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Author Topic: 1.6.4 DJI Phantom 4 RTK incorrect camera parameter  (Read 1763 times)

space111

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1.6.4 DJI Phantom 4 RTK incorrect camera parameter
« on: September 04, 2020, 08:12:56 AM »
When load DJI Phantom 4 RTK (FC6310R) image into metashape 1.6.4, the following camera parameters are incorrect :   F, P1, P2

For example :

when open an image through "notepad", camera parameter can be found
   drone-dji:DewarpData=" 2019-08-17;3682.980000000000,3676.280000000000,-9.900000000000,-2.550000000000,-0.263183000000,0.113290000000,0.001035960000,-0.000173821000,-0.041476400000"

The format of these parameters is as follows:
Calibrate_date;fx,fy,cx,cy,k1,k2,p1,p2,k3

"f" should be  (fx+fy)/2 , in current version, f value is incorrect
P1 P2 was correct in version 1.6.2,  however,these  values are reversed in 1.6.4

Thank you.


Alexey Pasumansky

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Re: 1.6.4 DJI Phantom 4 RTK incorrect camera parameter
« Reply #1 on: September 11, 2020, 10:13:16 PM »
Hello space111,

Can you please provide any sample image, so that we could check the meta information and the calibration data loading process?
Best regards,
Alexey Pasumansky,
Agisoft LLC

space111

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Re: 1.6.4 DJI Phantom 4 RTK incorrect camera parameter
« Reply #2 on: September 12, 2020, 01:52:59 PM »
Hi Alexey

here's the link that contains a sample image
https://mega.nz/file/QtEVHSYC#82eAcwl-44qylRUxS-84YHOOaE7aT9hmcJ61NX2PPAk

Best regards.

Alexey Pasumansky

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Re: 1.6.4 DJI Phantom 4 RTK incorrect camera parameter
« Reply #3 on: September 12, 2020, 09:57:20 PM »
Hello space111,

The order of P1 and P2 coefficients is different in the camera model used by DJI (https://docs.opencv.org/3.0-beta/doc/py_tutorials/py_calib3d/py_calibration/py_calibration.html) and by Metashape (https://www.agisoft.com/pdf/metashape-pro_1_6_en.pdf, see Appendix C), therefore the latest release fixes this inconsistency.

As for the focal length, in some older versions Fx has been used to calculate B1 parameter as Fx - Fy, whereas F was equal to Fy. However, based on our experience with different DJI sets, the value of B1 calculated in such way was too large (compared to autocalibrated values) and we decided to switch off B1 (Fx) extraction from the meta-information for DJI cameras.
Best regards,
Alexey Pasumansky,
Agisoft LLC