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Author Topic: Obtaining a Camera Calibration  (Read 2810 times)

dpitman

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Obtaining a Camera Calibration
« on: September 26, 2020, 05:42:43 AM »
Hey guys, 

Some of the uas surface modeling I do uses ground control and results are reasonably accurate. I'm assuming that the camera optimization is inhanced due to the accuracy of the GCPs.

 I also have projects that do not use  ground control.  Is there a workflow to pull and save the camera corrections from the project with ground control and then be able to apply that correction to the cameras in other projects that used the same drone?

Thanks,
Dave
« Last Edit: September 26, 2020, 03:58:01 PM by dpitman »

JMR

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Re: Obtaining a Camera Calibration
« Reply #1 on: September 29, 2020, 11:01:00 AM »
Hi, Dave
Same drone means nothing I guess you mean same camera.
But how a camera can be the very same? the only case one can say so, it is when we are using metric cameras with lockable or nonexistent focusing mechanism, etc.
Using fixed (pre-calibrated) lens parameters does not necessarily come with better global accuracy unless camera positions are of high quality (few cm accurate).
That said, yes. It can be done. Export your parameters from the camera calibration dialogue while you are seeing the adjusted tab.
with the new uncontrolled project, before alignmente go to same dialog, import the camera calibration file, and set mode to pre-calibrated. (Also you can choose which parameters you want to set as fixed)... then align.
Regards,
GEOBIT

dpitman

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Re: Obtaining a Camera Calibration
« Reply #2 on: September 30, 2020, 06:15:41 AM »
Thanks for the reply, JMR.

Yes, in my case a P4P, so same drone = same camera.

Which parameters do I select in the dialog (screenshot below).  Are you saying that exporting these corrections and subsequently importing them in to another project will not be worth it?


I believe that Photoscan used to be able to generate a camera calibration with a checkerboard pattern.  Did this turn out to be of no value?  I think the P4RTK comes with a  lens calibration file and it is the same camera as the P4P.

Thanks again for the input.

JMR

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Re: Obtaining a Camera Calibration
« Reply #3 on: September 30, 2020, 07:18:11 PM »
Hi Dave:
These are not lens parameters or corrections, but reference data. And definitively they should not be used in a different project in any case.
If you want to export for re-use lens corrections, you need to export camera parameters from the camera calibration dialog.
Importing lens calibration that came out of a different project could make some sense with a P4P because its camera apparently (according to some papers I have read) is reasonably stable.
But for those parameters to be accurate and valuable for future cases, your source project needs to be very well constrained, which is not always the case with drones without an accurate camera geotagging system. It will depend on the ground texture, overlap, block geometry, etc. It is a complex question, Dave.
Calibrating by means of the Metashape's built-in checkerboard calibration feature is not a real alternative for drone cameras. It is intended for close range, unless you had a screen of the size of a football yard.
Best regards

dpitman

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Re: Obtaining a Camera Calibration
« Reply #4 on: October 02, 2020, 06:19:56 AM »
Thanks JMR, got it.  Would I use the "adjusted" #s in that dialog?