Point Cloud Ground Control Points heights Accuracy

Answered

August 06, 2019 20:33

Hello

I am trying to use CR for Stock pile Quarry volumes and I am having issues with Height Accuracy. I use a DJI Phantom 4 Pro. I have brought the GPS Images in and also Ground Survey Ground Control Points in and chosen the Points and then re-aligned and then ran the processing.

But the Heights aren't the same as my CGP Points I bring In.

One of My GCP's as i have imported it.

1 CROSS6MM,407786.3600,348541.3960,290.78400 ( Height Being 290.78400)

The Eastings and nothings seem to be correct just the height is a problem.

I have tried to not use the Exif data from the images from the drone but that seems to only make a slight difference.

But I then export the point cloud to a 3rd Party software N4ce and the highest point is only 200 Metres in the image below the e: 117.76m I assume is what it thinks as the height although I have told it to be 290.784.

Am I doing something wrong on the workflow somewhere. I would be really so glad for any help that anyone can point me in the direction of.

Is anyone using the point cloud for stockpile volumes and getting the required accuracy ?

Thank you very much

Rob Grain

Comments

5 comments

Jakub Vanko RC

August 07, 2019 06:45
Hi Robert,

try turning off camera priors in the alignment settings and align again. This will ignore georeference from the cameras and only use GCPs. After this your GCP errors should be much lower and not around 110 m.
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Robert P Grain

August 07, 2019 19:45
Hello

Thank you very much for the help.

I have just tried that but sadly it is still doing the same. I don't quite understand why it would do this either to show the z error of -100,000,

When I create the GCP it shows correctly and then as soon as I add images then it starts to show wrong data so I assume I am bringing in the file correctly because it shows the correct location in the map.

I think I must be so close it is just this one last thing stopping me getting my results. I assume it must be possible ?

Thank you

Rob Grain
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Jakub Vanko RC

August 08, 2019 07:26

Edited
If you used the previous alignment you need to also set Force component rematch to True. It is in the Alignment settings, Advanced. It should definitely work with the Camera priors set to False this time. Please let me know if it worked for you.

Jakub
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Robert P Grain

August 27, 2019 19:54

Edited
Hello Jakub

I'm sorry for the delay in replying. I have now got the accuracy working well thanks to you, It works really well now I have turned the UAV GPS points off with the Exif =False and the Camera Priors = False.

However I have found that to make it search through the images to help identify the Images that the Ground Control Points are in I run an alignment first with the GPS from the UAV and the Priors on = True, Then add the ground control points and then it helps identify the other images my points are then in and then I turn the Priors off and the Exif's to False and run the Alignment again,

I have gone from being a long way different from the Ground Survey Equipment to within 5% of them and so now I can tell clients that I am happy with the results I am getting is a true figure.

Thank you very much for your help and support

I love this software.

Rob Grain
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Jakub Vanko RC

August 28, 2019 06:42
Hello Robert,

I am glad my answer helped you. You are doing it excatly how it should be done. To save time you can just do a draft alignment with the camera priors instead of full alignment. Then you approximately place your GCPs on the point cloud in the 3D view and refine their positions in images in the 2D view and do a full realignment again. Good luck with your future projects.

Jakub
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