[fitswcs] Status of WCS negotiations

[Doug Mink]

Mark Calabretta wrote, in response to my message of Mon 1998/07/20
12:55:49 -0400,
>
>    1) Indicate what you're up to by adding a code to the CTYPEn.
>       For example, set them to RA---CFA, DEC--CFA.
> 
>    2) Define and publish an algorithm which implements "CFA".
> 
>    3) Encode the parameters used by "CFA" in header cards of the form
>       WCSiinnn (instead of COn_i).

This might be a good case for having multiple WCS's in a header: 
Allowing
for local creation of a more accurate projection CTYPE which could
coexist
peacefully with an almost equivalent standard projection.  In my case,
for example, I would have CTYPE1="RA---TAN", CTYPE2="DEC--TAN", ..., and
CTYPE1A="RA---CFA", CTYPE2A="DEC---CFA", ..., where the ellipses cover
the appropriate keywords for the given projection.


> However, rather than define a fairly special-purpose algorithm it would
> be better to define something which was more generally applicable so
> others could use it.  I believe the translation of the DSS projection
> I described in previous email would already satisfy your requirements.
> It includes terms up to x*(x^2 + y^2)^2 but you don't have to use them
> all.

I think that the DSS projection, other than--perhaps--its choice of
keywords, is a fine representation of what optical astrometrists want
in a projection.  My plate projection is mostly a simplification of
the DSS projection, leaving out the image to plate terms.

-Doug