[fitswcs] RADESYS = 'GAPPT'

[Rob Seaman]

On Mar 16, 2011, at 10:49 AM, Steve Allen wrote:

> In almost all cases the most precise WCS which can be written into the
> FITS file at the telescope will be to ascertain whether the telescope
> is on-target, and if so to use the catalog coordinates of the target.

"At the telescope" is broader than "raw from detector read-out".  Current major instruments are typically/always part of a larger data handling system that is responsible for other shenanigans such as deinterlacing multiple pixel streams, rotating or transposing the arrays, merging metadata from multiple sources, checksumming and compression, etc.  Some instruments have integrated mountain-top pipelines.

Which is all to say that another possibility is to ignore the telescope pointing and run the astrometry.net code from a postprocessing command.

For other instrumentation such as multi-object spectrographs, the notion of telescope pointing is quite a bit different.  What does it mean for a bench spectrograph to be "on-target"?

Rob