Support Website Contact Support Blog

Point Cloud not aligned with Ortho and survey data.

We are attempting to merge conventional survey data with aerial data. The orthomosaic matches great (see the sidewalk, drainage structures and edge of pavement), however the point cloud, contours, etc… are shifted about 4 feet. The elevation is correct. There were multiple GCPs used throughout project from the conventional survey data. 

Please explain what could cause this issue.

Hi Clifton, 

It is hard to say why this happens. As a first step, could you share the quality report of the project? Ideally, comment with a link to the file on a file sharing service such as Google Drive or Dropbox.

Also, do you notice any noise or double layers in the densified point cloud? 

There is minimal noise in the point cloud and not double layers. 

We have also switched from the global shutter setting to “Linear Rolling Shutter” and we are still getting Projection Error Pixel of over 0.500 on all GCPs.
https://www.dropbox.com/s/52ys8dqumwk5o0x/Sam%20Ridley-%20Area%202_report.pdf?dl=0 

Thanks,
For you help,

Kevin

Thanks for sharing the quality report! 

The GCP accuracy value needs to be adapted if the project is in feet [ft]. The default value is 0.02 [m], which is 0.066 [ft]. If the value is not changed, the project has too high constraints which can result in slightly distorted projects. This should already reduce the shift in your project. The GCP accuracy can be changed in Project > GCP/MTP Manager…, there you can change the Horizontal and Vertical accuracies. 


Please post an update, and if the shift is still there a new version of the quality report. Thanks!

The shift is still there and appears to be the exact same.

https://www.dropbox.com/s/u8ctkt7n69w9xlv/Sam%20Ridley-%20Area%202_report%202-19-2018.pdf?dl=0

 

Thanks for the report. 

I’ve sent you an email to continue the investigation. I’ll post updates here if I have any. 

Could you please CC me on the email if possible. mclemorek@civicinc.com

 

Thanks,
Kevin.

Ok, I’ve added you in cc!

Kevin was able to troubleshoot the issue: "We have found the cause of the shift. When the .las file is brought into autocad it has to convert to a .pod file. During this process there was a shift due to US Survey Feet & International Feet. "

Does this mean that the Accuracy defintion of the GCPs do not change to match the units of the project?  It’s always in meters even though it says feet?

Hi Angela,

You will need to edit the unit in coordinate system definition in GCP/MTP manager. If you are uploading your GCPs in ft, change the unit to ft. However, you will need to edit the accuracy accordingly as Pierangelo described above.