Subject: Re: No ST-6 FITS images ?

From: bschlesinger at nssdca.gsfc.nasa.gov (BARRY M. SCHLESINGER)
Date: 31 Mar 1994 16:52 EDT

In article <94088.142150K3032E0 at ALIJKU11.BITNET>, Herbert Raab <K3032E0 at ALIJKU11.BITNET> writes...
>I once read a posting saying that FITS images written by the software of
>the ST-6 CCD camera do not fullfill the FITS standard.... 
> 
>What's wrong with the files written by the ST-6 software ?
> 
	
	Funny that this question should come up at this time.  They
use unsigned 16-bit integers, which, as we have been discussing here 
in the past month, FITS does not support. 

	While we are on the subject....  My suggestion for a new
extension type to hold unsigned integers in binary tables was not
intended as a permanent solution.  The idea is that such an extension
type would be used to hold the new forms during the process of
development.  Should the community consensus be to approve the new
data types, after approval they would be allowed in an extension with
type name BINTABLE. 

	About the calls for fast action....  I have added a paragraph on 
the procedures by which FITS evolves to the monthly basics and 
information posting.  (If it's gone at your site, it's available from
ftp://nssdca.gsfc.nasa.gov/fits/basics_info.txt)  Note that the 
process is deliberate.  This choice is no accident.  One of the
criticisms of FITS is that it has some awkward features.  Such
features arise largely because of the rule that no change can be
made that would invalidate a valid FITS file.  The presence of this
rule means that material can be cast into FITS format without fear
that at some time in the future a change in the rules will require
conversion of an extensive data library.  Providing users such
confidence is worth the cost of occasionally having to make constructs
somewhat more complicated than one would like.  However, because, as a
result, any extension to FITS will limit what can be done in the
future, it is essential that such additions be thought through very
carefully before endorsement, so that the future flexibility of FITS
not be unnecessarily compromised. 

				Barry Schlesinger
				NSSDC/NOST FITS Support Office