[fitsbits] DATE-OBS: circulate the WCS papers!

[Steve Allen]

On Tue 2002-01-22T14:32:12 -0800, Steve Allen hath writ:
> In effect, we deem DATE-OBS to be broken/deprecated and aren't
> spending any engineering time fixing how we handle it.

This is a plea in hopes that people will circulate the WCS draft
papers to a wider audience for review -- in particular, to the
software teams who will be implementing the keyword capture and FITS
file writing for upcoming data acquisition systems.

The original FITS paper did not assign a precise meaning to DATE-OBS.
The principal investigators in charge of our early instruments did not
prioritize the importance of precise shutter timing; they gave no
specific directives on the meaning of DATE-OBS and time keywords.
The engineers who built the data acquisition system implemented
DATE-OBS and time keywords that minimally complied with the letter of
the standard and with the unexpressed intent of the PIs.
(If we are lucky the imprecise meaning of DATE-OBS has not affected
the interpretations of short-period extrasolar planet observations.)

As a result we feel that we cannot re-engineer newer systems to assign
a precise meaning to DATE-OBS.  If we did it could be mistaken to
imply that the precise meaning applies to older instrument systems.
We feel that we must use privately-defined observation timing keywords
until such time as a WCS paper V or VI comes along to deal with
"Representations of temporal coordinates in FITS".

Nevertheless, there are many keywords in the current WCS drafts which
are relevant to the real-time systems that acquire image data and
produce FITS files.  A review of the WCS papers by instrument
implementors would be good if it can prevent any futher ambiguities
of the sort that we have experienced.

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
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