Subject: Re: FITS Sorting Convention

From: leb at clark.net (Lee E. Brotzman)
Date: 1 Dec 1994 18:07:48 -0500

francois at SIMBAD.u-strasbg.fr writes:
>Just a few comments concerning the TSORTKEY convention proposed by OGIP:
>
>1) The proposed definition implies additional non-standard FITS requirements:
>   unique names, no possibility of names starting with the minus sign.
>   Since FITS headers are (fortunately!) to be read only by programs,
>   wouldn't it be so much simpler and less ambiguous to use only the 
>   TFIELD number, i.e. definitions like
>   TSORTKEY = '1,-2,12,-14'

I usually don't like to post "me too" messages, but I have to concur.  It is
"prettier" to use column names, however, since column names are not required,
but column numbers (TBCOL) are, then the only acceptable value would be the
numbers.  Plus, negative column numbers are unambiguous, whereas minus signs
before column names can be.

Also, as a programmer, having the numbers saves me code, as opposed to names
which require some type of table lookup.  So, all in all, using column numbers
is a win all the way around.
-- 
-- Lee E. Brotzman                    E-mail: leb at clark.net
-- Advanced Data Solutions            Phone : 301-776-0324
-- "Sometimes I think the surest sign that intelligent life exists elsewhere in
--  the Universe is that none of it has tried to contact us."  --- Calvin, 1990

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From: cgp at le.ac.uk (Dr C.G. Page)
Date: 2 Dec 1994 13:54:55 -0000

I appreciate the comments of Preben Grosbol that in theory it is possible to
construct FITS tables which have no column names, or ones which start with
minus-signs, or with duplicated names.  It seems to me, however, that such FITS
files are very rare and I think that everything should be done to discourage
their use. No one is required to adopt this convention for indicating how a
table is sorted, I don't think it matters that the TSORTKEY proposal will not
work on such pathological cases.  

-- 
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Clive Page,                         Internet: cgp at star.le.ac.uk
Dept of Physics & Astronomy,        
University of Leicester.