Study on the Algorithm of Quick Select Satellite in Beidou／GPS Dual-mode Positioning

     With the continuous development of satellite navigation, following the US government first realized the GPS global positioning system, China has also developed independent intellectual property rights of the Beidou navigation system.The emergence of different satellite navigation systems makes it possible to use dualsystem integrated navigation and positioning.Using a dual system combination positioning mode, the navigation receiver can receive more than 20 visible stars at the same time, which greatly increases the number of visible stars, providing a very precise positioning.But the number of visible satellites increased significantly to bring positioning accuracy at the same time also brought a lot of calculation, coupled with the actual operation of some of the problems, have greatly increased the election time.Based on the relationship between GDOP and constellation geometric layout, this paper proposes a satellites selection algorithm based on elevation and azimuth.The method is based on the requirement of positioning and filter based on the elevation of visible satellite, reasonable choice of different elevation satellites, follow the principle of uniform satellite distribution, will be find an effective positioning balance in the ideal situation and the actual situation, to avoid the ineffective selection of satellites and reduce the amount of computation, thus greatly reducing the satellite selection time.This method effectively achieved quick selecting satellite in Beidou／GPS Dualmode Positioning