3

I have imported a layer which contains a lot of lines. They overlap each other in a cross kind of pattern. When zoomed out it can look like this:

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When zooming in on one of the broader lines it looks like below, where the thicker black line indicates my wanted output?

Is there a way of identifying what lines that overlap each other and merge them to one line that stretches across where they are? It is also OK with a straight line if the curved is not doable:

enter image description here

The background is that the lines comes from a tool called Kartapullautin and are representing cliffs from LIDAR data. I want them to be merged so I can easily add it to a map and not have thousands of small cliffs on top of each other, but rather have a few simplified one. Both from readability purpose, but also because the large amount of cliffs are growing my map project in file size so it is difficult to work with. It is worth to mention, I am QGIS newbie!

  • Hi Andre, thanks for the advice. I'll think about that for the next post. But have you changed the wording in my text as well? I do not recognise the text I wrote yesterday and it does not seem to by my way of expressing myself in forums. – StefanK Jul 21 '16 at 5:46
  • Any new ideas to how to solve this? I have looked myself some more into this issue but do not find a solution. – StefanK Mar 31 '17 at 14:38
2

Let's give it a try, anyway.

  1. Sample cliff lines (manual drawing)
  2. Extract points at intersections: QGIS Geoprocessing Tools | QGIS geoalgorithms | Vector oveerlay tools | Line intersections
  3. Generate concave hull: Concave Hull Plugin
  4. Draw Skeleton: QGIS Geoprocessing Tools | GRASS GIS 7 commands | Vector | v.voronoi.skeleton

enter image description here

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A gotcha is seen at the end of the line...

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  • Great, that moved me closer to the solution than I have ever been before! I get the first part right with the intersections. But when I build an area I get one large area for my whole map. Not one area per cluster of lines that I wished for. I played around with the settings without managing to get it right. Any ideas if this can be done? Here's an original file with the lines from one of my areas: dropbox.com/s/jdh7z8jibccepo2/merged_c3.dxf?dl=0 The result should be a mix of green lines from above replacing clusters and the singel lines without intersecting other lines. – StefanK Dec 7 '17 at 13:05
  • @StefanK Thanks sharing your data. It came to my attention that the intersection between lines are relatively scarce. You may as well skip the Step 2 and directly create concave hull. Secondary, Concave Hull is very unlikely to create single large hull. I am afraid you had called up Convex Hull function for some reason.(Concave Hull is found under Vector | Concave Hull. – Kazuhito Dec 7 '17 at 17:27

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