Subject: Re: DATE-OBS='31/12/99'

From: Peter Bunclark <psb at ast.cam.ac.uk>
Date: Fri, 28 Jun 1996 15:21:55 +0100

Time for a summary.  My original message was to ask for something to 
be done about the lack of a century in the DATE-OBS format.  I pointed out
that the problem has been current for some time, since we already really do
produce FITS tapes of date spanning more than a century.

My suggestions of DATEOBS and CENT-OBS were only ideas, not strong proposals.

Guy Rixon doesn't like those DATEOBS and suggests DATEFULL or DATELONG
or DATE-ISO.

Rob Seaman came up with a bunch from the WCS discussion:
 MJD-OBS MJD-REF MJD-BEG MJD-AVG MJD-END MJD-WCS
        DATE-OBS TIME-OBS DATE-END TIME-END TIMEUNIT
        TIMESYS TIMEREF
        OBT_TIME
        DATE_OBS = 1995-11-16T21:21:15.721Z
but he suggests extending DATE-OBS to allow a 4-digit year.

Mike Corcoran doesn't want to mess with DATE-OBS and suggests adding YEAR-OBS.

Steve Allen expands the quest to timescales both longer and shorter than
my original ideasr, and he goes over the argument for MJD-OBS being
definitive but not human-readable.

Guy then suggests standardizing on MJD-OBS and throwing away DATE-OBS.

Preben Grosbol comes in with general agreement, and promises to post the
ISO 8601:1988/1991 general time format.  Preben next argues not to violate
the original DATE-OBS, nor even the DATE... format and suggests OBS-DATE.

Frank Valdes comes in with the assurance that by 2000 old FITS readers
can be modified where necessary.  He supports both MJD-OBS and a human-
readable ISO date.

Rob then returns, disagreeing with Prebeb by saying that of course we
can alter the definition of DATE-OBS, and points out one of the 
shortcomings of Wells et al (1981)  (PAPER ONE).

In conclusion, we all agree there is a problem to be fixed, but not on
much else.  I would like to add some further points:

1) PAPER ONE did contain a few howlers (EPOCH being the most celebrated),
   and so cannot be considered inviolate.  The phrase "the form 'dd/mm/yy'
   (which is as good a system as any of the others)" is not only incredibly
   flippant in the context, but quite inaccurate.  We've been discussing at
   length the problem of a 2-digit year; also, the slashes are redundant, 
   the day-month-year order is confusing to Americans (easily done),
   and the order is little-endian.

2) I would deprecate DATE-OBS from 1/1/2000; if FITS writers leave it out,
   then old FITS readers won't misinterpret it.

3) DATE-OBS = 'dd/mm/yyyy' is going to cause a lot of grief to old 
   software.  And much of this old software is sitting on old systems
   in operational situations and nobody dares touch it...

4) I feel strongly the proposed new format should be most-significant
   first;  it is convenient in many situations to be able to do a 
   meaningful sort on the ascii collating sequence.

5) I feel strongly about the FITS standard, despite its various shortcomings
   (8-character keywords is my favourite, right up there with the lack
   of an unsigned data-type).  However, we're about to write a new
   FITS writer for a major observatory (ING La Palma) and will not 
   let it out with the century ambiguity outstanding; any chance
   of reaching a consensus here?

Cheers,
	Pete.