[fitswcs] Polarization codes

[Doug Tody]

Hi Paddy -

On Thu, 13 Mar 2008, Paddy Leahy wrote:
> As you pointed out, polarization is one of the four fundamental parameters 
> (along with time, frequency & sky position) that are needed for a complete 
> description of astronomical observations. For each of the other three 
> (counting the recommendations on time in the draft FITS standard v.3), 
> FITS defines numerous alternative ways of recording equivalent 
> information, and it is routine to save data after transforming from one of 

You may have a point, for example we permit velocity for the spectral
axis and apparently could not live without it.  With these things
there is always a certain amount of art to adjust the standard to fit
the most important use-cases while still remaining reasonably simple.
It would be good to hear from some others on this; also on the issue
of support for the time coordinate.  Ideally we need to support all
four principal observational parameters reasonably well while allowing
any to be degenerate in a given dataset.  FITS does pretty well but
is lacking in a couple of areas.  As I said earlier, this is not just
an issue for FITS evolution, we have an near term need to figure out
what to do about this for VO - but many of the real experts in this
area are here in FITS-land.

    - Doug