Subject: WCS for long-slit spectroscopy

From: "Malcolm J. Currie" <mjc at roe.ac.uk>
Date: Fri, 12 Jun 1998 16:12:41 +0100

Since ADASS the WCS debate has gone quiet on this newsgroup.  Dare one
ask what is the current state of play with the draft standard?

I'm trying to define sets FITS headers to specify the WCS for both
imaging and spectroscopic detectors at UKIRT.  Since there is no WCS
standard yet, I've adopted the widely used AIPS tangent plane for
imaging, with non-zero CROTAn to allow for a small detector
orientation with respect to cardinal points.

Defining keywords is not straightforward with spectroscopic data,
especially long-slit spectroscopy.  (For those not familiar with the
problem, long-slit datasets have sky co-ordinates at each slit position
in addition to the x-y pixels of the two-dimensional detector/data
array.)  For a single spectrum I could add dummy third and fourth
dimensions which specify the sky co-ordinates for that spectrum. 
However, I'm uncertain what is the best approach (i.e. one that many
FITS readers would be able to interpret) for long-slit data.  Therefore
I'd like to know please what schemes other people have devised or
recommend for such data. 

Thanks,

Malcolm Currie
UKATC