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I'm trying to intersect two vector layers (having the same CRS EPSG:4326 WGS 84, in QGIS 2.18.10) but I get this error in the log:

Input layer A contains invalid geometries (feature 52). 
Unable to complete intersection algorithm.

I have checked the validity of both layers and in both cases there are no errors or invalid geometries. Nevertheless, I have deleted feature 52 of the layer with the invalid geometry, and when I intersect them again, I find an error on feature 51, and so on until I delete every single feature.

  • Is there a way to check for errors in the geometry other than 'check validity'?
  • Could it be another type of error that QGIS is trying to indicate?
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    What kinds of datatypes are you using? It might be helpful to post examples of your datasets
    – wmebane
    Commented Jul 25, 2017 at 18:41
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    thank you for the suggestion @user2913671 , but being new to qgis I don't know what datatypes means. Is it the type of layer that I'm working on? or the variables in the attribute table? If its the latter, is it related to the geoprocessing?
    – Camila Burne
    Commented Jul 25, 2017 at 19:02
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    To check geometries, use Topology Checker plugin and then v.clean from grass toolset to solves those issues
    – aldo_tapia
    Commented Jul 25, 2017 at 19:32

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Just had same problem. Options that I found trying to identify problematic polygons: - Topology checker plugin - Geometry validator plugin - Geometry Checker plugin. In my case problems were in self intersecting polygons which did not all show up in output of Check validity. Geometry Checker plugin might be useful in some cases to find and fix invalid geometries but you need to specify tresholds. Only way i could find to fix my data (manualy was not the option)was by using qgis 3 processing tool, Fix geometries.

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    As per tag defined, Camila explicitly uses QGIS 2.18. Changing the QGIS version from 2.18 to 3.0 (for only one problem described above) can cause some issues, due to the use of some (own) plugins and so on.
    – Stefan
    Commented Mar 13, 2018 at 9:53

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