I have a quite difficult issue: I need to simplify polygons, but without "trimming" them - no parts of polygon can be lost; furthermore, all holes in polygons should be filled (but this last is less important and can be done by hand). I presented an example of what I need - the brown polygon is original, and the red outline is desired extent.

There is a significant amount of similar questions on the StackExchange, but answers were not sufficient.

I use QGIS 2.18.3 and I made some trials using SimpliPy plugin - but results using tolerance: 10 are not so satisfactory. Second picture presents it: in some places work has been done well by the plugin, but some parts are excessively simplified. Also, there are parts that had not been simplified.

I wonder whether I should just try with SimpliPy settings and parameters - or should I look for another way (maybe GRASS / SAGA algorithms)

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  • Maybe are you looking for a smoothing operation, instead? – mgri Mar 29 '17 at 8:45
  • With one exception this rule works: take three vertices and remove one in the middle of they make right triangle outside original. Simplify first with 0 offset to eliminate extra points if any on straight segments. Doable if you know how to work with geometries – FelixIP Mar 29 '17 at 9:04
  • Mapshaper does topological simplification github.com/mbloch/mapshaper , it's available via R (probably Python too somewhere): github.com/ateucher/rmapshaper – mdsumner Mar 29 '17 at 9:16

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