Hi all, If I understood correctly, someone added very recently the support of QgsExpressions in the processing toolbox. This could help I suppose ?
Michael 2014/1/10 Alexander Bruy <[email protected]> > Hi Bernhard, > > there is a good article about Advanced Field Calculator [0], but > only in Russian (there is a Google Translate in the right sidebar). > Hope this helps a bit > > [0] http://gis-lab.info/qa/fieldpyculator.html > > 2014/1/10 Bernhard Ströbl <[email protected]>: > > Hi, > > > > I provided "eliminate sliver polygons" in the processing framework some > > months ago (thanks for your help, Victor!). Eliminate is based on a > certain > > field. You would have to calculate the area (or area/perimeter) for all > > polygons and use that as a threshold in "Eliminate sliver polygons". No > idea > > how to calculate that, though. How does the "Advanced python field > > caluclator work"? > > > > Bernhard > > > > Am 10.01.2014 15:18, schrieb Andreas Neumann: > >> > >> Hi, > >> > >> I don't have a solution for the problem. > >> > >> But I can confirm that the whole analysis chain is a bit problematic > >> with all these precision issues. As an example if you test intersections > >> of buildings against parcels (2 different layers) and the building > >> touches the parcel borders you may get very tiny intersects with parcels > >> (only a few square cms) and you wouldn't want to include these > >> intersections in your analysis. > >> > >> So it would be cool if for geometry tests there could be a notion of > >> threshold values. If the area of an intersected polygon is below this > >> value it wouldn't be taken into account during the analysis. > >> > >> These issues are really kind of show-stoppers and almost always require > >> intermediate steps to sort out these edge cases. It would be very handy > >> if the tools could handle this precision/uncertainty problems without > >> having to do a lot of intermediate steps. > >> > >> Andreas > >> > >> Am 10.01.2014 15:01, schrieb Paolo Cavallini: > >>> > >>> Hi all. > >>> I got into an interesting problem, before opening a few tickets I'd > like > >>> to discuss a line of action. > >>> 1. Some sw (namely geomedia) produces shapefiles with very slight > >>> differences (same layer, modified and exported several times); I > suppose > >>> this is due to truncation/approximation in coordinate precision. > >>> 2. As a result, the diff between these layers produces a number of > >>> virtually 0 width polygons, and some topological errors. > >>> 3. This in turn leads to 2 problems: > >>> 3.1. subsequent analyses fail because of the errors, and the user has > no > >>> clue about the reasons > >>> 3.2. The microareas are tricky and time consuming to remove (if they > are > >>> isolated, a possible solution is to select and remove those smaller > than > >>> an arbitrary threshold, but if they are linked to some "real" polygons, > >>> this will not work). > >>> I would therefore suggest a few improvements over the toolchain, i.e.: > >>> * add a parameter in analyses, to either snap original data within a > >>> threshold before running the analysis, or to clean up the results > >>> afterwards > >>> * check& warn the user of topo errors in source layers, and of > possible > >>> > >>> wrong results; maybe this should be optional, as this will slow down > the > >>> analysis, and may be useless after first cleanup. > >>> > >>> Sample data available for those interested. > >>> > >>> All the best. > >>> > >> > >> _______________________________________________ > >> Qgis-developer mailing list > >> [email protected] > >> http://lists.osgeo.org/mailman/listinfo/qgis-developer > >> > >> > >> __________ Information from ESET Mail Security, version of virus > signature > >> database 9274 (20140110) __________ > >> > >> The message was checked by ESET Mail Security. > >> http://www.eset.com > >> > >> > > > > > > > > __________ Information from ESET Mail Security, version of virus > signature > > database 9274 (20140110) __________ > > > > The message was checked by ESET Mail Security. > > http://www.eset.com > > > > > > > > _______________________________________________ > > Qgis-developer mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/qgis-developer > > > > -- > Alexander Bruy > _______________________________________________ > Qgis-developer mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/qgis-developer >
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