[geos-devel] Small gaps between results of GEOSDifference?

Marco Hugentobler marco.hugentobler at sourcepole.ch
Sun Feb 17 23:02:10 PST 2013

>I was looking for a way to programmatically enable
>'topological editing' while editing "TopoGeometry" layers in qgis.
>If you can help there I'm all ears :)

This is stored as a project property. So you can do:
QgsProject::instance()->writeEntry( "Digitizing", "/TopologicalEditing", 
true )

QGIS then tries to find matches for each vertex of a geometry, using 
tolerance 0.0000001 for degrees, 0.001 for meters and 0.0001 for feet.


On 15.02.2013 18:29, Sandro Santilli wrote:
> On Fri, Feb 15, 2013 at 05:33:53PM +0100, Marco Hugentobler wrote:
>> Hi Sandro
>> Thanks for explaining this. In the short term, it seems best to me
>> to always enable 'topological editing' in QGIS together with avoid
>> intersection. That way, the intersection vertices are added to both
>> geometries.
> Speaking of which, I was looking for a way to programmatically enable
> 'topological editing' while editing "TopoGeometry" layers in qgis.
> If you can help there I'm all ears :)
>>> Exposing fixed precision to the C-API is on the TODO list for 3.1 so if
>>> you want to help with that you're very welcome. It will take exposing
>>> a new PrecisionModel abstract class and provide means to attach them to
>>> GEOSGeometry objects.
>> So basically the subclass of PrecisionModel will do the rounding?
> That's what it should theoretically happen. Noding will be performed
> based on the given precision grid so the segment and the vertex will
> be found to be "intersecting" and consequently noded when building
> the second topology.
>> Looks like a very clean approach to me, I'm looking forward to the
>> new version.
> Will be a long way.
> --strk;
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Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee

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