[postgis-users] Combinatorial Boundary ?

[Jeff Lounsbury]

"3.12.3.2
The following geometry operations require some topological sophistication ·
Geometry C_Boundary() - will return the geometry of the combinatorial 
boundary of the current object. For objects of maximum dimension, such 
as areas in 2D, this is the equivalent of the topological boundary. . 
For curves this is the union of the two endpoints. For surfaces, this is 
the ‘edge’ of the surface (which is the boundary of the object as a 2d 
manifold). For complex geometries, we take the “mod 2” union of the 
components. That means that a point is in the boundary of a complex 
object (represented as disjoint representational geometries) if it is in 
an odd number of the boundaries of its component simple geometries."

That might help, I could only find the doc inside the members area of 
the OGC site, so I'm not certain I can post the whole thing...

You might just want the ConvexHull() function, a convex hull is:
http://www.google.com/search?hl=en&lr=&oi=defmore&defl=en&q=define:convex+hull

Cheers,
-Jeff

Arnaud Lesauvage wrote:
> Hi all !
> 
> I am trying to find the boundary of a set of points.
> I don't know whether PostGIS is able to do this or not, but the 
> documentation describes a Boundary() function that is supposed to return 
> a combinatorial boundary "as described in OGC SPEC 3.12.2".
> I can't find this document !
> It is referenced as 96-015R1, but I can't find it !
> I have document 1-101, but there is no description of "combinatorial 
> boundary" in there.
> Could some one explain to me what this boundary is, or where I could 
> find the reference document ?
> 
> Thanks a lot !
> 
> Regards
> -- 
> Arnaud
> 
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