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rameau-fr / MC-Calib

A generic and robust calibration toolbox for multi-camera systems
MIT License
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Fisheye distortion coefficient format #68

Closed shreyas23 closed 6 months ago

shreyas23 commented 6 months ago

Hey @rameau-fr hope you're doing well!

I'm calibrating a set of fisheye cameras and initializing K with some nominal known values while setting the distortion coefficients to 0. I noticed that k4 is always 0 after optimization.

After brief investigation it seems like there's a discrepancy in the format and order of the distortion vector:

via OpenCV in fisheye::calibrate() : Output vector of distortion coefficients (k1, k2, k3, k4).

https://github.com/rameau-fr/MC-Calib/blob/0f893aa86e1cef4f5c41632713d660e62c42819d/McCalib/include/Camera.hpp#L43 setDistortionVector: https://github.com/rameau-fr/MC-Calib/blob/0f893aa86e1cef4f5c41632713d660e62c42819d/McCalib/src/Camera.cpp#L59-L63 getDistortionVector: https://github.com/rameau-fr/MC-Calib/blob/0f893aa86e1cef4f5c41632713d660e62c42819d/McCalib/src/Camera.cpp#L85-L90

but then during optimization: https://github.com/rameau-fr/MC-Calib/blob/0f893aa86e1cef4f5c41632713d660e62c42819d/McCalib/include/OptimizationCeres.h#L67-L70

If I understand correctly, the following changes should be made:

setDistortionVector: intrinsics_[6] = distortion_vector.at<double>(2); intrinsics_[7] = distortion_vector.at<double>(3);

getDistortionVector: distortion_vector.at<double>(3) = intrinsics_[7]

Let me know if this sounds right to you.

rameau-fr commented 6 months ago

Hello @shreyas23, I do not know how to thank you enough for reporting it !! I think you are right. I will double-check this issue with @BAILOOL, and we will make the change as soon as possible. It is quite a big bug here. It might also be the reason why some persons calibrating large field-of-view cameras were facing issues during calibration. Please, keep me in touch if you make some tests with your modified version of the code.

shreyas23 commented 6 months ago

My pleasure! I did run some tests while fixing it on my end and seemingly had better convergence. I can run some comparisons when I get a chance but the effects likely aren't significant in my scenario as my FoV is not too high.