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Author Topic: Deformation Curved Terrain  (Read 6314 times)

matko

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Deformation Curved Terrain
« on: November 11, 2019, 03:15:10 PM »
Hello, I'm new at this.

I did a 1km x 500m survey with a DJI-Phantom 3 Pro, and when processing the information with Agisoft-Metashape it generates a DEM I have problems in altimetry, it describes a curved terrain of up to 10m of altimetric differences, when in fact the terrain is very flat and the height differences do not exceed 1m.

I think the error is in the calibration of the lens, I tried recalibrating and reconfiguring but I have no improvements.

How could I do to improve it?
Thank you very much, Regards!

Alexey Pasumansky

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Re: Deformation Curved Terrain
« Reply #1 on: November 11, 2019, 05:39:16 PM »
Hello matko,

Do you have GPCs in this project and whether you are performing the optimization procedure?

Can you share the screenshots of initial and adjusted values tab of the camera calibration dialog and the overview of the curved surface?
Best regards,
Alexey Pasumansky,
Agisoft LLC

matko

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Re: Deformation Curved Terrain
« Reply #2 on: November 13, 2019, 04:50:33 PM »
Thanks Alexey, I couldn't see where the previous messages were, I will detail you:

- The first processing I did without GCP, to visualize the data, you can see that it deforms the terrain but it seems normal to me since there is no control.

- The second processing I did filtering some photos that were not of good quality and worsened the final results.

- The third processing I did with GCP and you can see that the results improve somewhat but not enough.

After this I began to investigate the details of the lens and the camera and I made new tests, in: tools \ lens \ calibrate lens ...
and then in tools \ camera calibration ... I can see that it recognizes the characteristics of the camera (FC300X [3.61mm]).

- In the tests I did using:
«Camera Calibration / Rolling-Shutter Compensation» [on]
«Camera / GPS / INS offset calibration» Enable Reference [on]
«Camera / GPS / INS offset calibration» Adjust GPS / INS offset [on]

The results change but not for the better ...
I also tried «Tools» / Optimize Cameras ...

I was reading about these types of problems and what I could find are articles like this:
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2011JF002289
That suggest changes for improvements but since the Survey, which I can't do now. I would like to know if I can take advantage of my data

Спасибо большое!

Shipment attached screenshots:

wizprod

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Re: Deformation Curved Terrain
« Reply #3 on: November 14, 2019, 07:22:53 PM »
How trustworthy are your GCP-locations?

How does your flightpattern look?

matko

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Re: Deformation Curved Terrain
« Reply #4 on: November 14, 2019, 08:09:41 PM »
Hi wizprod, the GCP accuracy is below 5cm for all cases, it is quite good for the tolerance of my work. As for the flight pattern attached a capture from Agisoft:

matko

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Re: Deformation Curved Terrain
« Reply #5 on: November 19, 2019, 07:33:45 PM »
How about Friends: unfortunately I have not been able to resolve this issue since processing, apparently there is no camera model that allows me to correct the curvature effect.
I will opt for a polynomial interpolator that allows me to correct the already generated dsm.
Thank you for your contributions.
Regards

bgroff

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Re: Deformation Curved Terrain
« Reply #6 on: November 21, 2019, 09:29:13 PM »
Hi Matko. The curved terrain, in my experience, is directly related to camera calibration. I started with a Phantom 4 Pro and discovered that there are a number of camera settings in the DJI software that must be set prior to the flight to have a successful outcome. Also, fixed calibration parameters in Agisoft are very helpful. See a prior post here on our calibration method:

https://www.agisoft.com/forum/index.php?topic=10451.msg47539#msg47539

For DJI camera settings, we use a focus setting of infinity, 1/800 shutter speed and shutter controlled camera settings (i.e. ISO and f-stop are shutter controlled). White balance is generally set to sunny or cloudy, and not automatic. We also use a CP lens filter most of the time, except when it's very cloudy.

A lot of problems were resolved after we set the camera parameters. As far as GCP, I try to have a GCP at least every 600 ft to maintain control of the survey.

wizprod

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Re: Deformation Curved Terrain
« Reply #7 on: November 24, 2019, 01:17:11 PM »
How many GCP's are you using?
What are their pattern of distribution?
Can you also share a screenshot of your Markers window?