In our voxl-camera-server, we have a default intrinsics config for the IMX412 camera / lens as follows (focal length approximation is based on a several calibrations). Basically it is a fisheye lens with about 2000px focal length at full resolution (half of that at half resolution, etc). The camera full sensor width is 4056 (hence the x principal point is exactly half of that 2028). In some cases we use slightly trimmed frame (4040 in width). But in any case, that should be enough for a good starting point.

lens_cal.width  = 4040;
lens_cal.height = 3040;
lens_cal.fx     = 1999.0;
lens_cal.fy     = 1999.0;
lens_cal.cx     = 2028.0;
lens_cal.cy     = 1520.0;
lens_cal.is_fisheye = 1;

Alex