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/* Author: Dr TS Kelso */
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/* Original Version: 1992 Jun 25 */
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/* Current Revision: 1999 Nov 27 */
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/* Copyright: 1992-1999, All Rights Reserved */
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/* Ported to C by N. Kyriazis April 6 2001 */
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/* Calculates the checksum mod 10 of a line from a TLE set and */
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/* returns 1 if it compares with checksum in column 68, else 0.*/
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/* tle_set is a character string holding the two lines read */
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/* from a text file containing NASA format Keplerian elements. */
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Checksum_Good( char *tle_set )
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int i, check_digit, value, checksum = 0;
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for(i = 0; i < 68; i++)
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if( (tle_set[i] >= '0') && (tle_set[i] <= '9') )
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value = tle_set[i] - '0';
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else if( tle_set[i] == '-' )
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} /* End for(i = 0; i < 68; i++) */
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check_digit = tle_set[68] - '0';
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return( checksum == check_digit );
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} /* Function Checksums_Good */
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/*------------------------------------------------------------------*/
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/* Carries out various checks on a TLE set to verify its validity */
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/* tle_set is a character string holding the two lines read */
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/* from a text file containing NASA format Keplerian elements. */
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Good_Elements( char *tle_set )
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/* Verify checksum of both lines of a TLE set */
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if( !Checksum_Good(&tle_set[0]) || !Checksum_Good(&tle_set[69]) )
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/* Check the line number of each line */
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if( (tle_set[0] != '1') || (tle_set[69] != '2') )
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/* Verify that Satellite Number is same in both lines */
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if( strncmp( &tle_set[2], &tle_set[71], 5 ) != 0 )
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/* Check that various elements are in the right place */
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(tle_set[ 23] != '.') ||
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(tle_set[ 34] != '.') ||
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(tle_set[ 80] != '.') ||
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(tle_set[ 89] != '.') ||
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(tle_set[106] != '.') ||
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(tle_set[115] != '.') ||
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(tle_set[123] != '.') ||
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(strncmp(&tle_set[61], " 0 ", 3) != 0)
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} /* Function Good_Elements */
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/*------------------------------------------------------------------*/
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/* Converts the strings in a raw two-line element set */
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/* to their intended numerical values. No processing */
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/* of these values is done, e.g. from deg to rads etc. */
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/* This is done in the select_ephemeris() function. */
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Convert_Satellite_Data( char *tle_set, tle_t *tle )
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/* Satellite's catalogue number */
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strncpy( buff, &tle_set[2],5 );
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tle->catnr = atoi(buff);
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/* International Designator for satellite */
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strncpy( tle->idesg, &tle_set[9],8 );
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/* Satellite's epoch */
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strncpy( buff, &tle_set[18],14 );
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tle->epoch = atof(buff);
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/* Satellite's First Time Derivative */
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strncpy( buff, &tle_set[33],10 );
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tle->xndt2o = atof(buff);
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/* Satellite's Second Time Derivative */
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strncpy( buff, &tle_set[44],1 );
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strncpy( &buff[2], &tle_set[45],5 );
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strncpy( &buff[8], &tle_set[50],2 );
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tle->xndd6o = atof(buff);
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/* Satellite's bstar drag term */
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strncpy( buff, &tle_set[53],1 );
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strncpy( &buff[2], &tle_set[54],5 );
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strncpy( &buff[8], &tle_set[59],2 );
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tle->bstar = atof(buff);
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strncpy( buff, &tle_set[64],4 );
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tle->elset = atoi(buff);
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/** Decode Card 2 **/
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/* Satellite's Orbital Inclination (degrees) */
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strncpy( buff, &tle_set[77], 8 );
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tle->xincl = atof(buff);
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/* Satellite's RAAN (degrees) */
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strncpy( buff, &tle_set[86], 8 );
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tle->xnodeo = atof(buff);
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/* Satellite's Orbital Eccentricity */
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strncpy( &buff[1], &tle_set[95], 7 );
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tle->eo = atof(buff);
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/* Satellite's Argument of Perigee (degrees) */
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strncpy( buff, &tle_set[103], 8 );
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tle->omegao = atof(buff);
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/* Satellite's Mean Anomaly of Orbit (degrees) */
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strncpy( buff, &tle_set[112], 8 );
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tle->xmo = atof(buff);
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/* Satellite's Mean Motion (rev/day) */
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strncpy( buff, &tle_set[121], 10 );
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tle->xno = atof(buff);
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/* Satellite's Revolution number at epoch */
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strncpy( buff, &tle_set[132], 5 );
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tle->revnum = atof(buff);
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} /* Procedure Convert_Satellite_Data */
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/*------------------------------------------------------------------*/
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Get_Next_Tle_Set( char line[3][80], tle_t *tle)
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int idx, /* Index for loops and arrays */
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chr; /* Used for inputting characters */
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char tle_set[139]; /* Two lines of a TLE set */
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/* Read the satellite's name */
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for (idx = 0 ; idx < 25; idx++)
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if( ((chr = line[0][idx]) != CR) && (chr != LF) && (chr != '\0'))
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tle->sat_name[idx] = chr;
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/* strip off trailing spaces */
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while ((chr = line[0][--idx]) == ' ');
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tle->sat_name[++idx] = '\0';
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/* Read in first line of TLE set */
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strncpy(tle_set, line[1], 70);
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/* Read in second line of TLE set and terminate string */
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strncpy(&tle_set[69], line[2], 70);
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/* Check TLE set and abort if not valid */
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if( !Good_Elements(tle_set) )
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/* Convert the TLE set to orbital elements */
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Convert_Satellite_Data( tle_set, tle );
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/*------------------------------------------------------------------*/
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/* Selects the apropriate ephemeris type to be used */
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/* for predictions according to the data in the TLE */
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/* It also processes values in the tle set so that */
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/* they are apropriate for the sgp4/sdp4 routines */
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select_ephemeris(tle_t *tle)
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double ao,xnodp,dd1,dd2,delo,temp,a1,del1,r1;
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/* Preprocess tle set */
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tle->xnodeo *= de2ra;
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tle-> omegao *= de2ra;
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temp = twopi/xmnpda/xmnpda;
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tle->xno = tle->xno*temp*xmnpda;
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tle->xndd6o = tle->xndd6o*temp/xmnpda;
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/* Period > 225 minutes is deep space */
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dd1 = (xke/tle->xno);
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r1 = cos(tle->xincl);
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dd1 = (1.0-tle->eo*tle->eo);
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temp = ck2*1.5f*(r1*r1*3.0-1.0)/pow(dd1, 1.5);
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ao = a1*(1.0-del1*(tothrd*.5+del1*
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(del1*1.654320987654321+1.0)));
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xnodp = tle->xno/(delo+1.0);
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/* Select a deep-space/near-earth ephemeris */
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if (twopi/xnodp/xmnpda >= .15625)
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SetFlag(DEEP_SPACE_EPHEM_FLAG);
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ClearFlag(DEEP_SPACE_EPHEM_FLAG);
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} /* End of select_ephemeris() */
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/*------------------------------------------------------------------*/
added
removed
libsgp4sdp4/sgp_in.c
