[fitswcs] RADESYS = 'GAPPT'

[Steve Allen]

Whilst implementing some new WCS writing code I am reviewing the
published version of the standard.  I find to my dismay that one
tidbit about RADESYS = 'GAPPT' is not in the standard.

Section 3.1 of FITS WCS Paper 2 says

    Geocentric apparent equatorial and ecliptic coordinates (GAPPT)
    require the epoch of the equator and equinox of date.  This will
    be taken as the time of observation rather than EQUINOXa

I cannot find anything in the published standard which points out
that the interpretation of GAPPT depends upon DATE-OBS or MJD-OBS.

--
Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
UCO/Lick Observatory--ISB   Natural Sciences II, Room 165    Lat  +36.99855
1156 High Street            Voice: +1 831 459 3046           Lng -122.06015
Santa Cruz, CA 95064        http://www.ucolick.org/~sla/     Hgt +250 m