-240] [0 0 1] Which yields: [320*1 + 1*-320] [0] [240*1 + 1*-240] = [0] [ 1*1 ] [1] You'll recognize the above as the identity matrix with the displacement coordinates slapped in the upper-right corner. That's why the 1 (the "homogenous coordinate") is necessary: to make room for these coordinates,