[postgis-users] topology example

[Sandro Santilli]

On Tue, Feb 28, 2012 at 05:06:10PM +0100, Denis Rouzaud wrote:
> Hi Sandro,
> 
> Thanks a lot for your attention.
> I did not had so much time to look deeply into it these two days.
> 
> So far, I could not perform make check correctly due to some
> passwords problems.

You might need to play with environment variables for setting password

NOTE that I just committed a fix for the problem you were having.

> Basically, I have a database in oracle (non spatial) in topobase
> (autocad) with pipes. I am migrating the whole thing to use Qgis to
> manage the network.

You're probably looking for network topology then, which is not
the kind supported by PostGIS core. We do planar topology for now.

> So I collected all the given errors when using toTopoGeom to first
> correct the geometry in autocad, then re-importing and re-creating
> the topology again.

The idea of toTopoGeom is it never reports errors...

> I don't really understand how the topology is handled in postgis and
> what is for example written in the topogeom column.

You get a TopoGeometry value, which you may think of as a special kind
of Geometry and threat as such (it casts to Geometry). The postgis wiki
contains more informations about the details.

> There is still one main point which I don't understand. Why is there
> any control on the topology if there is validateTopology function?

There are more and less expensive controls, at different levels.
What you did hit was an internal consistency check that revealed a
conceptual bug in the code.

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