perhaps memories of the protracted 'quantities' discussions scared everyone off).

A few observations:

  * The question covers both the syntax for unit specifications, and the set of allowed or recommended units.

  * Some 'standards' already exist here.  The FITS standard is reasonably well known (and flexible), and the 'CDS' syntax is the one referred to in the VOTable standard.  Both of these are referred to in the VOUnits work.

  * The three existing syntaxes being examined are the FITS standard's units specification (disambiguated), the OGIP memo's specification, and a CDS specification.  See the URL below for links.

  * This is not expected to be particularly controversial.  We expect that the outcome will simply be to codify existing practice as much as possible.

The standardisation effort is accompanied by a parsing library <http://www.astro.gla.ac.uk/users/norman/ivoa/unity/>.  This is intended to be useful for those who wish to parse units (in Java or C), but also to act as a reference implementation and collection of test cases, thus verifying that the proposed syntaxes are in fact implementable and unambiguous.

Best wishes,

Norman


-- 
Norman Gray  :  http://nxg.me.uk
SUPA School of Physics and Astronomy, University of Glasgow, UK