WD for the Obscoredata model and its implementation on TAP

[Anita M. S. Richards]

> Arnold - All of this is (except possibly adequate treatment of
> redshift) is already in the full model.  But ObsCore is a simplified
> subset intended only for data discovery.  Agreed something like
> reference position is needed for analysis, but that level of precision
> is not likely to be needed for data discovery.
>
> Fixing the units is essential for discovery, at least if we plan to
> use TAP-ADQL expressions globally.  The primary requirement is that

Why? Conversions are easy and don't even need trig !

all the best
a