[fitswcs] Polarization codes

[Paddy Leahy]

On Thu, 13 Mar 2008, Doug Tody wrote:

> Hi All -
>
> I am sure there are plenty of other lurkers following this discussion,
> including myself.
>
> We are currently having a similar discussion within VO, in connection
> with the new version of the VO image access interface, which will
> support cube or N-D data including spectral and time cubes, and
> polarization.  We want this to be as compatible as possible with FITS.
> FITS pretty much addresses this already, at least for spectral data
> and polarization, but not I think for time cubes.
                                         ^^^^^^^^^^

A Google search indicates active work on this...    ;)

The point of my original post is that the current FITS WCS definition does 
not address the polarization case in enough generality.

Simple example: A common move in polarimetry is to convert (I,Q,U) 
triplets into (Angle, Fractional polarization, I) triplets which are 
easier to interpret (e.g. they map nicely to an HSV display). This 
conversion may not be trivial if you correct the polarized amplitude for 
noise bias.  But there is no standardised way of saving the latter triplet 
(even one layer at a time) in a FITS file...I mean: a way that allows 
programs to correctly interpret the file without the user having to look 
at the header. Hopefully the VO does better...if so, FITS should go with 
the VO convention.

regards,
 		Paddy