Registration using geometry features for augmented reality in soccer

A flexible registration method for augmented reality in soccer based on the field marks is proposed in this paper. By exploiting the geometry relationship among the centre circle, halfway line and the centre mark of the soccer field, the images of the circular points are obtained from the image plane. From the conjugated circular points and the two points of intersection of the halfway line and the centre circle, the homography between the field plane in space and the image plane is calculated. Furthermore, with the constraints that the CCD camera skew is zero and the principle point passes through the image centre, a simple equation is deduced to calculate the intrinsic parameters of the camera. And finally, the camera external parameters are derived from the homography matrix. The registration method is tested using synthetic data and real images. The results show that the method is effective and robust.