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Author Topic: Detect Marker Issue or Tie Point Discrepancy issue?  (Read 2658 times)

BenW22

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Detect Marker Issue or Tie Point Discrepancy issue?
« on: October 12, 2024, 11:10:06 AM »
Hi All,

I'm  using MS Pro v2.1.3.

I have carried out a UAV flight with a DJI M300 and P1 camera of a pedestrian foot bridge. I have flown nadir and oblique flights and also captured images with a Canon hand held camera. Prior to the flight we placed many black and white targets on the bridge.

After aligning the images using highest accuracy setting and then running the detect targets command, Metashape has picked the centre of many targets correctly. Metashape allocated Marker numbers for those targets.  I have noticed that Marker No 6 has been correctly identified (center of target correctly picked) in 36 images. I also notice that Marker No 14 has been correctly identified in 13 images. The problem is the target is the same target! Marker 7 and Marker 11 are about  15cm apart.

The images Metashape has picked the centre for Marker 6 are different to the images Metashape has picked the centre of Marker 14.  So for Marker 6, the marker is centered on the target in its images. And the  Marker 14, the marker is centered on the target in its images. How can this be?

In the Reference Tab  Markers list the difference is shown "View Estimated" Table  -
point 14   355681.7410382535   6308320.882072767   3.6456287776534353         13   
point 6   355681.8124383928   6308320.808663793   3.7618934840380938         36   

Does this mean the photos have not aligned correctly and Metashape thinks there a two targets in that area even though there is only one target there?  The detect marker settings were "Tolerance"  = 1 and " Maximum Residual (pix)" = 5.

Does this also mean there is Tie Point Discrepancy in the sparse cloud in that area?  If that is the case, I would have never have found this if I didn't have a target there. How could I have identify this issue with no target? It would also suggest there could be issues in other areas but I would not know until I have created a model or point cloud and could see the issue.

Please see attachment showing the issue

Any help appreciated

Kind Regards
Ben



BenW22

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Re: Detect Marker Issue or Tie Point Discrepancy issue?
« Reply #1 on: October 21, 2024, 03:57:54 AM »
Hi All,

I have had the same issue but with another project. Please see attached pdf.
Could anyone suggest why this is happening and give a possible solution?

Kind Regards
Ben

P.s. in my original post on the 12/10/24, the line "Marker 7 and Marker 11 are about  15cm apart." Should have said "Marker 6 and Marker 14 are about  15cm apart."