WCS problems on Optical Telescopes.

[Doug Mink]

Peter Bunclark wrote:
> 
> WCS on Optical Telescopes.
> 
> WCS failed to mature into a standard at ADASS'97, and it seemed to me
> that despite optimism over the progress made, the consensus churned
> rather than converged.
...

> 6. I feel it would be more elegant to include a mapping which adds
> radial distortion onto a classical tangent plane, even though
> arc+radial probably gives about the same result.
...

I have a program, IMWCS (http://tdc-www.harvard.edu/software/wcstools),
which automatically fits a plane-tangent WCS to a FITS image, usually
an optical telescope image.  It has worked fine on single chip CCD
images, but the vagaries of CCD mosaic astrometry are causing me to
add a polynomial.  I proposed to Don Wells and Eric Griesen that a
tangent plane plus polynomial projection be added to Mark Calabretta's
WCSLIB, and they said go ahead and propose it.  I am going to add it to
my own software first, to make sure it works, then more formally propose
it to the keepers of the WCS (of which I am sort of a member).  Lindsay
Davis at NOAO is using a TAN plus polynomial projection to do astrometry
with the NOAO mosaic and agrees that this is a good idea.  I propose a
TPN projection similar to the ARC plus polynomial (ZPN?) projection in
the Calabretta library.  I think that there could be consensus in the
optical community about the importance of such a projection, and would
like to hear from others who might be interested, especially those who
weren't at ADASS.
-Doug Mink
 Telesecope Data Center
 Harvard-Smithsonian Center for Astrophysics
 Cambridge Massachusetts USA