Subject: On using .fits as a file extension

From: hybl at umbc4.umbc.edu (Dr. Albert Hybl (UMAB-BIOPHYS))
Date: Wed, 1 Jul 1992 23:54:48 GMT

The extension '.fits' does not guaranty anything about the contents
of the file.  The contents of the file must be examined to validate
that it conforms with the FITS standard.  The extension is just
a lazy man's way to remember something.  I have seen the extensions:
'.f', '.F', '.for', '.ftn' and others used to identify F77 Fortran
source code.  I _store_ my FITS files with the extension '.fits.Z'
where the '.Z' indicates that the files are compressed.  I
don't think that I can present an 'image.fits.Z' file to IRAF.
Why not?  The '.Z' extension is more standard than '.fits'; I would
like to have the programs look for '.Z' and if the program finds that
the file isn't a standard FITS file after uncompressing, if necessary,
then the program can take some error action.  When the 'uncompress'
program tries to uncompress a fake 'file.Z,' it outputs the message:
"file.Z: not in compressed format."  Surely IRAF and other programs
could do likewise after examination of the contents of the file.

The driving force for this thread seems to be a desire to supplement or
perhaps supplant the use of magnetic tape as the standard image trans-
port modality and to begin to consider the _general_ availability of
astronomy images from internet archives and/or on CD-ROM.  Clearly
one must begin to consider conforming specifications for archiving
image data and especially for an efficient retrieval system.  Perhaps
there already is such a system, I'm not the person who would know.
(See the discussion of ODL and ASN.1 etc.)

Here are two tidbits of information I have read in other newsgroups:

        Two CD-ROM Filesystem Formats:  High Sierra and Rock Ridge.
        ==========================
        The High Sierra format is common and also known as ISO-9660
        and characterized by MS-DOS file naming conventions and an
        8-level deep MAXIMUM directory hierarchy.  The Rock Ridge
        format is newer and permits UNIX-style file-naming conventions
        and directory depths.

        Filesystem Name lengths: DOS/8+3 S5/14 BSD/255 bytes.
        =====================================
        The 14-byte length limit for filenames and path component names
        plus the lack of symbolic links are two deficiencies extant
        in my S5 UNIX system for things I would like to do with my AT&T
        3B1 computer.

Regards,
Albert Hybl (hybl at umbc3.umbc.edu)