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Using grassGIS I am attempting to produce a DTM (remove buildings and vegetation) from the las point cloud. Unfortunately the point cloud exported from dronedeploy.com does not distinguish first and last pulses so the method based on GrassGIS v.lidar.egdection does not work.

  • I need an alternative method/tool particularly for removing buildings?
  • Any recommendations to transform the z-values relative to the drone take-off location to absolute ones (e.g.: sea-level,..)?
Philipp R
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A Structure from Motion (SfM) derived surface is not the same as LiDAR and will always result in a digital elevation models (vegetation and buildings included). I am not familiar with the specific workflow in GRASS but in general a workflow would be to heads-up digitize your buildings and vegetated areas. Buffer the polygons slightly. Use a zonal statistics tool to populate the buffers with the descriptive statistic of your choice like the minimum elevation within the buffer. Convert the buffers to a raster that represents the elevations under the buildings, and use that raster to replace the values in your SfM surface.

GBG
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  • Thanks for the clarification. Digitizing is an option but removes a great deal of analytical opportunities (eg Tree or object height, etc). In the ‘lastools’. Documentation parameters are given to cater for drone based point clouds, although the documents do not mention SfM. I was hoping to get some insights on those parameters and a similar workflow (equivalent to ‘lasthis’ and ‘lasground’ in grass. – Philipp R Dec 04 '17 at 10:45