Is there a way to convert a digital surface model (DSM) to a digital elevation model (DEM) in QGIS?

Surface models contain lots of noise (e.g. trees, buildings) when I only want to show the ground. I currently have to manually delete individual objects using a masking layer, replacing null values with GDAL Fill NoData and then smooth out with a gaussian blur. This is very laborious.

  • What you're doing now we used to term 'bulldozing', flattening areas above the ground, it is very tedious. Where did the DSM come from? Was it generated by LiDAR? If you have the LAS you can derive a DEM using the LASTools (not free, not expensive) plugins for QGIS. You could also export to XYZ format suitable for LASTools then run LASGround to classify ground/non-ground and generate a DEM with LAS2DEM. The free (trial) version has limits; I think it puts a diagonal stripe into the DEM. You would need to consider if your time and effort is worth more than a LASTools license. – Michael Stimson Jul 18 '18 at 11:21
  • I would also like to add that I am in no way affiliated with LASTools but having used them (licensed) I can see that it would be a very easy way of solving your problem. There may be other alternatives to your situation without having to purchase extra software you may or may not use again, if nothing else comes up though you could have a go with the free version and see if the workflow suits your needs. – Michael Stimson Jul 18 '18 at 11:25
  • Thanks Michael - The DSM was produced via photogrammetry (DroneDeploy). DroneDeploy now offers generation of a DEM for an extra fee, but the costs soon stack up when a single project comprises multiple surveys. LASTools looks like a winner except for the price - unfortunately I don't do enough of this to justify the expense at this stage. Global Mapper is on my shopping list and I believe it can achieve the same as LASTools. For now, I think I'm stuck with my bulldozer unless anyone else can provide a simpler workflow than described in the original question? – James Jul 19 '18 at 6:49

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