Charac Answer

[Anita Richards]

>
> It may sound strange, but ObservatoryLocation is actually part of the
> coverage.  I'll grant you that it makes no difference for
> far-field objects, but it is essential for doing research on
> near-field objects in far-field observations and vice-versa -
> especially if you have a spacecraft that goes regularly a third of the
> distance to the moon.
> In addition, the ObservatoryLocation (and particularly its
> time-derivative) is essential for redshift and spectral analysis.
> Coverage pertains to all coordinate axes.

I take Arnold's point completely, I agree that it should be in the 
Observation data model, but I am not sure that it is specifically part of 
characterisation; for example, in interferometry, the resolution which 
results from the telescope separation is the releveant measure to be in 
Characerisation,; the actual telescope positions belong elsewhere, I 
think.  We need to distinguish between whre models ned to be comprehensive 
and where they need to serve specific purposes of accessibility.  If an 
optical astronomer wants a radio image, s/he will not have the software to 
cope with telescope positions and possibly neither will any VO intermediat 
layer; that is the job of a specialist data provider.

In short, we do need extremely comprehensice models like STC but we also 
need (consistent) specialised models which are not overloaded with 
elements which they can get from elsewhere.

cheers

a