GPS定位中调用的选星子程序，依据每颗卫星贡献的GDOP值的大小进行选星，其中又分为递推选星和直接选星。考虑到机动载体存储空间限制，选星为4颗或6颗。而6颗卫星的GDOP值更接近所有卫星时的值，且计算量小。-GPS positioning called planetesimals selection process, based on the contribution of each satellite GDOP value of the selected size of stars, whic