[fitswcs] TAN+poly & astrometric discussions in WCS paper-2

[Doug Mink]

Peter Bunclark wrote:
> 
> Don, you keep using the string _interchange_ - good try, but FITS is
> just so phenomenally successful it is in fact used for far more than
> interchange; so much so that producers of reduction packages incorporating
> astrometry (I'm thinking of IRAF and STARLINK in particular) are waiting
> for this !"$%^&*() WCS to finalise before they'll cut yet more code;
> and FITS is becoming a data-reduction normal format, and most folk
> will use either packages or things like wcslib building blocks, so my
> point is, doing a lsq fit in ARC and transforming to TAN via an analytical
> patch to the polynomial terms is in practice several orders of magnitude
> harder than working in a coordinate system that appears in the FITS
> standard.

I agree with Pete here.  It is not that hard to either specify or implement
procedures for dealing with polynomials attached to many of the FITS
projections, and I prefer to use the numbers which were fit rather than
some transformation of them.  That's why I support the DSS WCS directly
in my package.

-Doug Mink