Boxes and Polygons in ADQL/STC. Questions and recommendation.
patrick.dowler at nrc-cnrc.gc.ca
Mon Oct 26 07:55:40 PDT 2009
On Monday 26 October 2009 06:58:51 you wrote:
> Patrick Dowler wrote:
> > Note that postgresql+pg_sphere has the same limitations (except sbox, so
> > have to use spoly directly); I also found that both STC-S and pg_sphere
> > are limited to simple polygons and do not support unions of disjoint
> > regions or holes inside polygons.
> Hi Pat,
> Could you expand on this? That's not surprising for PgSphere which
> doesn't purport to do anything more than circles and polygons (and its
> boxes in a limited way), but I had understood that REGION's could be
> quite complex. Is that not the case?
> I think I still need the first type, but from your comments it sounds
> like any REGION currently specifiable can be represented as a single
> polygon. Is that right?
STC in general does allow for such complex regions, but the STC-S
serialisation does not support the "operators" (add,subtract, etc). so you
cannot describe something like several disjoint shapes as a single region.
See the last paragraph of Section 3 in
So while you could have such FOV in your system (we do, with a 1-n join
between the main table and a "PositionSamples" table with the spoly column)
you cannot write them out as a single STC-S value in the result VOTable. That
was what I meant.
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