Creating centerline of river in QGIS?

Question

I made two river bank lines and I want to associate them.

I want to make a centerline using two rows as a base. I managed to make the centre line with a lot of work creating several lines from one margin to the other of the river and then using the centroid, but this solution is very tiring and I have to do this in several areas.

I think after 6 years a new question is legit and answers provided are not up to date for version 3 — MrXsquared, Apr 16 '19 at 20:49

Cyril Mikhalchenko · Answer 1 · 2019-05-14T16:46:34.627

The surest method for solving your question from the point of view of the cartographic approach is to use the Voronoi Polygons.

I offer one of the solutions to your question using QGIS tools.

So, the initial data is a river as an areal object, see the figure below.

2) Vector > Geometry processing > Convert polygons into lines, see image below

3) Open the closed line QGIS "Split Features" tool and run the GRASS v.split tool, so that the points are evenly distributed along the line and run the Vector> Geometry Processing> Voronoi Polygons tool on them, see the figure below

or run the plugin with the name in the screenshot below, which is more convenient ...

4) Cut the original Voronoi polygons from the result with Vector > Geoprocessing > Trim and then select only one half of the river area, see the picture below using the Ctrl key and the selection tool more Vector > Geoprocessing > Merge by grounds ... > By all indications.

5) Cut from the source layer the result of the selected left or the right area, see the picture below.

6) Then from the result of cutting create a line, blow it up, remove unnecessary parts and leave the centre line of the river, see figure below

This is the main approach to solving your question and it is clear that a variety of tools allows you to solve your question in various ways, but the idea remains the same, good luck ...

This is a great solution. Have you been able to automate this in Python? — Aaron, Dec 05 '19 at 18:01
@Aaron, Unfortunately, I haven't studied Python yet, but I'm closer to Postgres/PostGIS :-)... — Cyril Mikhalchenko, Dec 05 '19 at 18:30
@Aaron, I implemented this technique in geoSQL (as I call PostGIS) and its result is different from the ST_StraightSkeleton and ST_ApproximateMedialAxis functions... — Cyril Mikhalchenko, Jan 03 '20 at 20:18

csk · Answer 2 · 2020-01-25T19:48:27.397

6

The HCMGIS plugin says it does this:

Spatial Processing: Create Skeleton/Medial Axis/ Centerline for road/ river networks and similar linear structures

Compatible with QGIS 3 and later; not compatible with QGIS 2.

edited Jan 25 '20 at 19:48

answered Apr 15 '19 at 17:30

csk

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Can you provide a link to that plugin, and perhaps mention the version(s) it works with? – PolyGeo Jan 24 '20 at 22:49
Just tested with QGIS 3.14 (Windows 7)--takes a little time on a complex network, but works well. – user25976 Sep 16 '20 at 02:32
Works really nice in v3.20. (use case: a single, linear polygon with moderately irregular boundary geometry) – CreekGeek Jul 12 '21 at 20:19
I'll add that this only adresses part of the answer...trimming of the skeleton is still required (per Step 4 on in https://gis.stackexchange.com/a/318733/17482) – CreekGeek Jul 12 '21 at 20:26
Be aware that there is a feature limit (100). – Alexander Gogl Sep 08 '22 at 13:50

score 3 · Answer 3 · answered Apr 14 '19 at 11:44

3

Try the GRASS algorithm v.centerline. You may have to tweak around with the parameters, but as long as your river polygons are longer than they are wide it should work for a large portion of your inputs.

answered Apr 14 '19 at 11:44

wfgeo

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Can you explain how to use it in QGIS? – MrXsquared Apr 14 '19 at 14:21
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@MrXsquared I am actually now surprised to find that this tool is not accessible from the Geoprocessing toolbox, so I guess my answer is not that appropriate to the question. – wfgeo Apr 14 '19 at 14:45

Creating centerline of river in QGIS?

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