Better documentation for Camera Intrinsics and Distortion parameters.

[TommasoBendinelli]

Hello,
I have just stumbled into these file: https://github.com/zivid/zivid-python/blob/master/modules/zivid/camera_intrinsics.py
Camera Instrinsics and Distortion parameters are quite useful for a lot of applications and should be documented better.

Best

[eskaur]

Hi!

First of all, if you are wondering how to retrieve intrinsics from a camera, look here:
https://github.com/zivid/zivid-python/blob/master/modules/zivid/experimental/calibration.py

If you are looking for documentation on how to interpret the values, then I agree it could be better. Long story short, it is the "Standard OpenCV model" intrinsics:
https://docs.opencv.org/4.x/dc/dbb/tutorial_py_calibration.html

[TommasoBendinelli]

I tried to match the parameters got from Zivid calibration.py against the one I have obtained with CalibrateCamera from OpenCV and the parameter values are completely different. Are unit of measurements different somehow?

[diviz-imas]

Hi Tommaso!

There should be no difference in units. The Brown distortion model uses unitless parameters that work in normalized coordinates.

Can you share the two sets of parameters for reference?

[TommasoBendinelli]

Actually, it was an issue on my side. Sorry about that. I made a small bug in the code, which resulted in wrong values.
Now my values and the ones from Zivid SDK are much closer:
Zivid:
{"_k1": -0.08929276466369629, "_k2": 0.11623617261648178, "_k3": -0.03393297642469406, "_p1": -0.0004479888884816319, "_p2": -0.00011812106822617352, "_cx": 969.7472534179688, "_cy": 592.1499633789062, "_fx": 1778.913330078125, "_fy": 1778.9261474609375}
OpenCV:
{"_k1": -0.07816818141757419, "_k2": 0.06866144436678583, "_k3": -0.024689114436057036, "_p1": 0.00016911156978288228, "_p2": -0.0004692102909033517, "_cx": 959.6700426181453, "_cy": 592.86066030548, "_fx": 1,776.7353645734295, "_fy": 1,779.8388818694884}

How are the Zivid values computed? Are these parameters uniquely computed for each Zivid camera you produce, or are they fixed for all Zivid II cameras? I am wondering whether I should trust the ones obtained from the Zivid SDK more, or the ones that I compute via calibration. Thanks!

[diviz-imas]

All Zivid cameras are individually calibrated over a wide range of temperatures and aperture values with a high-end calibration process and custom algorithms. My recommendation is to trust the ones from Zivid SDK.

[TommasoBendinelli]

Thanks for this relevant info! It would make sense to add it into the documentation

[diviz-imas]

Thanks for the feedback Tommaso. We'll see what we can do to improve the docs.