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.

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    Is there any chance you could insert description/picture on shapes that are reported as incorrect? – Alex Tereshenkov Jul 7 '14 at 9:39
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    Clicking on the error message in QGIS' topology checker will bring you to the potentially problematic vertex or line. Do any problems show up when you check manually(most probably zero-length lines or overlapping geometry)? I can also imagine that ArcGIs and QGIS topology use different tolerance values (in this case, QGIS would have narrower ones...) – SAnderka Jul 7 '14 at 11:19
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    You should also know that some parts of the shapefile specs are vague, and different software assume different things. Example: spatiallyadjusted.com/2012/12/07/ogr2ogr-every-shapefile – Devdatta Tengshe Jul 7 '14 at 11:45
  • Thanks folks, Have tried to clarify the question including what I've looked at. Essentially it is ...why does ArcGIS essentially say the SAME file is ok and QGIS doesn't like it. Devdata cheers for link, I'll look at ogr2ogr. – DirkB Jul 8 '14 at 8:10

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