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

[Stefan Keller]

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?

For helping to maintain topology while editing I also would implement
this as validation function in PostGIS but are not sure how to
interact between Stored Procedures and QGIS vector editing functions
(at least simply displaying messages from return values of these
functions). => Any help here?

Regards, S.

I’ve compiled following “topology types” so far:
* Area topology cleaning: Eliminating sliver polygons, overshoots,
 undershoots (polygon topology, same polygon class).
* Polygons are non-overlapping (polygon topology, same polygon class).
* Polygons are inside other polygons (polygon topology, two different
 polygon classes).
* Line topology cleaning: Snapping close endpoints
 (vertex-vertex/route topology).
* Routes that share vertices (vertex-vertex/route topology, same
 line class).
* Line objects that share (inner) endpoints (node-vertex topology,
 same line class).
* Line objects that are “connected to” point objects at their
 (outer/inner) endpoints (node-node topology, line and point classes).
* Point objects that share points along line objects (node-vertex
 topology, line and point classes).

Pls. consider "are" (validation) as place holder to be also "should not"
(validation) or "should be snapped to" (cleaning).