STC ObservationLocation

[Ed Shaya]

I vote against optionally entering the location of the observatory. The 
correction to barycenter is dependent on the distance to the object.  
Since in general we do not have direct measures of distances to objects 
this is unwise.  Also, the interpretation of an observation may depend 
on knowing whether the observer was moving, fixed to the ground, in near 
earth orbit, or at L2.


Ed


Jonathan McDowell wrote:

>>will be a formal request for comment period when STC is a PR
>>    
>>
>If this counts as a minor change which doesn't throw the PR back
>to the WG, ok... but really I would prefer if we could
>reach consensus prior to the official PR stage.
>
>Sorry Arnold, but I would also vote for the ObsLoc to
>be optional for coordinate systems which have already
>been corrected for observatory location. In the language
>of the Observation DM, the ObsLoc in those cases has become
>Provenance (check it if you don't trust the data) rather than
>Characterization (what you still need for further work if you
>do trust the data). One could have another STC instance for
>the original as-observed coordinate system in the Provenance
>(optionally!) but the main and required STC would not need
>ObsLoc if everything is barycenter corrected.
>
>Roy and others, note however that some data has some
>things corrected (e.g. velocity frame) and not others
>(apparent position? time?) and so you have to be a little
>bit careful about throwing away ObsLoc. But if the 
>accuracy of the data is such that remaining corrections
>are small compared to the quoted errors, then I think there's
>no problem (e.g. if your time accuracy is 10 minutes, who
>cares if we are in TT or TDB with a 2 ms max difference...).
>This is the sort of thing that should go in a usage guide.
>
> - Jonathan
>  
>