Adjust Project elevation in place

[dpitman]

Maybe I'm missing something and would appreciate a hand-hold.  I have a project created from dji drone images.  We all know the elevation is not correct in the image exif and there are workarounds to try and fix that.  But what about simply adjusting the elevation of the entire project?

For example.  When you export a Dense Cloud, or a surface mesh, you are presented with a dialog where you can adjust XYZ coordinates on the exported file.  If you import a cloud or model you can also apply an adjustment. 

I cannot find a way to simply make that same adjustment to the project in place.  Doesn't it make sense that if the software can adjust the project on export or import that it should be able to adjust it in the workspace?

Maybe you can and I have not found it yet?

Also, I've noticed that if I ADD a distance in the Z (A) field, it actually moves the exported model in the oposite direction, that is, the elevation of the model gets lower.  If I use a negative value (-100) it will raise the model 100 meters.  This seems counter intuitive to me but maybe that is the way it should be?

Thanks!

Dave

[Alexey Pasumansky]

Hello Dave,

The values input to Shift fields are being subtracted from XYZ coordinates of the exported point cloud. So if you input negative value it will be subtracted, i.e. absolute value will be added.

As for the "in place modification" of the project, adding the same value to altitude for all the reference points (cameras and markers) in the Reference pane should be correct approach (an example of such implementation applied to the cameras is add_altitude script: https://github.com/agisoft-llc/metashape-scripts/blob/master/src/add_altitude_to_reference.py).

Moving only mesh or dense cloud by fixed Z value doesn't seem to be a proper way, as all other chunk elements will remain in their initial locations and further processing operations would lead to the invalid results.

The mentioned script can be adjusted for your needs, if you describe in some additional details, which common task you need to solve.

[dpitman]

Hi Alexey,

Thank you for the explanation. I will investigate the script. 

Would another way to accomplish this be to insert a marker on a location for which I know the general elevation and then un-check all the cameras before processing the dense cloud or mesh? Would this method also result in the processor ignoring the image exif values and align the model according to the marker elevation?  Or would that result in unintended degradation, like warping, because there is only a single marker?

By doing this, I'm not trying to make the surface "survey accurate", but simply make it "close" to what I know the real surface to be.  These projects don't include surveyed GCPs.

Thanks again,
Dave

[Paulo]

Hi Dave,

I think you would need to place at least 3 markers at your suposed general elevation and then use Update Transform in reference pane (with cameras unchecked and markers checked) so that your cloud would be at the new supposed elevation and image centers will be accordingly shifted. An easier way is just note the actual elevation Z_ae of a point on the ground and calculate  the difference with the supposed elevation Z_se and just apply this difference DelZ = Z_se - Z_ae in above mentioned script and that will do the  trick (after doing Update Transform).

[dpitman]

Hi Paul,

That is what I thought regarding using a single marker.  I've just tried the script method and it seems to do what I was looking for. 

I always appreciate your input, thank you.

Dave