[postgis-users] Dimension of PolyhedralSurface

[Olivier Courtin]

On Aug 11, 2010, at 9:02 AM, Andrea Peri wrote:

Hi Andrea,

> I notice the add of the Polyhedral Surface to GML.
> It is very interesting.

Yeap that's sound promising :)

> But I have a little question:
> see-ing the code I notice the srsDimension of posList is ="2".
> I will think the correct value was "3".

Both are possibles in fact.

> Certainly the value of coordinate used are of a 2D dimension.
> But I don't understand why a Polyhedral surface must have a  
> definition on a 2D universe.
> Or it is the 2D envelope of a Polyhedral Surface ?

Yes it's not so intuitive, but a PolyhedralSurface (as a TIN also)
is first a surface of connected patches.

This surface could be 2D, 3D, 3DM or 4D

And for 3D and 4D the surface could be closed (meaning
that all edge are shared by exacly 2 faces). And in this specific
case the PolyhedralSurface enclose a solid (a cube for instance)


--
Olivier