[fitswcs] WCS documents

[Mark Calabretta]

On Mon 2001/10/15 09:23:21 +0100, Clive Page wrote
in a message to: "fitswcs at primate.aoc.NRAO.EDU" <fitswcs at primate.aoc.NRAO.EDU>

>I think there's a more general problem here, in that it's quite hard to
>work out _how_ to extend the FITS Standard in a way which is compatible
>with existing files and existing software (not to mention the existing
>Standard).

The IT world abounds with examples of software adapting to evolving language
standards.  Try feeding a FORTRAN 90 program into a FORTRAN 66 compiler!
ANSI C into K&R C.  HTML 3.2 into an old browser.  LaTeX2e into a LaTeX 2.09
processor.  java.  PostScript.  C++.  perl.  tcl/tk.  glish...

"Once FITS always FITS" requires new FITS readers to parse old FITS files,
not vice versa.  If the software can't (or won't) adapt then the language is
dead in the same sense that COBOL is dead.

One conclusion to draw from this is that FITS needs a version number.
Perhaps the NOST version number would serve as the value of a FITSVERS card.

Mark Calabretta
ATNF