STC ObservationLocation

[Arnold Rots]

Roy,

You may recall the discussion we had about this last Thursday and I'll
repeat what I said then.
If you say BARY, it means you have applied a transformation.  And that
transformation is based on model assumptions.
There are a number of applications where it is crucial that users can
undo that transformation (the obvious one being pulsar timing).
And since it is a matter of just a single boiler plate line, it seems
a minor inconvenience.  Besides, I suspect few VOEvents would warrant
or provide barycenter-based coordinates.

  - Arnold


Roy Williams wrote:
> Arnold
> 
> I would like to ask a question about the structure of the STC system,  
> in particular it is the old chestnut about the element  
> ObservatoryLocation.
> 
> Of course, if I specify that the coordinate frame is centered on  
> TOPO, then it means I need to specify where that center is -- i.e.  
> the observatory location must be specified. Even for very distant  
> objects, the timing information cannot be accurate without this.
> 
> BUT
> 
> Suppose I specify that the coordinates are in GEO (geocentric) or  
> BARY (barycenter of solar system), then why it is necessary here to  
> say where the observation was taken? Is it just that the XML schema  
> is too coarse to make this fine distinction? Or is there a subtle  
> matter of coordinate accuracy that I have missed?
> 
> Roy
> 
> California Institute of Technology
> 626 395 3670
> 
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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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