[postgis-devel] Validity flag

[Even Rouault]

> Does OGC (or ISO) today say what makes a 3D geometry
> valid ? I'm guessing it's not just a matching Z for first and last
> point in a ring ...

OGC 06-103r4 Simple Feature Access Part 1 v1.2.1 [1] mentions in §6.1.11.1 : 
"A Polygon is a planar Surface....". And SQL/MM-Part3 [2] says the same thing 
in §8.3.1: "The ST_Polygon type is a subtype of the ST_Curve Polygon type and 
represents a planar surface..."

The notion of planar surface isn't defined in those docs. Presumably in 
others. But I guess it means that the (x,y,z) coordinates of the vertex much 
be solutions of an equation ax + by + cz + d = 0

Even

[1] http://portal.opengeospatial.org/files/?artifact_id=25355
[2] http://jtc1sc32.org/doc/N1101-1150/32N1107-WD13249-3--spatial.pdf

-- 
Spatialys - Geospatial professional services
http://www.spatialys.com