[fitswcs] RADESYS = 'GAPPT'

[William Pence]

Steve,

The WCS section in the FITS Standard is not intended to include 
everything in the WCS Papers, so I don't think that the omission of the 
implementation details related to the GAPPT system should be considered 
a mistake.  As stated in the first paragraph of Section 8 of the FITS 
Standard:
"These WCS papers have been formally approved by the IAUFWG and 
therefore are incorporated by reference as an official part of this 
Standard.  The reader should refer to these papers for additional 
details and background information that cannot be included here."

-Bill

On 03/15/2011 07:56 PM, Steve Allen wrote:
> 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.
>
-- 
____________________________________________________________________
Dr. William Pence                       William.Pence at nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
Greenbelt MD 20771                      +1-301-286-1684 (fax)