On the "when" and "where"

[Arnold Rots]

Thank you for your support, Rob.  Time is my priority, too.
Two points:
- STC does tie time to a spatial frame.  ObsDataLocation requires an
observatory location which <TOPOCENTER> refers to; other explicit
spatial locations are in the package as well.
- STC does also include specification of areas in all coordinates -
regions and intervals.

To round it out, spectral and redshift coordinates are included, too,
since all of these coordinates are intertwined, and errors are an
integral part.

  - Arnold


Rob Seaman wrote:
> Arnold Rots writes:
> ...
> > proper STC object (to be precise, ObsDataLocation) would take care of 
> > that.
> 
> ...
> Personally, I'm more concerned about capturing appropriate temporal 
> coordinates.  A scalar time (whether MJD or not) plus an uncertainty is 
> insufficient.  This also currently appears to not be fleshed out that 
> much more in STC:
> 
>      <TimeFrame>
>        <Name>Time</Name>
>        <TimeScale>TT</TimeScale>
>        <TOPOCENTER/>
>      </TimeFrame>
> 
> There still seems to be a focus on scalar time, but the addition of a 
> timescale to correspond to the frame of the spatial coordinates is 
> absolutely critical.  For instance, it is quite likely that there will 
> be a major upheaval in the UTC standard in the next few years.  We must 
> retain the flexibility of using timescales other than UTC.  (Note that 
> this applies equally to derived representations such as MJD.)
> 
> One is confident that an appropriate representation can be found for 
> capturing the celestial coordinates (plus errors and frame) along with 
> a scalar timestamp (plus error and timescale) for a typical point 
> source event.  We must also appropriately characterize less point like 
> events - less point in time as well as space.  Some events will be 
> observed to start, and then to end.  Examples from the draft include 
> solar flares and volcanic activity on IO, but could also include any 
> number of extra-solar phenomena stretching from stellar to 
> extragalactic astronomy.
> 
> ...
> Rob Seaman
> NOAO
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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/
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