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I was shown the simplify function of https://mapshaper.org/, which removes unnecessary vertices in polygons. Now I'm looking for a similar function in QGIS and found GRASS generalisation. Since I'm not profound on generalisation algorithms and there are alot of them in GRASS generalisation could anybody tell me which algortihm I have to use to get an equal result?

What Mapshapers simplify does:

After you loaded a file you have a slider to simplify the polygon(s) The great part about is that it removes redundant vertices first and only after that starts to change the geometry. Additionaly the shared borders between polygons stay the same and you get no holes between them.

loaded shapefile

with ~50% vertices removed

high generalisation with most vertices remove

KBuddy
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  • What is the meaning of basepoint in this context? – user30184 Jan 20 '20 at 07:28
  • I mean points which were defined during digitalisation and I want to remove the redundant ones – KBuddy Jan 20 '20 at 07:33
  • i guess node is what I meant. Will edit it. – KBuddy Jan 20 '20 at 07:48
  • What Mapshaper does for a polygon layer is more than just to remove some vertices https://github.com/mbloch/mapshaper/wiki/Topology-Issues. Perhaps you find usable hints from https://gis.stackexchange.com/questions/83855/simplifying-adjacent-polygons-using-qgis-simplify-geometries-tool. – user30184 Jan 20 '20 at 07:49
  • After you loaded a file you have a slider to simplify the polygon(s) The great part about is that it removes redundant vertices first and only after that starts to change the geometry. Additionaly the shared borders between polygons stay the same and you get no holes between them. – KBuddy Jan 20 '20 at 11:51
  • Please [Edit] the question in response to requests for clarification. It's not fair to those who would answer to need to scan a long comment trail for critical information. – Vince Jan 20 '20 at 13:38
  • Screenshots (befor/after) are often helpful. – Jochen Schwarze Jan 20 '20 at 14:06
  • In GRASS GIS, use v.generalize (https://grass.osgeo.org/grass78/manuals/v.generalize.html#simplification-example) for topological simplification/smoothing. – markusN Jan 22 '20 at 08:22

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