On calibrating a camera network using parabolic trajectories of a bouncing ball

Camera networks are often used in visual surveillance systems for wide-range monitoring. In this paper, we present a novel method for calibrating a camera network, which uses the trajectory of a bouncing ball as the calibration data. An important feature of our method is the use of the parabolic property of a ball's bouncing trajectory. This parabolic trajectory will lie on a plane, called the parabolic trajectory plane (PT-plane), so that the relationship between the trajectory's points and their corresponding image points is a homography. Combining the vertical velocity determined by the earth's gravity and the horizontal velocity calculated from the homography, we can compute the 2D coordinates of the trajectory points on the PT-plane. By throwing the ball multiple times, we obtain calibration points on multiple planes for calibrating both intrinsic and extrinsic parameters of the networked cameras. Experimental results have demonstrated the feasibility and accuracy of the proposed method.