Subject: minus signs in Fits keywords

From: stoll at ocf.berkeley.edu (Cliff Stoll)
Date: 15 Jul 92 04:01:03 GMT

The Fits standard originally aimed at Fortran Namelist compatabilty
with header file keywords.  I don't think anyone's using
Fortran namelist utilities to read Fits header files, but it's
still an admirable goal.  It's also useful to map fits keywords 
directly onto program variables.

As written, however, Fits permits (and encourages) embedded minus
signs in keywords, for instance, MAX-RA.

Such keywords are incompatible with namelist reading and cannot
be mapped onto program variables in most languages.

This problem's been around for a while, but I trip over it every
couple years.  

-Cliff Stoll      stoll at ocf.berkeley.edu

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From: thompson at stars.gsfc.nasa.gov (William Thompson, code 682.1, x2040)
Date: 15 Jul 92 20:57:00 GMT

In article <1407tvINNje9 at agate.berkeley.edu>, stoll at ocf.berkeley.edu (Cliff Stoll) writes...
>-Cliff Stoll      stoll at ocf.berkeley.edu

For similar reasons, I'm recommending to the SOHO project that all keywords not
use embedded minus sign characters, but use underscores instead.

Bill Thompson

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From: bschlesinger at nssdca.gsfc.nasa.gov (Barry Schlesinger)
Date: 16 Jul 92 21:33:00 GMT

In article <15JUL199216574340 at stars.gsfc.nasa.gov>,
thompson at stars.gsfc.nasa.gov (William Thompson, code 682.1, x2040)
writes... 
>>signs in keywords, for instance, MAX-RA.

In FITS Paper I (A&A 1981, 44,363) the reserved and recommended
DATE-OBS keyword uses the hyphen (ASCII hexadecimal 2D).  Because, "we
are not permitted to alter the basic format in such a way as to make
existing FITS tapes invalid" (Paper III, A&A 1988, 73, p. 360, section
4) and the hyphen appears on many FITS data sets that use Paper I as a
model, its use cannot be forbidden now. 

I wouldn't say that future use is necessarily being encouraged.  A
straw in the wind is the ASCII Tables paper (A&A 1988 73,359)
recommendation that only letters (upper case) numbers, and underscore
be used for values of the TTYPEn keywords. 

>use embedded minus sign characters, but use underscores instead.

I would endorse this approach for user-defined keywords.

				Barry Schlesinger
				FITS Support Office