[postgis-users] Postgis topology help

Sandro Santilli strk at keybit.net
Wed Apr 4 14:29:44 PDT 2012

On Wed, Apr 04, 2012 at 12:14:13PM -0700, pcreso at pcreso.com wrote:
> Thanks again for a prompt reply.
> QGIS is showing the results of the inserts & polygonise in the attached image. So, yes, just as you sketched it.

What do you mean by "polygonise" ? Did you use topology.Polygonize ?
Mind you: I'm afraid topology.Polygonize isn't producing valid
edge linking (to be checked and worth updating the manual to point
that out, or to consider it a bug and ticket it).

> I had assumed Polygonize was constructing polygon TopoGeometries ?? Obviously I've missed something somewhere.

TopoGeometries are complexes formed by primitives (nodes, edges,
faces). You may define 5 TopoGeometry objects representing your
5 input lines. 3 of them would be formed by 3 edges each, the other
2 by 4 edges each. You can then use these TopoGeometry objects
like you would use Geometry objects, that is put in tables and
associate attributes.

> I can find no info at all on the ST_TopologySummary() function. Not in the docs, & even Google cannot find a single reference. Where do I look for some explanation of this function (& any others that might be relevant )? 

My fault, not being an SQL/MM function it doesn't have the ST_ prefix:


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