Generated DEM/Surface not consistent with Point Cloud

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

The last couple of quality control checks on my last two projects have both had the same issue where the elevations on the point cloud are spot on. But when created a dxf or geotif of the surface (DEM) the export has serious issues. I check the cloud against my survey data to find all are spot on. But, when I generate the DEM (dxf to geotif, doesn’t seem to matter) there are errors.

My most recent had all my GCPs and check points perfect. However one of the GCP’s was 10m lower in the DEM than in the point cloud. This was in a clear cut forest area with no trees and the odd bit of ground growth.

Last week on another project where all the ground had been stripped to rock had similar issues. The point cloud was again perfect. But after the DEM generation was 3-4m out in the vertical.

It took a great deal of time to identify the issue and get it resolved. In the meantime I am bring the point cloud into Autodesk Infraworks and using that to generate my terrain surface which is producing excellent results. From there I can use in C3D.

Has anyone else had this issue or is there a solution?

2

Hi,

In Pix4Dmapper, we have a vertical offset issue. More about this problem here. Could you please verify whether using 4.5.6 solves the problem? If not, please attach here your Quality Report.

Thank you in advance.

Regards

3

Hi,

Here’s the report. As mentioned the point cloud checked out perfect. Only on creation of the DEM did things go wrong.

Cheers

WH Stage 8 Jan 5_report.pdf (1.5 MB)

4

This was the second project where the point cloud was accurate. Then on my check in the DEM all survey checks were good with the exception of my southern most GCP which resulted in the DEM having an elevation 10m lower than the GCP.9951 West Coast Road jan 5 21_report.pdf (2.6 MB)

5

Hi @civil,

Thank you for your analysis.

Could you verify whether the same happens when you use 4.5.6?

I would be very grateful for your help.

Regards