[fitsbits] WCS Paper III MJD-AVG vs. DATE-AVG

On Fri 2004-10-22T14:02:16 -0400, Doug Mink hath writ:
William Thompson wrote:
One of the keywords introduced in this paper is MJD-AVG, representing the
average time of the observation. If MJD-AVG is absent, then DATE-OBS is
used in

I second this. All of my code which deals with timing already has to deal
with both
Julian Dates and ISO 8601 dates, so implementation of the more human
readable
DATE-AVG would not be difficult. If both are allowed, would the standard
have to
require that one take precedence over the other if both are present?

The tricky part here is that this begins to tread on the grounds of a
supposed subsequent WCS paper (WCS Paper V?) which seems likely to
have a title something like "Representations of temporal coordinates
in FITS".

The meaning of "average" in paper III is intentionally not defined.

There should presumably also be keywords akin to DATE-BEG and
DATE-END, but it is highly unlikely that these will go into paper III.
Most of all, a way of declaring the time scale being presumed for any
date-time is needed. But given that there is a raging international
battle going on in the precision timing community, the FITS community
is not likely to agree on such things in short order.

--
Steve Allen UCO/Lick Observatory Santa Cruz, CA 95064
Voice: +1 831 459 3046 http://www.ucolick.org/~sla
PGP: 1024/E46978C5 F6 78 D1 10 62 94 8F 2E 49 89 0E FE 26 B4 14 93

On Fri 2004-10-22T11:42:59 -0700, Steve Allen hath writ:
The tricky part here is that this begins to tread on the grounds of a
supposed subsequent WCS paper (WCS Paper V?) which seems likely to
have a title something like "Representations of temporal coordinates
in FITS".

The other tricky part is what would DATE-AVG look like in
table 13 of WCS Paper III.

MJD-AVG becomes MJDAna

DATE-AVG would be ?

DATAna is mnemonically confusing

DTAVna to be read "date/time average" is better
but loses contact with the "DATExxxx" tradition
already in the standard.

Note that the "n" corresponds to column number and the "a" is there
for the sake of the supposed WCS Paper V so as to permit different
time scales (or even different relativistic reference frames) to be
used for different versions of the WCS.

--
Steve Allen UCO/Lick Observatory Santa Cruz, CA 95064
Voice: +1 831 459 3046 http://www.ucolick.org/~sla
PGP: 1024/E46978C5 F6 78 D1 10 62 94 8F 2E 49 89 0E FE 26 B4 14 93