Support Website Contact Support Blog

DTM Wrong Values

Hi,
I have a curiosos situation here. A project with 512 pictures, grid flight. More than 20 GCP have done with GNSS, and area geoid ondulation of -6.29 meters.
After done all processing steps, I checked in Pix4D the DTM values, and got excelent position (X,Y) and altimetric (Z) value. Projection system was UTM Sirgas 2000 24S (EPSG 31984).

But, I needed to calculated slope, using ArcGis, and for my surprise, DTM valeus in this, were not same of Pix4D. I got DTM, inside Pix4D project, and copy to ArcGis project.

SO, why this difference between Pix4D DTM screen value and ArcGis? I have opend same DTM in Global Mapper, and got same difference. Is any problem in output vertical coordinate system definition? How can fixed it?

Thanks

Hera are two images.
First, from Pix4D, Z value is 56,04 meters.
Second, when image and DTM are opened in GlobalMapper, Z value is 46,10meters.

Anybody knows what´s is this problem?
GlobalMapper

Thanks

Hi @alealbuquerque

PIX4Dmapper does not support local vertical coordinate systems. You can find more information about that and workarounds here: When to use the Geoid Height Above the Ellipsoid Function? – Support.

Another solution is to look into PIX4Dmatic which does support local geoids: How to use vertical coordinate systems and geoids in PIX4Dmatic – Support. There is a 15-day trial that you could try out.

Best

Dear Rhea Garratt

This is not about geoid or ellipsoid functions.
The final DTM and Orthomosaic in Pix4D, both area right. I used output coordinate system as described in image. Have GCP, with orthometric Z value, and used the difference between the geoid and the WGS84 ellipsoid.

The problem is: why in Pix4D I have a Z DTM value in some point, and when I open the same DTM in ArcGis, Global Mapper ou Qgis, this point has other Z value.
Is like the pictures I have sent, In pix4D the white cross (isa GCP) has 56,04 meters and 46,10 meters in Globall Mapper or ArcGis
Is the same DTM file. DTM gerenated from Pix4D and opened in other software. So, why this difference from each one?

Thanks
Pix4D2

Hi @alealbuquerque

Thanks for the additional information and indicating the shift between geoid and ellipsoid is indeed one of the workarounds available in PIX4Dmapper to georeference results to a local geoid.

It is indeed unexpected for the coordinate of a feature to be different in PIX4Dmapper and third-party software.

A few questions for you:

  • Is the difference, the shift, the same across the extent of the whole area/file?
  • Could you send us the file so that we could have a look ourselves?
  • Could you provide the quality report for this PIX4Dmapper project?

Thanks