[fitswcs] Time WCS (Clarification)

[Arnold Rots]

Looking at some of the comments I received, it may be good, in order
to prevent misunderstandings on the more trivial items, to clarify
what we used as guiding principles in choosing keyword names and values:

1. Follow existing keyword conventions that stem from the Y2k
   agreement or that are in wide-spread use.

2. Don't use a keyword that has different meanings in different
   conventions.

3. Try to be consistent with papers I-III.


As to the first, there are two major sources: the recommendations from
the FITS Y2k agreement and a number of concepts from the HEA community.
Together these were used for RXTE, a timing mission, and, as it turned
out, the resulting set offered a consistent framework that satisfied
the requirements of precision timing. This served as a good starting
point for the time paper, but it explains the pedigree of some of the
keywords.

#2: That's why keywords like EXPOSURE and EXPTIME cannot be elevated
to standard status - they are a lost cause.
Clearly, Section 3.6 needs to be fleshed out further with examples
from other parts of the spectrum and, possibly, additional new
keywords.

#3: I don't like "GEOCENTE", but that's what Paper III made standard.
Nor do I like the somewhat obscure shortening of "systematic error"
and "random error", but again, that's what previous papers came up
with.


Cheers,

  - Arnold

--------------------------------------------------------------------------
Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
--------------------------------------------------------------------------
----- End of forwarded message (env-from arots) -----
--------------------------------------------------------------------------
Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
--------------------------------------------------------------------------