开源的GNSS导航定位包RTKLib的学习历程（一）RTKLIB简介：由日本东京海洋大学开发（Tokyo University of Marine Science and Technology），笔者查到最早的介绍是一篇日文的，《RTK-GPS用プログラムライブラリRTKLIBの開発?評価および応用》，其介绍的为RTKLIB ver.1.1。
另有一篇论文《Development of the lowcost RTK GPS receiver with an open source program package RTKLIB》也可以看下。
其主要功能如下：支持标准的GPS、GLONASS、QZSS和SBAS的为精确定位算法（目前此版本不支持Galileo系统）支持多种动态、静态卫星定位方式（单点定位、DGPS、载波相位动态差分定位RTK、静态、移动基站、PPP）支持全球定位导航系统的多种标准格式和协议支持多品牌接收机的专有消息传输协议支持多种通讯方式＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝华丽的分割线＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝下面开始介绍笔者的学习历程，由于工作的原因，时间跨度有些大，断断续续的。
初次接触RTKLib是在2010年8月份，当时版本还是2.3.0，下载了源码，花时间做了一个简单的应用：通过调用RTKLIB的API接口，进行单点定位，并计算出速度、方位角、仰角等，主要调用的函数依顺序为：init_raw，input_raw，pntpos，ecef2pos，pntvel，ecef2enu，free_raw 。
由于作者用Borland C++开发，笔者用的是VC++，所以移植时还有一些函数需要自己实现，如：int showmsg(char *format, ...)等。
注：pntvel在2.4.0发布时，已去掉。
应用时调用的主要函数接口如下：// initialize receiver raw data control struct and reallocate obsevation and// epheris buffer// args : raw_t *raw IO receiver raw data control struct// return : status (1:ok,0:memory allocation error) */extern int init_raw(raw_t *raw);// free receiver raw data control ----------------------------------------------// free observation and ephemeris buffer in receiver raw data control struct// args : raw_t *raw IO receiver raw data control struct// return : none//-----------------------------------------------------------------------------*/extern void free_raw(raw_t *raw);// input receiver raw data from stream -----------------------------------------// fetch next receiver raw data and input a message from stream// args : raw_t *raw IO receiver raw data control struct// int format I receiver raw data format (STRFMT_)// unsigned char data I stream data (1 byte)// return : status (-1: error message, 0: no message, 1: input observation data,// 2: input ephemeris, 3: input sbas message,// 9: input ion/utc parameter)// -----------------------------------------------------------------------------extern int input_raw(raw_t *raw, int format, unsigned char data);/// single-point positioning ----------------------------------------------------// compute receiver position, velocity, clock bias by single-point positioning // with pseudorange and doppler observables// args : obsd_t *obs I observation data// int n I number of observation data// nav_t *nav I navigation data// prcopt_t *opt I processing options// sol_t *sol IO solution// double *azel IO azimuth/elevation angle (rad) (NULL: no output) // ssat_t *ssat IO satellite status (NULL: no output)// char *msg O error message for error exit// return : status(1:ok,0:error)// -----------------------------------------------------------------------------*/extern int pntpos(const obsd_t *obs, int n, const nav_t *nav,const prcopt_t *opt, sol_t *sol, double *azel, ssat_t *ssat,char *msg);// velocity estimation by single-point positioning -----------------------------// compute receiver position/velocity and clock-bias/drift// args : obsd_t *obs I observation data records// int n I number of observation data records// nav_t *nav I navigation messages// double *rr I receiver position (ecef) (m)// double *azel I satellite azimuth/elevation angle (rad)// int *vsat I valid satellite flag// double *vr O estimated velocity (ecef) (m/s) (3 x 1)// double *Qv O estimated velocity covarience (3 x 3)// double *ddtr O estimated receiver clock-drift (s/s)// return : number of valid satellites (<0:error)// -1: number of valid dopplers, -2: least square error// -3: iteration divergent, -5: validation error,// -6: gdop error// -----------------------------------------------------------------------------*/extern int pntvel(const obsd_t *obs, int n, const nav_t *nav, const double *rr, const double *azel, const int *vsat, double *vr, double *Qv,double *ddtr);// transform ecef to geodetic postion ------------------------------------------// transform ecef position to geodetic position// args : double *r I ecef position {x,y,z} (m)// double *pos O geodetic position {lat,lon,h} (rad,m)// return : none// notes : WGS84, ellipsoidal height// -----------------------------------------------------------------------------*/extern void ecef2pos(const double *r, double *pos);/// transform ecef vector to local tangental coordinate ------------------------- // transform ecef vector to local tangental coordinate// args : double *pos I geodetic position {lat,lon} (rad)// double *r I vector in ecef coordinate {x,y,z}// double *e O vector in local tangental coordinate {e,n,u}// return : none// -----------------------------------------------------------------------------*/extern void ecef2enu(const double *pos, const double *r, double *e);RTKlib学习（二）：Glonass参数，该信哪一个？在了解Glonass卫星位置计算时，一般用四阶龙格－库塔算法，笔者在校时学的《数值计算方法》中有讲，不过也差不多忘完了，重新学习吧。
