VEP-017: refframe#geo_app

[Francois Ochsenbein]

Hello Markus, Sebastien, Baptiste, everybody,

Just a few words about the "geo_app" value of the COOSYS keyword in VOTable,
introduced a quarter of a century ago.

The geocentric apparent position used to be the reference for the
ephemerides of the
solar system bodies for decades ; this frame has its origin at the
geocenter, and its axes coincide with the Earth orientation at the
epoch of the ephemeris. It might therefore be classified as
"equatorial", with refposition="geocenter", and its equinox value
identical to the epoch. However the "EQUATORIAL" term at
http://www.ivoa.net/rdf/refframe has the annotation : "Only use for
old, pre-FK4 equatorial coordinates", which can't be applied to the
apparent positions listed in the ephemerides of the last quarter of
the last century...

And thank you for the archeological researches :-)

Cheers,
François Ochsenbein