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My goal is to create a buffer from a polygon. But the edges are the problem. I can't really explain it in words, so I will post a screenshot. That's the way I want it to look. So the goal is, that the edges are not connected. The example on the screenshot is done with powerpoint, but I want to do it with QGIS, so I can do it for a lot of polygons at once.

Does anyone have an idea?

enter image description here

21

Starting with a polygon (or several polygons):

enter image description here

Run "Polygons to Lines":

enter image description here

Then "Explode lines". This won't look any different but if you enable "Show feature count" on the Layers list you'll see there's more features, like 4 for every rectangular polygon.

Then "Single sided buffer" on the exploded lines will get you this as long as you buffer on the correct side, which for me was the "Right" side, seen here with the original polygon:

enter image description here

It might depend on which way round your polygon was digitised, in which case you might need to buffer both sides and then there must be another step to work out which one you need to keep...

7

You can convert your polygons to polylines first and then perform a single sided buffer. Both are algorithms that can be found under Processing > Toolbox.

  • 4
    You also need to "Explode Lines" to convert the polyline into a set of single line segment features for buffering. – Spacedman Oct 11 '18 at 14:11
  • @Spacedman, indeed, forgot to mention – PieterB Oct 18 '18 at 7:31
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Taken from here: Have a peek at v.parallel, this might help you out.

  • the problem is, that v.parallel only works with vector lines, not with polygones... – Simon Oct 11 '18 at 13:56
  • But since you're clever you can convert your polygons to singular lines =) – Erik Oct 11 '18 at 14:14
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I followup the same process explained by Spacedman, i use "mmqgis" plugin, it makes me feel more comfortable with many more options than the traditional buffering technique. hope this may help you

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