I'm working on some shapefiles in both ArcGIS 10.2 and QGIS 2.0. I have 3 files which I have cleaned of self intersections in ArcGIS using Repair Geometry. I have also checked for Overlaps using the Analysis tool. A complication is that I have a few “correct” overlaps I need generated from a powerline tenement crossing mining tenements which need to be in the same file so it’s going to be a bit of a pain to pull out the “errors”. I assume overlaps are not part of a “geometry” issue.
I understand from other articles that the best way to get rid of overlaps, etc is to convert the shape files to file-geodatabase and build the topology in ArcGIS for "Must Not Gaps" and "Must Not Overlap". However this may cause problems with the polygons that I need to overlap. I'll experiment with this.
When I bring the shapes into QGIS and use the Topology Checker I get 3 Invalid Geometry messages related to a whole lot of exploration track polygons. I also use the No Overlap and this works fine in picking up the overlaps .
My question relates to the issues with the geometry differences as nothing is obvious and it's not related to things such as overlaps/gaps. I’m a bit puzzled about this invalid geometry error which is apparently NOT picked up by the ArcGIS check. If I can’t work this out I may post this for people to look at and maybe give me some idea as to what is going on. Tolerance differences between the algorithms in the respective programs have been mentioned as important and I’ll look at this as well.
PS I have also used the QGIS Check Geometry Validity tool. This gives 2 duplicates (none flagged using the Must Not Have Duplicates in the Topology Checker), as well as a number of intersects. Are these real as I thought I had removed these with ArcGIS. Ahhh...no wonder this gives people headaches.