QGIS Cannot check validity or perform geoprocessing on layers imported from KML

Question

I am using QGIS 2.18.13 on Windows. I have imported some shapes from KML, and saved them to ESRI shapefiles layers. I have tried to perform Vector > Geoprocessing Tools > Difference on some of the layers, but the results are either empty (if I check 'Ignore invalid input features') or an '1006 See log for more details' error. When I View > Panels > Log Messages Panel, I see an 'Uncaught error while executing algorithm' error in some .py Python routines.

The shapes I am working with have the same CRS. When I try to run 'Check validity' on the shapes, I get this error: '-2147483645 See log for more details' and again the log shows an 'Uncaught error while executing algorithm' error.

How can I make these into valid shapes that I can work with an manipulate in QGIS?

Answer 1

Open the processing toolbox in QGIS by selecting Processing > Toolbox. Expand the nodes for QGIS geoalgorithms > Vector geometry tools. Click on 'Change geometry type' and select as your input layer one of the layers with shapes you are having problems with. For 'New geometry type', select 'Polygons' if you are working with polygons (only you know what kind of geometries you are working with), then click 'Run'.

If all goes well, you should see a new output layer called 'Converted' with a copy of the shape(s) from your problematic layer. You should now be able to run 'Check validity' on shapes/features in this new 'Converted' layer without running into the errors you mentioned. You should now also be able to do geoprocessing like 'difference' on these converted layers successfully.