/* sbas ionospheric delay correction -------------------------------------------
* compute sbas ionosphric delay correction
* args : gtime_t time I time
* nav_t *nav I navigation data
* double *pos I receiver position {lat,lon,height} (rad/m)
* double *azel I satellite azimuth/elavation angle (rad)
* double *delay O slant ionospheric delay (L1) (m)
* double *var O variance of ionospheric delay (m^2)
* return : status (1:ok, 0:no correction)
* notes : before calling the function, sbas ionosphere correction parameters
* in navigation data (nav->sbsion) must be set by callig
* sbsupdatecorr()
*-----------------------------------------------------------------------------*/
extern int sbsioncorr(gtime_t time, const nav_t *nav, const double *pos,
const double *azel, double *delay, double *var)
{
const double re=6378.1363,hion=350.0;
int i,err=0;
double fp,posp[2],x=0.0,y=0.0,t,w[4]={0};
const sbsigp_t *igp[4]={0}; /* {ws,wn,es,en} */
trace(4,"sbsioncorr: pos=%.3f %.3f azel=%.3f %.3f\n",pos[0]*R2D,pos[1]*R2D,
azel[0]*R2D,azel[1]*R2D);
*delay=*var=0.0;
if (pos[2]<-100.0||azel[1]<=0) return 1;
/* ipp (ionospheric pierce point) position */
fp=ionppp(pos,azel,re,hion,posp);
/* search igps around ipp */
searchigp(time,posp,nav->sbsion,igp,&x,&y);
/* weight of igps */
if (igp[0]&&igp[1]&&igp[2]&&igp[3]) {
w[0]=(1.0-x)*(1.0-y); w[1]=(1.0-x)*y; w[2]=x*(1.0-y); w[3]=x*y;
}
else if (igp[0]&&igp[1]&&igp[2]) {
w[1]=y; w[2]=x;
if ((w[0]=1.0-w[1]-w[2])<0.0) err=1;
}
else if (igp[0]&&igp[2]&&igp[3]) {
w[0]=1.0-x; w[3]=y;
if ((w[2]=1.0-w[0]-w[3])<0.0) err=1;
}
else if (igp[0]&&igp[1]&&igp[3]) {
w[0]=1.0-y; w[3]=x;
if ((w[1]=1.0-w[0]-w[3])<0.0) err=1;
}
else if (igp[1]&&igp[2]&&igp[3]) {
w[1]=1.0-x; w[2]=1.0-y;
if ((w[3]=1.0-w[1]-w[2])<0.0) err=1;
}
else err=1;
if (err) {
trace(2,"no sbas iono correction: lat=%3.0f lon=%4.0f\n",posp[0]*R2D,
posp[1]*R2D);
return 0;
}
for (i=0;i<4;i++) {
if (!igp[i]) continue;
t=timediff(time,igp[i]->t0);
*delay+=w[i]*igp[i]->delay;
*var+=w[i]*varicorr(igp[i]->give)*9E-8*fabs(t);
}
*delay*=fp; *var*=fp*fp;
trace(5,"sbsioncorr: dion=%7.2f sig=%7.2f\n",*delay,sqrt(*var));
return 1;
}
/* ionosphere delay by tec grid data -----------------------------------------*/
static int iondelay(gtime_t time, const tec_t *tec, const double *pos,
const double *azel, int opt, double *delay, double *var)
{
const double fact=40.30E16/FREQ1/FREQ1; /* tecu->L1 iono (m) */
double fs,posp[3]={0},vtec,rms,hion,rp;
int i;
trace(3,"iondelay: time=%s pos=%.1f %.1f azel=%.1f %.1f\n",time_str(time,0),
pos[0]*R2D,pos[1]*R2D,azel[0]*R2D,azel[1]*R2D);
*delay=*var=0.0;
for (i=0;i<tec->ndata[2];i++) { /* for a layer */
hion=tec->hgts[0]+tec->hgts[2]*i;
/* ionospheric pierce point position */
fs=ionppp(pos,azel,tec->rb,hion,posp);
if (opt&2) {
/* modified single layer mapping function (M-SLM) ref [2] */
rp=tec->rb/(tec->rb+hion)*sin(0.9782*(PI/2.0-azel[1]));
fs=1.0/sqrt(1.0-rp*rp);
}
if (opt&1) {
/* earth rotation correction (sun-fixed coordinate) */
posp[1]+=2.0*PI*timediff(time,tec->time)/86400.0;
}
/* interpolate tec grid data */
if (!interptec(tec,i,posp,&vtec,&rms)) return 0;
*delay+=fact*fs*vtec;
*var+=fact*fact*fs*fs*rms*rms;
}
trace(4,"iondelay: delay=%7.2f std=%6.2f\n",*delay,sqrt(*var));
return 1;
}
