[postgis-devel] Polyhedral Surface / Polyhedron /TINS

[Olivier Courtin]

On Jul 10, 2014, at 1:45 AM, Paragon Corporation wrote:

Regina,

> I think this is a question for you or Vincent Mora.
> 
> I recall you saying there is a bit in the PolyhedralSurface of PostGIS that
> denotes if it represents a volume (Polyhedron).  Is that true or was I
> mistaken.

Yes there's a SOLID bit, meaning that the surface is closed,
and so enclose a volume.

> Also some other questions what are the rules of validity for Polyhedral
> surface and TIN.
> 
> I've always assumed that TINs are really a special class of Polyhedral
> Surface (one composed of all triangles instead of varying size polygons) and
> so the rules that apply to one should be similar to the other.
> 
> I'm guessing
> 
> 1) For both of course the polygon patches and triangles can't overlap

Indeed,

> The others not so sure
> 2) They must share an edge with at lease one other (no islands) -- not sure
> if this is true or not?

There's a no reason for such a thing (must sharing),
A TIN with a single Triangle inside is valid for instance.

But indeed it's the way we check, for now, if the surface is closed or not.

> 3) Are they allowed to share the same edge with more than one other polygons
> and triangles. I wasn't quite clear from CGAL.  Seemed like it was legal
> just a rare occurrence and more representative of a complex polyhedral
> surface.

Humm that's a good question, because if yes the previous closed test
will not fit in this case...

Vincent do you have any input on this one related to (SF)CGAL ?
I will look further in OGC/ISO spec,

O.