### What is the focal length for computer generated pictures?

Hi there,

I am generated some rotated ArUco markers in MatLab and want to get the rotation as normal with OpenCV and C++.
The detection algorithm needs of course the camera matrix and the distortion model. The distortion model is easy to have for a perfect camera should be k1,k2,p1,p2,k3 = 0, am I right? The camera matrix offers me a bigger problem... what ist the focal length f (I assume fx=fy). I set the displacements zero: c=cx=cy=0. Now my Camera Matrix should be something like ~~that:
~~that:

M= [ f, 0, 0; ~~[ f, 0, 0
M= ~~0, f, ~~0
~~0; 0, 0, ~~1]
~~1]

Can anybody tell me, what focal length should be used?
In meanwhile I tried to calibrate it with a perfect picture of the (in my case) CharUco Board. (For the CharUco board is an additional avg_reprojection_error, I guess this should be also 0?)

I hope you can help me :)
Greetings ~~Sarah ~~Sarah