3

I used the very nice "Fix Geometries" tool in the Processing Toolbox of QGIS 3.6 to repair a vector layer that was giving me trouble. The tool in QGIS worked just fine, but I was hoping to find out the actual algorithm or Python/C++ code used to implement this feature. I was wondering if anyone knew what code was used to actually implement this tool and fix geometries. Or if there is a different an better way to fix the geometries, any such recommendation would work too.

So let me explain a little bit. I did look up the QGIS documentation for the "Fix Geometries" tool in the Processing Toolbox. Unfortunately, that documentation does not explain how it fixes the geometry--meaning the algorithm. Here is a little excerpt from the documentation:

Fix geometries

Attempts to create a valid representation of a given invalid geometry without losing any of the input vertices. Already valid geometries are returned without further intervention. Always outputs multi-geometry layer.

I also looked in the Log window of the Fix Geometries tool, but it did not seem to show the GDAL code or such, as in other tools.

In the past I have resolved this issue by wrapping a narrow buffer around the geometry of interest, to overcome invalid geometry errors. Of course this does create some errors in the resulting layers. However, I saw that the Fix Geometry tool did not seem to add a buffer, and hence seemed to solve the invalid geometry problem without introducing some error. Hence I was wondering if anyone knew the code behind that tool.

3

The code is in GitHub. The Fix Geometries tool is a wrapper to the function LWGEOM_GEOS_makeValid, which then calls different functions for different geometry types. You can read the various LWGEOM_GEOS_makeValid* functions such as the polygon one in the file qgsgeometrymakevalid.cpp

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.