[postgis-devel] Polyhedral Surface / Polyhedron /TINS

Paragon Corporation lr at pcorp.us
Sat Jul 12 09:02:48 PDT 2014

 >>  For now there's not way to set/get this bit from userland,
 >>  ant it's current internal usage is dedicated to SFCGAL stuff.

 >>  But you're right we could imagine accessors to this SOLID bit,

> >     I can see cases where people would have a closed surfce but would
not want
it treated as a volume. (similar to closed linestring / polygon)

 >  Could you give us examples about this ? 
Well it depends how ST_3DIntersection and ST_3DIntersects behave.  I haven't
exercised them enough with polyhedral surfaces to know.
Take a building for example
You may want the building structure  to be treated as a hollow surface kind
of like a canvas around the building rather than a solid building so that
when you ask if  anything you are planning to put in it
will be obstructed, it will return false for ST_3DIntersects. 
Then again I guess you could treat it as a solid with a hole and have a
slightly more complex geometry
than you normally would.  But I think in most cases its more efficient to
treat as a surface and ensure nothing is within X distance from the surface
(or even a surface that is slightly lower than the dimensions of the actual
if you are only concerned about things inside.
But in some cases you might want it to be treated as a solid because it is a
volume blocked off that no object should penetrate -- like a Flight airspace
where if you are within that enclosed territory you are screwed.
Then again much of what I am saying I suppose could be handled if we had
ST_3DCovers and so forth operators.
If the SQL/MM specs haven't thought about it much maybe not too worthwhile
to think about right now.


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