在惯导系统进行粗对准之后，惯导平台和当地导航坐标系之间还存在一定偏差，此时基于粗对准的结果，利用以速度为观测量的Kalman滤波对姿态进行估计
aligni0vn函数为精对准主函数
/* SINS initial align based on inertial-frame & vn-meas method function -----------------------------------------------------------
* initial align
* args : struct imut I imu structure
* struct imuerr I imuerr structure
* struct kf I kf structure
* double pos I position information of initial time
* double rk I velocity measurement noise (3x1 vector)
* double t1 I inertial-frame align time
* return : kf structure
*-----------------------------------------------------------------------------*/
extern double* alignvn