[Qgis-developer] Visualizing topology errors and supporting topology editing

[Martin Dobias]

On Sun, Jan 31, 2010 at 2:56 PM, Stefan Keller <sfkeller at gmail.com> wrote:
> Dear list,
>
> I'd like to enable QGIS to visualize topology errors and do more
> sophisticaed topology editing (without GRASS).
> It's something similar to ArcGIS/ArcEditor Geodatabase Topology
> (called topology rules there).
>
> For visualization of errors I would 1) implement a PostGIS validation
> function and put the features found into a new feature class and
> visualize it in a separate layer. See below for some topology rules
> I'm thinking of.
> => Does anyone have experiences with such a Python plugin?

Hi Stefan,

some work on topology checking has been done already: we've been
implementing such plugin within qgis-mapper project. I've extracted
the sources from our private repository and put it on github:
http://github.com/wonder-sk/topol

The user adds some topology rules for various layers, runs the check
and the results are visualized in map canvas. For more info, check
(brief) user and developer documentation in "doc" directory. I would
say the plugin is somewhere around beta stage: it works, but needs
some polishing. It's written in c++ (we've started with python
implementation, but then we've moved it to c++ because it was quite
slow with larger layer). It should work with any vector layers
supported by QGIS, uses geos library for geometry checks. If you'd
like to develop topology checking, this plugin is probably a place
where to start. Currently there's nobody working on the plugin - it
would be great to see some progress with it. Once it's ready for
general consumption, we can add it to c++ plugins that live in qgis
source.

Regards
Martin