I have polygonised a viewshed and as a result, I have small 1x1 holes on the perimeter of the output which has created overlapping nodes (although the node tool does not pick up on it). The screenshot below illustrates the issue and, although I can not prove these features are the cause for the invalid geometry, it is the only cause I can think of. I have ran the mulitpart to single part command and the check validity tool picks up on the polygon as invalid. I have never used the grass v.clean tool before and I was hoping to get some direction/advice as to which process to use.

enter image description here

  • 1
    Related: gis.stackexchange.com/questions/135871/… – Vince Nov 17 '17 at 15:02
  • This seems to be related and includes some instructions :gis.stackexchange.com/questions/112687/…. Perhaps the other way to do this is to extract the holes in the polygon, then re-clip the main polygon. I would try out the automatic method first though. – Martin Nov 17 '17 at 15:34
  • I tried with v.clean with no success once, maybe I got lost in all the features of it. I could fix them manually since they were not too many. You are facing a topological error: a polygon cannot have two nodes falling on the same coordinates; maybe using 8 connectedness in gdal_polygonize.py (your qgis polygonize function) – Elio Diaz Nov 17 '17 at 22:38

Your Answer

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

Browse other questions tagged or ask your own question.