7

I have a self-intersecting line that I tried to split using the Split Features tool in the Advanced Digitizing Toolbar. The problem is that when I try to split the line at one point, the line splits at every point where it crosses over itself.

This line was originally a tracklog generated in WGS 84 using a Garmin GPS. I imported it into QGIS in GPX format, and saved as a shapefile.

The line is styled with a red marker at the first node. Before splitting at the blue circle: enter image description here

After splitting:

enter image description here

What's going wrong here?

1

Looks like this is a long-standing bug (since 2011):

https://github.com/qgis/QGIS/issues/14070

https://issues.qgis.org/issues/4087

  • Thanks for tracking down the bug report. When I asked the original question here, it didn't even occur to me that it might be a bug. The best workaround I found was buffering the tracklog (which doesn't solve the issue, but it met the specific needs for that project). – csk Jul 15 at 21:59
  • I'd love a work around, and the saga tool isn't working for me and the current behavior is costing me hours. – user94812 Jul 19 at 1:46
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The saga tool "split lines with lines" in the QGIS processing toolbox can split lines properly even if they have self intersections.

0

If you only have to do this for a limited number of lines, you can:

  1. Enable snapping (Project --> Snapping options --> Snapping on intersection on)
  2. Turn on the Advanced processing toolbar (View --> Toolbars --> Advanced digitizing toolbar)
  3. Use the Split features tool (enter image description here) by drawing a line through the intersection - it will split both strands of the line exactly where it intersects
  4. Select the two strands that you want remerged and use Merge Selected Features (enter image description here)
  • 1
    This would be fine for a line with only one or two self-intersections. The problem is that a typical GPS tracklog has tens or even hundreds of self-intersections. – csk Jul 15 at 14:06

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