[fitsbits] Coordinate systems for solar image data (fwd)

[Steve Allen]

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
sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
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