@Zoltan: I will explain my problem now in detail since I think that this problem could be known to a lot of users:
In Germany we can order cadastre data in a proprietary format from our land surveying offices. To be able to use this proprietary ASCII format with common GIS software we convert the geometry objects with corresponding data into point-, line- and polygon-shapes. Unfortunately the source to convert contains different errors like unclosed polygons (start and end coordinates are not the same), null geometries, incorrect ring ordering, duplicate vertex or self intersections, which are not repaired by the converting tool and therefore lead to errors in the shape files. When I want to use these shapefiles later for spatial functions like a select by location with calculating intersections based on one of these error-shapes, the results can be wrong due to the errors named above. Until now I did not find any software function to solve these problems "smart" with a few clicks except for the geometry repair functions provided by ArcGIS. Even the GRASS v.clean function will not solve the problems listed above. Greetings, Stefan Burgstaller
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