A Proposal for a TIMESYS Element in VOTable

[Arnold Rots]

I maintain that the better way to indicate the actual time stamp value
(i.e., not the TIMESYS) is to use well established representations.
Both JD and MJD are officially recognized by the IAU, while the limited
ISO-8601 is a convenient user-friendly representation that has the blessing
of the ISO.
I grant you that a fourth representation, elapsed time (the only one that
requires a unit), is needed and that it requires a time origin, but it is a
bit silly to require a time origin for an officially recognized
representation like MJD.

So, I would suggest adding to TIMESYS an attribute like
origintype=JD|MJD|ISO and to the timestamp an attribute like
timetype=JD|MJD|ISO|ELAPSED and requiring the timeorigin and the unit only
to be present for timetype=ELAPSED.

For one thing, this is consistent with FITS WCS usage.

I was puzzled by the very last example of Section 3. It claims to provide a
time stamp in MJD, but it is actually provided as ISO-8601.

Finally, I am not really happy with the choice of the name TIMESYS, as this
is used in FITS WCS with a different meaning. TIMEFRAME might be a better
choice.

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 cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
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On Wed, Oct 31, 2018 at 9:25 AM AdaNebot <ada.nebot at astro.unistra.fr> wrote:

> Dear All,
>
> A Note entitled “*A Proposal for a TIMESYS Element in VOTable*” can be
> found under:
>
> http://ivoa.net/documents/Notes/TimeSys/
>
>
> Thanks for taking the time to read this document,
>
> Happy reading!
>
> See you in College Park,
> Ada Nebot
> TDIG Chair
>
>
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