calibration + posit for z distance measurement?

edit

Can anyone suggest if I'm headed down the right direction? I'm trying to find a way to calculate the distance from the camera of a chessboard pattern. From what I've been able to figure out I can calibrate the camera and get camera intrinsics, then use those with known physical object points (knowing the actual physical size of the chessboard squares). It seems like I could use POSIT to get the positions of the square corners. Would that work? Is there an easier way that I am overlooking? My goal is to take a picture of a chessboard and figure out the distance from the camera. or the average distance for the square corners