Issue calibrating fisheye camera (-215:Assertion failed) fabs(norm_u1) > 0 in function 'InitExtrinsics'

Hi all,
I am having issues calibrating my fisheye camera. This does not occur all the time (or with all cameras/images I have) but it still prevents me from calibrating my cameras. When calling the calibrate function, I get the following error:

line 91, in calibrate
    err, K, dist, _, _ = cv2.fisheye.calibrate(objpoints,
cv2.error: OpenCV(4.5.5) /io/opencv/modules/calib3d/src/fisheye.cpp:1400: error: (-215:Assertion failed) fabs(norm_u1) > 0 in function 'InitExtrinsics'

I read somewhere that this could have to do with some corners being too close to the image borders but I don’t get why that should be the case. When using another camera model (not fisheye) I do not encounter any problems.

I get around this error if I remove the cv2.fisheye.CALIB_RECOMPUTE_EXTRINSIC flag but this is of course no solution.

Would be great if somebody can help me or explain to me what the error message actually means.

Thank you in advance!

if you still need to solve this, I would suggest digging into the opencv source at the given location (modules/calib3d/src/fisheye.cpp:1400).

it’s checking some numerical properties there. you’d wanna follow this u1 thing upwards.