I have a set of irregular and curved polygons which I would like to find the centre line of them. I've found some solutions for this problem such as Voronoi polygons but It doesn't work for me. It generates a zig-zag line with too many vertices. I used another solution creating centre lines joining the middle vertices from the short sides but it works well for straight polygons only but not for curved polygons. Adding points along the centre lines with QGIS

Ideally, I would like a simple central line for each polygon with 2 vertices only. Either using QGIS/Graphical Modeler or Python. My target is adding points to the centre line every 3 metres, as you can see on the image.

enter image description here

  • Why don't you use centroids or pole of inaccessibility to create these lines?
    – Erik
    Commented May 7, 2019 at 9:13
  • I've tried to use 'centroids' and it generates points outside the polygon in some of them. Also I've tried the tool 'pole of inaccessibility' and it doesn't create mid points for the longest polygons. Thanks for your suggestion.
    – Senda
    Commented May 7, 2019 at 10:00
  • обратите внимание на эти два решения, я думаю они вам должны помочь, правильно использовать геоинструменты: gis.stackexchange.com/a/295348/120129; gis.stackexchange.com/a/318733/120129 Commented May 7, 2019 at 10:04
  • @Cyril Thanks for that. I'll take a look at this solution.
    – Senda
    Commented May 7, 2019 at 10:47
  • @Cyril Could you explain with more detail the step 4 on your first solution, please? I don't get the same result as you show.
    – Senda
    Commented May 9, 2019 at 15:10

1 Answer 1


Try Thin greyscale image to skeleton plugin:

The Thin Greyscale plugin will thin a greyscale image to a greyscale skeleton image, given a set of levels

  1. Convert polygon to raster with Rasterize
  2. Run Thin greyscale image to skeleton plugin
  3. Convert to polyline using GRASS r.to.vect

enter image description here

  • thanks for your solution. I'll take a look at it.
    – Senda
    Commented May 8, 2019 at 13:11

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