Implementation of Kannala-Brandt camera model

[TheRealKaufmann]

Hi there,

I really like this project! Since this code only supports the Fisheye Camera Model, I was wondering if it is possible to implement the more generic Kannala-Brandt Camera Model?
I am trying to get this to work with a stereo 160 degree fisheye camera (Intel T265) but it does not seem that it can be calibrated with the Fisheye Model.
So what would have to be done (key points) to implement the Kannala-Brandt Model?

Thanks,
Tom