Subject: Re: FITS viewer / FITS file format

From: [email-masked] (BARRY M. SCHLESINGER)
Date: Wed, 28 Apr 1993 18:54:00 GMT

In article <[email-masked]>, [email-masked] (Ken R Pergrem) writes...
>Does anyone know if there is a FITS image viewer available for
>the Mac and/or PC? Is it ftpable from somewhere?
> 
Well, first of all, one talks of FITS reader, not FITS viewers. 

	FITS (Flexible Image Transport System) is a data format
designed to provide a means for convenient exchange of astronomical
data between installations whose standard internal formats and
hardware differ. A FITS file is composed of a sequence of Header Data
Units (HDUs). The header consists of keyword=value statements, which
describe the format and organization of the data in the HDU and may
also provide additional information, for example, about the instrument
or the history of the data.  The data follow, structured as the header
specifies. The data section of the HDU may contain a digital image,
but, except for the first, *it doesn't have to*.  Other possible formats
include tables and multidimensional matrices that are not images. The
first HDU must contain a multidimensional matrix or no data at all;
the data in subsequent HDUs, called extensions, may be of any type,
consistent with certain rules.  The "Image" in the name comes from the
original use of the format to transport digital images, but it's not
just for images any more. 

 	FITS is not principally a graphics format designed for the
transfer of pictures; it does not incorporate "FITS viewers", packages
for decoding the data into an image.  Users must develop or obtain
separate software to convert the data from the FITS file into a form
that can be readily displayed.

IMDISP 7.8, an interactive image processing program that runs on an
IBM PC computer and supports FITS input, is available via anonymous
ftp at ames.arc.nasa.gov [128.102.18.3] in a file called imdisp78.zip
in the pub/SPACE/SOFTWARE subdirectory and at hypatia.gsfc.nasa.gov in
the pub/software/imdisp subdirectory.  It is also available through
Simtel-20 [192.88.110.20] at PD1:<MSDOS.GRAPHICS>IMDISP78.ZIP. 

I do not know of any widely used and applicable FITS readers for Mac.

>Also, where can I find the specifications for the FITS image format?
> 

Information on FITS references appears in the monthly FITS basics and
information post to sci.astro.fits.  The contents are available by
anonymous ftp at nssdca.gsfc.nasa.gov, directory FITS, file
BASICS_INFO.TXT.  NSSDCA is a VAX; case should not be significant 

			Barry Schlesinger
			NSSDC/NOST FITS Support Office