Remove partly overlapping geometries from service area in QGIS

Question

In QGIS, Service area (from point) or Service area (from layer) geoprocessing tools create 1 resp. n multipart line features which (usually) contain many overlapping sections.

Most of them can be removed by running Dissolve and Split with lines (with itself) on the resulting service area layer.

However, overlapping lines remain that can't be removed using Delete duplicate geometries.

Here's an example of a service area that has been dissolved and split with lines:

All start and end points of the lines have been extracted as vertices here. I selected two vertices that are start or end points but seem to be located in the middle of a network edge because the respective line makes a "180 degree turn" and then partly overlaps itself. The other few cases with (partly) overlapping lines can be visualized using the "Identify feature" tool. In the following screenshot, only one feature is selected, but obviously there is a start or end point of another line located along this edge:

This seems like a bug within the service area or the split with lines tool—-and leads us to the detailed question:

How can these remaining overlaps (self overlaps and short lines overlapping longer lines) be removed in a performant way?

Delete duplicate geometries obviously only works for complete geometries and I have not found another tool yet to solve the issue.

This question came up when working on solutions for the question Extract all dangles of service areas in QGIS.

Answer 1

1. Multipart to Singleparts the Service area
2. Snap the singleparts to themselves. I use a 2m tolerance
3. Fix geometries
4. Delete duplicate geometries

Answer 2

Here's what finally worked for me:

Description of the algorithms used to clean the service area:

• Multipart to singleparts: Needed for snapping to work correctly
• Snap geometries to layer: Snap singleparts to singleparts, minor tolerance was enough in my case
• Fix geometries: Was not necessary in my case, but it seems valuable to include it
• Dissolve: Dissolve again (here by a temporary ID added for each start point to get separate features in case of multiple start points)

Explanation: Unfortunately, BERA's version did not work completely. Instead of deleting duplicate geometries I had do dissolve the service area to clean it up.

Answer 3

Depending on what you want, dissolving the result might be the quickest and easiest option. You might want to convert multipart to single part features afterwards.

If you still have duplicate lines, then run shortest path network tool on the layer - ideally from all dangles to a point in the center of the network to cover the whole network, but avoid "sidetracks". See here for details.