<p>In various sports, the motion information of athletes is often measured for monitoring and evaluation, and the direct use of common optical equipment to determine the position and orientation of moving objects according to geometric information in a scene has become an important research topic in image understanding. As many sports grounds have a center circle and halfway line, we propose an algorithm that first obtains constraints on the image of the circle center by using homography based on the geometric properties of the circle perimeter and corresponding circumferential angle. Then, the vanishing line is obtained from the image of the circle center and the complete circle image based on the pole-polar relation with respect to the camera internal parameters. By decomposing the circle image, the camera external parameters are obtained to determine the homography matrix from a spatial point to an image point. The camera at the edge of the moving field is calibrated according to the duality of the conic and homography matrices. Using the homography matrix between a point on the moving ground plane and the corresponding image point, the coordinates of the measured point can be recovered to estimate the pose (i.e., position and orientation) of a moving target.</p>