[fitswcs] Exhortation

[William Pence]

Don Wells wrote:

> My understanding is that the (ICRS-FK5) reference frame problem is
> well-understood by the pundits, and that we can expect that they
> (e.g. Pat Wallace) will supply the rest of us (e.g. Bill Pence) with
> code which we can incorporate in our applications to fix up CRVALi in
> archival data which is referred to FK4/FK5/etc. I have heard that
> there is already a new GSC which incorporates the (ICRS-FK5) change in
> the star coordinates, and that Dave Monet is expected to deliver a new
> version of his gigantic star catalog referred to the ICRS frame
> 'real-soon-now', so we can expect that future astronomy data
> processing will be referred to ICRS automatically. Obviously we need
> to agree on FITS conventions to indicate the reference frames for our
> imagery; this is a FITS notation issue which the G&C paper addresses
> in great detail (thanks, Pat!).

The preferred development path for new WCS algorithms, as far as I am
concerned, would be for them to be incorporated into Doug Mink's
wcstools library first, which then in turn will be incorporated into
CFITSIO.  Doug and I are currently collaborating on a little project to
add an interface to his wcstools routines into my CFITSIO FITS file
reader and writer.  Currently we plan to add 3 new routines to CFITSIO
that would perform the following WCS-related functions.

routine_A:  initialize an internal C structure that contains all the
necessary WCS parameters to compute WCS transformations for the
currently opened FITS image or table.

routine_B:  given an input pair of X and Y plate coordinates, return the
corresponding world coordinate (using the structure that was created by
routine_A).

routine_C:  given an input world coordinate, return the corresponding
plate X,Y coordinate (again using the structure that was created by
routine_A).

With this approach, I can treat the wcstools library as a black box, and
just distribute the latest version along with CFITSIO. (and I don't have
to deal with or understand the details of the WCS algorithms :-). 

-Bill