[AstroPy] FITS files and column descriptions

[Perry Greenfield]

On Nov 11, 2013, at 1:31 PM, Yannick Roehlly wrote:

> Le Mon, 11 Nov 2013 08:51:05 -0500,
> Perry Greenfield <stsci.perry at gmail.com> a écrit :
> 
>> What TOPCAT is doing is in no way part of the FITS standard.
> 
> Hi Perry,
> 
> As far as I understand, even the TCOMM keyword is not part of the FITS
> standard and they're is nothing in it to store column descriptions.
> Right?

Yes, I believe so. That is to say, nothing prevents you from using such keywords, but the standard doesn't give them any special meaning with regard to columns that anyone else is forced to recognize.

At least as keywords, they are more easily accessible from standard FITS readers (that don't need to do anything special to access them, unlike the meta data that is put into the primary HDU.

Also, I understand the reason they did that. It's there for those willing to go to the trouble to extract it. We are doing similar things for HST and JWST WCS information. But we don't assume that all other FITS readers must be able to access it. It's mainly for our software to use.

Perry