[fitswcs] Draft WCS Paper V: Time

[Steve Allen]

On Fri 2009-04-03T16:46:58 -0400, Arnold Rots hath writ:
> On EXPTIME: The list of keywords in 3.6 is obviously incomplete (and
> will always be, since it is there for illustrative purposes)

In the case of the exposure keywords I think we really do need a lot
of community review and input.

I am pretty sure that this will end up being a delicate negotiation
between the need for precise meaning and the need to avoid undue
obfuscation of the archival meaning of existing FITS files.

I do not believe that we dare standardize many of the existing
keywords related to exposure time, for their existing use is almost
certainly variant.  Even within the optical instruments at Keck
Observatory we have had to create several documents describing the
meaning of the various time keywords and how they should and should
not be used.

For example, we have
EXPTIME, ELAPTIME, EXPOSURE, TTIME, DARKTIME
In some cases these are corrected for the measured durations while the
shutter was opening and closing, in other cases they are not.
Some are the planned length of an exposure, some are the actual
length.

For a list of the time-related keywords at Keck see
http://spg.ucolick.org/cgi-bin/Tcl/runRpt.cgi?target=KeckObsTime&type=MemeByNam

For a description of the caveats of time-related keywords at Keck see
http://www.ucolick.org/~sla/fits/kecktime.html

--
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