I am a forest engineer and I have to reclassify a DTM in upside pixels and downside ones in relation to a line shapefile indicating skid trails network of the forest parcels. I don't have necessarily to reclassify the DTM but I need to know and identify zones which have an higher altitude than the skid trails and zones which have lower one.

I am using QGIS.

  • Not sure I understand your question correctly. Do you want to know if the trails are going up or down? – nielsgerrits Aug 28 at 11:11
  • I think a good starting point would be to divide the trails into single-elevation sections. Create a Voronoi diagram around the trail sections (divide the entire area into polygons, where each polygon contains the area that's closer to the corresponding trail than to any other trail). Classify each polygon based on the elevation of its corresponding trail section. Then you can re-classify the DTM pixels based on whether their elevation is higher or lower than the polygon value. – csk Aug 28 at 17:13
  • At first thanks... no I only want to identify the zones with Higher or Lower altitude in relation to the trais in order to plan Wood extraction... I would try your method and then I will let you know if I would reach my aim – Francesco Latterini Aug 28 at 21:46

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