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In QGIS 3.2 I'm trying to clip a soil map layer and am getting invalid geometry that affects my clip result. The problem appears to be a self-intersecting polygon.

I've tried using the 'check geometries', and can identify the offending feature point, but this tool gives no solution.

Can anyone point me to a walkthrough or advise an easy-to-understand solution?

offending feature

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2 Answers 2

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You can run the fix geometries tool to create a temporary layer. Use that in your processing, or even replace your current layer with it. You could manually get rid of the self intersection by splitting your red polygon on the left near the self intersection and merging that with the yellow polygon, or by splitting either "pincers" of the yellow polygon and adding them to the outer red. If the area split off is pretty small it will have little effect on your acres. Although most of the processing tools in QGIS don't have a tolerance setting, if you use one elsewhere or in v.clean, make sure the split off area exceeds it.

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Got it. Set the invalid features filtering to 'do not filter' instead of 'ignore invalid features'.

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    Hmmm, I've never tried that. Instead, I use Repair Geometry.
    – Stu Smith
    Apr 19, 2019 at 3:30
  • Thanks - shall give it a look
    – Werafa
    Apr 20, 2019 at 9:13
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    Yes IMHO, repairing, or fixing the underlying data problem is a preferable solution. Setting the 'do not filter' flag just ignore's the problem, potentially causing issues later on or downstream.
    – nr_aus
    Jan 29, 2021 at 5:43

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