spectral WCS in FITS

[Anita Richards]

>
> Anita Richards wrote:
> > Put another way, there is certainly the need for a standard, but that
> > should be independent of how it is implimented to describe FITS, VOTable,
> > ascii or whatever.
>
> In case of a data model it should indeed be independent of a particular
> implementation. But a data access layer without hooks to existing formats and
> protocols appears of little practical use. Therefore, it does make sense to
> keep in sync with the FITS community as far as data representation is
> concerned. If not we pay the price in terms of more complicated systems.
>

You are quite right - and maybe someone could give examples of actual
teleescope data in formats which could (not) be handled effectively - e.g.
Bob mentioned the large amount of single dish data which are simply ascii
tables of flux density/T_A (possibly at 2 pols, possibly with other
quantities) versus wavelength or equivalent e.g. chann. No (indeed not
necessarily linearly or even regularly related to wavelength).  However
unless I ahve misunderstood the debate, there is no question that the data
_can_ be handled, it is simply a question of how, and surely testing on
real data (or at least a detailed thought experiment) is the way to
proceed?

I agree with Markus that VOTable standards should recognise all standard
FITS but is the reverse necessary? i.e. if VOTable can do more than FITS,
is that a problem? So long as conversion in both directions is possible,
but possibly with loss of information.  What I am thinking of is:

FITS native spectrum > VOTable > FITS  all original information restored
                                       but some added info from VOTable
				       may be lost
VOTable native format > FITS some info may be lost

but in both cases, is the lost information material which FITS handling
tools can't cope with anyway? And if so, can't it be included as a VOTable
wrapper (and also accessible in human readable form so you know aht is not
accessble to your FITS tool but ou might like to know anyway?)

Or have I completely missed the point in whch case don't worry about
replying, I will shut up and listen.


thanks

A

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Dr. Anita M. S. Richards, AVO Astronomer
MERLIN/VLBI National Facility, University of Manchester,
Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, U.K.
tel +44 (0)1477 572683 (direct); 571321 (switchboard); 571618 (fax).