I found many posts here but no one was the solution for my problem. I would like to: 1.) digitalize forest roads, 2.) extract slope values from an underlying DEM, 3.) divide the roads into segments, 4.)color the segments according to their slope (see picture below. for example blue = slope 0-5%, yellow = 5-10%, violet = 15-20%, orange = 10-15%)

enter image description here

I would like to segment the polyline with kind of "terrain-based segmentation" where a segment is made where slope changes from one slope category into another. I also would like to assign this segments automatically to a slope category.

I am aware that there are many tools to segment lines.

Extracting the underlying elevation values is also not a problem (with extract or point sampling tools) but how to assign these values to a line and color it according to these values?

This approach (How do I find the slope of road segments with point elevation data of the same linear path) is good, but not working for QGis unfortunately.

  • Do you have attribute information for each line segment that pass through the terrain with an associated slope value? – whyzar Oct 4 '17 at 18:46
  • I don't have line segments yet. This was part of my question, how to create them... – Quarantäne Oct 4 '17 at 20:04
  • You'll probably get more useful answers if you split this into separate questions. – csk Oct 6 '17 at 17:46
  • How to go about digitizing forest roads depends on what source data is available for your area. If there already exists a vector layer of roads for the area, all you need to do is filter it to the forest roads. If you have a paper map, you could scan and georeference it, then manually digitize the roads. Or manually digitize them from satellite imagery. – csk Oct 6 '17 at 17:53

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