用卡尔曼滤波法，虽然刚开始的初始高度协方差很大为100，但通过2步之后减小到不超过1，逐渐接近于0-Kalman filtering method, although the beginning of the initial height of 100 covariance great, but by following the two-step reduced to no more than 1, and gradually close to 0