[fitsbits] programming interfaces for WCS defaults

[Steve Allen]

On Wed 2002-11-27T08:38:59 +0000, David Berry hath writ:
> > WCSNAMEA= 'My silly instance of the default world coordinate system'

> Presumably, if the author has decided to include a value for WCSNAMEA
> then the author at least must consider the associated default aleternate
> axis descriptions to be useful. Maybe it's simply a case of trusting the
> author to decide what is useful and what isn't.

In the contrived case above WCS version A corresponds to IRAF
"physical" or "logical" coordinates.  (Or is that "image" coordinates?
I can never remember which without hunting through a bunch of
documents of their local conventions.)

However in mentioning this I note yet another question that must be
answered by UIs and APIs.  Suppose that a UI/API offers the option of
choosing a WCS by the value of one of the WCSNAMEa cards, and suppose
also that the application uses established, pre-WCS meanings for
"physical", "logical", and/or "image" coordinates.  Then suppose that
a FITS file author includes WCSNAMEa cards with those values.

How does a UI/API unambiguously offer the option, and how does it
distinguish between the established, pre-WCS meaning of "logical" and
the WCSNAMEa version with a value "logical"?

This question could be construed as a need to establish some reserved
values for WCSNAMEa which have particular definitions, but that
could be difficult if existing usages are inconsistent.

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93