On Fri 2004-07-09T09:50:23 -0400, Arnold Rots hath writ:
It would have been convenient to have a single keyword that specifies
the spatial reference frame in use, and that could say 'FK4', 'ICRS',
'HCI', 'MAG', 'HCD', etc.

Then it would also be easy to add planetocentric coordinates, and we
could allow generic CTYPEs like X, Y, Z, LONG, LAT, etc.

Until such time as a fully machine-readable instance of such coordinates
is developed WCS currently provides enough string-valued keywords to
permit rather complete text-based documentation of the axes.

WCSNAMEa serves to name the overall coordinate system, and it might
be adapted to permit conventional values as above.

CTYPEia is being constrained to a 4-3 form for non-linear coordinates,
but with WCS III this is loosened by adding the CNAMEia keywords.

--
Steve Allen UCO/Lick Observatory Santa Cruz, CA 95064
Voice: +1 831 459 3046 http://www.ucolick.org/~sla
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