GPS,GLONASS,BDS联合伪距单点定位。包含各系统的卫星位置计算和最终的联合平差，有详细注释-GPS,GLONASS,BDS singel point position

通过北斗导航电文数据，计算BDS卫星坐标，存入矩阵，输出结果包括北斗卫星编号，北斗笛卡尔坐标，钟差，时间(BDS satellite coordinates are calculated by Beidou navigation message data and stored in matrix. The output results include Beidou satellite number, Beidou Cartesian coordinate, clock difference an