6

I would like to find all polygons, which intersect another polygon within the same layer. I thought the geometry checker could do the job, but it doesn't.

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All polygons are intersecting except one, but I get no geometry errors. What I am doing wrong? (QGIS 3.8)

  • do you mean intersects? Or just overlaps? Because adjecent polygons with common borders will be selected too if you use the intersects-predicate. – PieterB Oct 22 at 17:44
  • A geometry error occurs when rings overlap each other within a single geometry. You appear to want to validate topology with respect to all other shapes, so your selection of the answer is at odds with your stated goal. – Vince Oct 22 at 22:39
5

I think self-intersections here only refers to intersections within features (with "edge overlappings" if i may say so ...) not between features ... There's a nice tool in SAGA toolbox called Polygon self intersections (... that should be its right name ...) which is doing exactly what u seem to be expecting ....

6

It is better to use Topology Checker tool not Check Geometries. Topology Checker is located under Vector -> Topology Checker, then click on configure button and define a new rule Must not overlap.

Here is an example:

This is a polygon shapefile which has overlap polygons as well as separate polygons.

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Go to Configure in the Topology Checker tool.

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  1. Current Rule: select the polygon layer
  2. Must not Overlap
  3. Add Rule
  4. Click OK

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Click on Validate Extent or Validate All as you like

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Then the overlap area will be highlighted.

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  • Yes, this is working fine to highlight the errors, but unfortunately you can not select them to solve the problems (like geometry checker does) – MAP Oct 22 at 20:02
  • @MAP Yes I agree. Anyway, I am glad you find a solution for your problem. – ahmadhanb Oct 22 at 20:04
5

you can do it with virtual layer and sql.

Assuming that your layer has an id called "id". you can do following query

select a.* 
from your_layer as a, your_layer as b
where st_intersects(a.geometry, b.geometry) and a.id <> b.id

or you can just use 'topology checker'. If you do not see it, just activate it in the plugins

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