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I have a set of points as well as a line layer (a road network) as given below.

Point and line layers

After I snap the points to the line layer the result is as follows.

Points snapped to lines

The result that I need is to clip/trace the line layer segment spanning the point layer like this:

Traced line layer

I've tried many methods on QGIS from using a buffer on the snap points to clip, to using join attributes by nearest/location, however due to the inconsistency of the placement of the points on the line layer I always end up with many gaps, unnecessary segments. I am also unable to use the points to path feature because the points don't have an attribute which indicates order.

What's the best way that I could try to achieve this result? I'm willing to even venture into solutions outside of QGIS (GRASS, GeoPandas) as long as it's open source.

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  • You could add the ascending ID manually?
    – Erik
    Commented Aug 30, 2022 at 11:37
  • 1
    Without having your data this is impossible to solve
    – Bera
    Commented Aug 30, 2022 at 12:19

1 Answer 1

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You can do that with Network tools. Use Menu Processing > Toolbox > Shortest Path (point to layer) (see documentation) with these settings:

  • as Vector layer representing network, use your line layer.
  • for Start Point, click on the first point (use activated snapping to "catch" the point)
  • for Vector layer with end points, use your points layer - no need to snap them to the line beforehand.

However, you need a proper network: where lines intersect or touch, they must have a common vertex for the tool to find a connection between lines. Alternatively, expand Advanced Parameters and set a (small) topology tolerence.

When you run the tool, you get the desired output - see screenshot below.

Be aware: If you want to clean the result, explode the lines and delete duplicate geometries. If necessary, re-merge the lines and convert from Multipart to single parts to get simple lines as output.

Screenshot: yellow lines created based on black input network and red points:

enter image description here

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  • Thanks. I tried this but I seem to end up with many extra segments: imgur.com/V5HZfnY
    – Nandula
    Commented Sep 2, 2022 at 4:06
  • From the Image it does not become clear which lines are Desiree outputs and which not. Can you add details? Can you share Project + data?
    – Babel
    Commented Sep 2, 2022 at 5:45

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