Little data models

[David Berry]

Martin,

Making standards is a slow business, but I think we made some serious
progress at Strasbourg.

> My first proposed data model will be for World Coordinates as this is my
> immediate urgent requirement.  I have seen hints that such a model exists but I
> can't find it, so if it does, let me know where it is!

I think I can safely say that no decisions have yet been made regarding
WCS in the DM group, but there has been some discussion. Relevant input
that I know of is:

1) the Space-Time-Coordinates schema produced by Arnold Rots (which has, I
think, been widely accepted throughout the IVOA, old-hands correct me if I
am wrong). Documented at

http://www.ivoa.net/internal/IVOA/IVOARegWp03/STCdoc.pdf

This gives a standard for describing all sorts of different coordinate
systems, but does not describe how to transform positions from one
coordinate system to another (e.g. from pixel coords to RA,Dec)

2) Transformations between coordinate systems is one of the issues
discussed in the [TRANSFORM] thread in the DM forum message archive.
There is also a suggestion for how arbitrary complex transformations could
be described in

http://www.ivoa.net/internal/IVOA/IVOADMTransformsWP/VOMapping.sxw

3) I gave a presentation at the Cambridge IVOA meeting in May on "A
toolkit approach to wcs" which you can see at

http://axp0.ast.man.ac.uk/~dsb/ast/IVOA_WCS_talk.html

But to re-iterate, no decision have been made.

I think what-ever WCS data model is finally adopted, FITS-WCS (in some
form) will *have* to be a valid instantiation of the model. This leaves
open the question of whether the WCS DM should be sufficiently general to
allow other more flexible instantiations as well.

David