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DXF file DTM Contours


I have picked the option to export a DXF file DTM contours from Pix4dmapper in processing option 3. When I looked at the DXF file output the top of the building and shrubs have contours. So I then deleted areas in the point cloud in the top right corner for my clients data within Pix4dmapper and rerun process 3.
The area is a light industrial area with lots of structures. I have attached a image of the area with the contours overlayed. In the top right corner the contours of the image the contours are correct after I deleted the areas over the building and shrubs no contours on top of the buildings. In other areas contours are the top of the buildings.
Would someone please explain why this is happening and if it is a problem with the processing in Pix4dmapper?
Correct me if I am wrong but a DTM should only export contours for the ground surface???

Please look at the screen shot of the DTM from Pix4dmapper, the top of the buildings are red.
Screen capture below of the settings for my contours output in process 3.
Screen shot of the area were i deleted the points cloud so I could get the correct DTM contours…


Regarding the contours including above-ground objects, this is due to the DTM not having removed all the appropriate objects.
The reason is that the point cloud was not correctly classified. So you probably have to edit the point cloud and move all the unwanted points in the point cloud to the disabled layer.

Hence I would recommend the following:

  1. Save a copy of your project with Project > Save as with another name. It is common to perform operations to get the best DSM possible in a separate project because the changes are quite extensive and will have an impact on step 2 and 3 outputs you may be interested in.
  2. Assign all points or areas that you would not like to be included in the DSM and DTM to the Disabled point group.
  3. Click Project > Save .
  4. Process step 3 to generate the DTM. Learn more about the DTM and which areas are included in it HERE.