7

Check validity in QGIS and Check geometry in ArcGIS Desktop 10.0 give me different results on the following shapefile

ArcGIS does not return an error at the following geometry:ARCgis

but QGIS does when using check validity:QGIS

Is there an official name for geometry errors like this? If they are bad, how should I fix it? I tried QGIS v.clean, manually editing the polygon and ArcGIS repair geometry without success.

BTW the polygon depicted is GU 14917 (Vertex 397)

  • 2
    The name would be self intersection. – RoVo Jun 13 '17 at 14:29
  • this is helpful. – RutgerH Jun 13 '17 at 14:35
  • Please Edit the question to make the ground/figure relationship clearer. If the figure is in blue, then this is a self-intersection, but if the figure is in peach, then this is not a self-intersection, but an inversion, as discussed in these two posts – Vince Jun 14 '17 at 1:27
  • Hi Vincent, I don't quite follow you. do you mean using the same colors in ArcGIS and QGIS? They are currently randomly assigned. – RutgerH Jun 14 '17 at 13:27
3

The problem here is that you have two interpretations of a simple polygon and a self-tangency (intersection of parts at a vertex). ArcMap seems to accept it and the QGIS topology checker not.

I did found some word from the ESRI side here and at least for PostGis i found that it is not allowed here. But for the examples from PostGis for the OGC standard validity for figure j and p they should not be valid due to self-tangency but are written as valid.

Also as far as i understand the OGC standard "OpenGIS Implementation Standard for Geographic information - Simple feature access" the polygons should not be valid because of 6.1.2.2 (IsSimple method). But again valid because of the definition that they may touch in a finite number of points (6.1.14 b) ).

You might choose as well what you want...

  • helpful, is there a way to fix the geometry so that it will be valid for all programs: ArcGIS, QGIS and PostGIS etc.? ArcGIS repair geometry doesn't fix this shapefile – RutgerH Jun 13 '17 at 18:34
  • If you work in ArcGIS I strongly recommend you to convert it to a gdb feature class, which will allow you to use topology. Also, take a look at this: desktop.arcgis.com/en/arcmap/10.3/tools/data-management-toolbox/… – Albert Jun 14 '17 at 6:29
  • Is their a pythonic way to do this? – RutgerH Sep 15 '17 at 18:49
3

It works because it is not a self intersection. That's why you think the repair tools are not working. I checked in both QGIS and ArcGIS and there isn't any self intersection in these features (GU 14917 and GU 15035). If it was a self intersecting polygon you wouldn't be able to separate the vertices like this: in QGISin ArcGIS

ArcGIS is not detecting any invalid geometry in your file once converted to gdb feature class so I assume there isn't any

http://desktop.arcgis.com/en/arcmap/10.3/tools/data-management-toolbox/checking-and-repairing-geometries.htm

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