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Strange problem - Bent roadway

I am flying a roadway for final volume calculations.  The initial processing was successful.  The graphic show a huge problem in the vertical solution.  I have not added the GCP yet.  It showed a camera error of 1.9% so I am reprocessing now.  I will add the G


CP and see if it straightens this out.  But it sure looks weird.

I opitimized the cameras and ran the project again.  This time I still have a 1.95% camera error but the project looks much better.

  I will now add gcp and hopefully the issue is not important.

Often default settings don’t work in Pix4D so experimentation is needed to get the best results (and staying out of the cloud)…and yes GCPs are almost always needed on narrow corridor mapping or you get twist and bow.

Thanks for posting updates William. 

My two main recommendations for long corridors are: 

  • split the corridor into smaller bits that have overlap between each other and merge them afterwards. This reduces the error propagation and should improve the calibration of the images in the first step.

  • add GCPs, these can help the merging procedure as well and should also reduce the curvature, I agree on that with Adam. 

I can recommend this article on the subject: https://support.pix4d.com/hc/en-us/articles/204909679

Thanks for the support.  This is actually part 3 of a much larger project.  With GCP the project looks fine.  We always use GCP and we put extra points on both sides of the corridor for the overlap area.  We make the overlap area more than 1000’ long with 6-8 extra GCP.  We also profiled the roadway with a vehicle as a rough check  and we are very happy with the resuls.  We do lots of corridors for volume measurement, pre and post construction.  I have probably done 30+ projects and have never seen one process like this before.  

One problem noted in the processing was the Absolute Geolocation Variance was really large in the Y value ( +250’).  The other two phases of the project were all less than 10’  for the X and Y values.  Elevation differences are usually large but usually consistent between phases of a project.  I believe that this would have to be a problem with the EXIF from the drone.  

We have saved some contractors a  lot of money on  several projects by having accurate topography when there is a dispute over volumes.  After catching a volume error worth several million dollars, the contractors are much more willing in invest in using this service.

Again, thanks for your support.