[fitsbits] Spectral FITS -- encoding extraction area/continuum

[David Berry]

On Thu, 17 Feb 2005, Mark Calabretta wrote:

> It is recognized that WCS Paper IV will need to deal with something like
> this, e.g. to allow distortion functions to be described separately for
> each CCD in an image composed of a mosaic of CCDs.  However, no real
> thought has been given to it.
>
> >RAPi_j = 1.2345  / RA of Polygonal Aperture [deg]
> >DAPi_j = 2.3448  / RA of Polygonal Aperture [deg]
>
> I think this, or something similar to it, is probably about the best you
> could do for now.
>
> However, a general scheme for Paper IV would have to differ in a number
> of respects:
>
> * It could not be limited to two coordinate axes, and not just to RA &
>   Dec, so the "R" and "D" in R/DAPi_j would have to become integer
>   indices.

Support for N-dimensional polygons sounds hard! The IVOA STC model
restricts polygons to 2D.

David