[fitswcs] Polarization codes

[Doug Tody]

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.

Someone (Mark I think) said earlier that it made sense to represent
the spatial, spectral, and polarization measurements as image axes,
since these represent fundamental physical measurements and can have
multiple values for a single dataset, and I think I agree.  That would
give us images of up to 4-D for a spectral data cube with polarization.
In general any of these "axes" might be degenerate, with a single
value.  The only fundamental physical measurement axis missing is the
time axis.  While not currently addressed by FITS, VO includes this.

	- Doug


On Thu, 13 Mar 2008, Steve Allen wrote:

> On Thu 2008-03-13T17:19:07 +0000, Paddy Leahy hath writ:
> > Hi Mark et al  (is anyone else reading these posts?)
> 
> As with Arnold, yes, but Lick only has one instrument designed to
> measure polarization, and my radio days were 25 years ago.
> 
> At the current stage of FITS evolution I find myself questioning the
> creation of any new conventional axis notions for PHDU and IMAGE data
> parallelepipeds.  Unless there is almost uniform agreement on the
> utility of such things it seems to me that it may be better to move
> such data into BINTABLE columns.  In that case each application can
> engineer its own set of descriptions without entangling the whole of
> the FITS community.  This may be a break with tradition for certain
> types of data, but it seems to be used well by the high energy
> community with their visualization and analysis tools.
> 
> --
> Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
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