250 lines
4.9 KiB
C
250 lines
4.9 KiB
C
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#include <stdio.h>
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#include <string.h>
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#include <math.h>
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#include "sgdp4h.h"
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#include "satutl.h"
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#define LIM 80
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#define D2R M_PI/180.0
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#define R2D 180.0/M_PI
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#define XKMPER 6378.135 // Earth radius in km
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#define XKMPAU 149597879.691 // AU in km
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#define FLAT (1.0/298.257)
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#define C 299792.458 // Speed of light in km/s
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struct point {
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xyz_t obspos,obsvel;
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};
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struct site {
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int id;
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double lng,lat;
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float alt;
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char observer[64];
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};
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struct trace {
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int satno,n;
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double *mjd;
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double *freq;
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float *za;
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};
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// Return x modulo y [0,y)
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double modulo(double x,double y)
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{
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x=fmod(x,y);
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if (x<0.0) x+=y;
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return x;
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}
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// Read a line of maximum length int lim from file FILE into string s
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int fgetline(FILE *file,char *s,int lim)
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{
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int c,i=0;
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while (--lim > 0 && (c=fgetc(file)) != EOF && c != '\n')
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s[i++] = c;
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// if (c == '\n')
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// s[i++] = c;
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s[i] = '\0';
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return i;
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}
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// Greenwich Mean Sidereal Time
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double gmst(double mjd)
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{
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double t,gmst;
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t=(mjd-51544.5)/36525.0;
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gmst=modulo(280.46061837+360.98564736629*(mjd-51544.5)+t*t*(0.000387933-t/38710000),360.0);
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return gmst;
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}
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// Greenwich Mean Sidereal Time
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double dgmst(double mjd)
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{
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double t,dgmst;
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t=(mjd-51544.5)/36525.0;
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dgmst=360.98564736629+t*(0.000387933-t/38710000);
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return dgmst;
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}
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// Observer position
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void obspos_xyz(double mjd,double lng,double lat,float alt,xyz_t *pos,xyz_t *vel)
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{
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double ff,gc,gs,theta,s,dtheta;
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s=sin(lat*D2R);
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ff=sqrt(1.0-FLAT*(2.0-FLAT)*s*s);
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gc=1.0/ff+alt/XKMPER;
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gs=(1.0-FLAT)*(1.0-FLAT)/ff+alt/XKMPER;
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theta=gmst(mjd)+lng;
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dtheta=dgmst(mjd)*D2R/86400;
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pos->x=gc*cos(lat*D2R)*cos(theta*D2R)*XKMPER;
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pos->y=gc*cos(lat*D2R)*sin(theta*D2R)*XKMPER;
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pos->z=gs*sin(lat*D2R)*XKMPER;
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vel->x=-gc*cos(lat*D2R)*sin(theta*D2R)*XKMPER*dtheta;
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vel->y=gc*cos(lat*D2R)*cos(theta*D2R)*XKMPER*dtheta;
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vel->z=0.0;
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return;
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}
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// Get observing site
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struct site get_site(int site_id)
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{
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int i=0;
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char line[LIM];
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FILE *file;
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int id;
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double lat,lng;
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float alt;
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char abbrev[3],observer[64];
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struct site s;
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char *env,filename[LIM];
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env=getenv("ST_DATADIR");
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sprintf(filename,"%s/data/sites.txt",env);
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file=fopen(filename,"r");
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if (file==NULL) {
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printf("File with site information not found!\n");
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return;
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}
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while (fgets(line,LIM,file)!=NULL) {
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// Skip
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if (strstr(line,"#")!=NULL)
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continue;
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// Strip newline
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line[strlen(line)-1]='\0';
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// Read data
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sscanf(line,"%4d %2s %lf %lf %f",
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&id,abbrev,&lat,&lng,&alt);
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strcpy(observer,line+38);
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// Change to km
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alt/=1000.0;
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// Copy site
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if (id==site_id) {
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s.lat=lat;
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s.lng=lng;
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s.alt=alt;
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s.id=id;
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strcpy(s.observer,observer);
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}
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}
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fclose(file);
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return s;
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}
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// Compute trace
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struct trace *compute_trace(double *mjd,int n,int site_id,float fmin,float fmax,int *nsat)
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{
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int i,j,imode,flag,satno,tflag;
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struct point *p;
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struct site s;
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FILE *file,*infile;
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orbit_t orb;
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xyz_t satpos,satvel;
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double dx,dy,dz,dvx,dvy,dvz,r,v,za;
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double freq,freq0;
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char line[LIM],text[8];
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struct trace *t;
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// Find number of satellites in frequency range
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infile=fopen("frequencies.txt","r");
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for (i=0;;) {
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if (fgetline(infile,line,LIM)<=0)
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break;
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sscanf(line,"%d %lf",&satno,&freq0);
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if (freq0>=fmin && freq0<=fmax)
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i++;
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}
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fclose(infile);
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*nsat=i;
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// Allocate traces
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t=(struct trace *) malloc(sizeof(struct trace)* *nsat);
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// Get site
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s=get_site(site_id);
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// Allocate
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p=(struct point *) malloc(sizeof(struct point)*n);
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// Get observer position
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for (i=0;i<n;i++)
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obspos_xyz(mjd[i],s.lng,s.lat,s.alt,&p[i].obspos,&p[i].obsvel);
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infile=fopen("frequencies.txt","r");
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for (j=0;;) {
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if (fgetline(infile,line,LIM)<=0)
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break;
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sscanf(line,"%d %lf",&satno,&freq0);
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if (freq0<fmin || freq0>fmax)
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continue;
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// Allocate
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t[j].satno=satno;
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t[j].n=n;
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t[j].mjd=(double *) malloc(sizeof(double)*n);
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t[j].freq=(double *) malloc(sizeof(double)*n);
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t[j].za=(float *) malloc(sizeof(float)*n);
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sprintf(text," %d",satno);
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// Loop over TLEs
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file=fopen("/home/bassa/code/c/satellite/sattools/tle/bulk.tle","r");
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while (read_twoline(file,satno,&orb)==0) {
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// Initialize
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imode=init_sgdp4(&orb);
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if (imode==SGDP4_ERROR)
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printf("Error\n");
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// Loop over points
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for (i=0,flag=0,tflag=0;i<n;i++) {
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// Get satellite position
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satpos_xyz(mjd[i]+2400000.5,&satpos,&satvel);
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dx=satpos.x-p[i].obspos.x;
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dy=satpos.y-p[i].obspos.y;
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dz=satpos.z-p[i].obspos.z;
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dvx=satvel.x-p[i].obsvel.x;
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dvy=satvel.y-p[i].obsvel.y;
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dvz=satvel.z-p[i].obsvel.z;
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r=sqrt(dx*dx+dy*dy+dz*dz);
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v=(dvx*dx+dvy*dy+dvz*dz)/r;
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za=acos((p[i].obspos.x*dx+p[i].obspos.y*dy+p[i].obspos.z*dz)/(r*XKMPER))*R2D;
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freq=(1.0-v/C)*freq0;
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// Store
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t[j].mjd[i]=mjd[i];
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t[j].freq[i]=freq;
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t[j].za[i]=za;
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}
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}
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fclose(file);
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j++;
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}
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fclose(infile);
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// Free
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free(p);
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return t;
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}
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