DSM < DTM

PIX4Dmapper
1

Hi everyone,

I’m processing data from a quite flat peatland. The vegetation height is negligible now during winter in Europe. The problem here is the values in part of generated DTM are higher than DSM, i.e. DSM<DTM, which makes no sense in my knowledge.

Is there any suggestion? Thank you!

2

Hi,
did you tried to classify first your point cloud and later use ground points to generate the DTM?

  1. https://support.pix4d.com/hc/en-us/articles/115004864586-How-to-generate-the-point-cloud-classification

  2. https://support.pix4d.com/hc/en-us/articles/202560579-How-to-automatically-generate-a-Digital-Terrain-Model-DTM#gsctab=0

2 Likes
3

Hi,

Thanks for reponse! I did select point cloud classification. Everything is fine in forest area, but in flat area around 30% of pixels have higher DTM values compared to DSM…

4

Hi,

Could you make sure that the areas that you would like to keep in the DTM are classified as either ground or road surface? If not, please edit the point cloud classification (learn how here). To get the cleanest DTM possible for your project, I also recommend you deactivate all points corresponding to heights and areas you want ignored for the DTM. To do so, ensure the points are assigned to the “Deactivated” point group.
You can consider creating a copy of the project (Project > Save As…) before deactivating the points.
Then, generate a new DTM.

If this does not help, could you post a screenshot of the rayCloud?

  • Choose an area that has different values in the DSM and the DTM.
  • Make sure the dense point cloud is visible.
  • Take a screenshot of the side of your project, so that we can see the height of your points (not from the top).

Also, please attach your quality report, thanks!