Diff: sgp4sdp4/sgp_in.c

Revision:

0:0a841b89d614

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sgp4sdp4/sgp_in.c	Mon Oct 11 10:34:55 2010 +0000
@@ -0,0 +1,251 @@
+/* Unit SGP_In */
+/*           Author:  Dr TS Kelso */
+/* Original Version:  1992 Jun 25 */
+/* Current Revision:  1999 Nov 27 */
+/*          Version:  2.10 */
+/*        Copyright:  1992-1999, All Rights Reserved */
+
+/* Ported to C by N. Kyriazis  April 6  2001 */
+
+#include "sgp4sdp4.h"
+
+/* Calculates the checksum mod 10 of a line from a TLE set and */
+/* returns 1 if it compares with checksum in column 68, else 0.*/
+/* tle_set is a character string holding the two lines read    */
+/* from a text file containing NASA format Keplerian elements. */
+int
+Checksum_Good( char *tle_set )
+{
+  int i, check_digit, value, checksum = 0;
+
+  for(i = 0; i < 68; i++)
+    {
+      if( (tle_set[i] >= '0') && (tle_set[i] <= '9') )
+    value = tle_set[i] - '0';
+      else if( tle_set[i] == '-' )
+    value = 1;
+      else
+    value = 0;
+
+      checksum += value;
+    } /* End for(i = 0; i < 68; i++) */
+
+  checksum %= 10;
+  check_digit = tle_set[68] - '0';
+
+  return( checksum == check_digit );
+} /* Function Checksums_Good */
+
+/*------------------------------------------------------------------*/
+
+/* Carries out various checks on a TLE set to verify its validity */
+/* tle_set is a character string holding the two lines read    */
+/* from a text file containing NASA format Keplerian elements. */
+int
+Good_Elements( char *tle_set )
+{
+  /* Verify checksum of both lines of a TLE set */
+  if( !Checksum_Good(&tle_set[0]) || !Checksum_Good(&tle_set[69]) )
+    return (0);
+  /* Check the line number of each line */
+  if( (tle_set[0] != '1') || (tle_set[69] != '2') )
+    return (0);
+  /* Verify that Satellite Number is same in both lines */
+  if( strncmp( &tle_set[2], &tle_set[71], 5 ) != 0 )
+    return (0);
+  /* Check that various elements are in the right place */
+  if( 
+     (tle_set[ 23] != '.') ||
+     (tle_set[ 34] != '.') ||
+     (tle_set[ 80] != '.') ||
+     (tle_set[ 89] != '.') ||
+     (tle_set[106] != '.') ||
+     (tle_set[115] != '.') ||
+     (tle_set[123] != '.') ||
+     (strncmp(&tle_set[61], " 0 ", 3) != 0)
+     )
+    return (0);
+
+  return(1);
+}  /* Function Good_Elements */
+
+/*------------------------------------------------------------------*/
+
+/* Converts the strings in a raw two-line element set  */
+/* to their intended numerical values. No processing   */
+/* of these values is done, e.g. from deg to rads etc. */
+/* This is done in the select_ephemeris() function.    */
+void
+Convert_Satellite_Data( char *tle_set, tle_t *tle )
+{ 
+  char buff[15];
+
+  /** Decode Card 1 **/
+  /* Satellite's catalogue number */
+  strncpy( buff, &tle_set[2],5 );
+  buff[5] = '\0';
+  tle->catnr = atoi(buff);
+
+  /* International Designator for satellite */
+  strncpy( tle->idesg, &tle_set[9],8 );
+  tle->idesg[8] = '\0';
+
+  /* Satellite's epoch */
+  strncpy( buff, &tle_set[18],14 );
+  buff[14] = '\0';
+  tle->epoch = atof(buff);
+
+  /* Satellite's First Time Derivative */
+  strncpy( buff, &tle_set[33],10 );
+  buff[10]='\0';
+  tle->xndt2o = atof(buff);
+
+  /* Satellite's Second Time Derivative */
+  strncpy( buff, &tle_set[44],1 );
+  buff[1] = '.';
+  strncpy( &buff[2], &tle_set[45],5 );
+  buff[7] = 'E';
+  strncpy( &buff[8], &tle_set[50],2 );
+  buff[10]='\0';
+  tle->xndd6o = atof(buff);
+
+  /* Satellite's bstar drag term */
+  strncpy( buff, &tle_set[53],1 );
+  buff[1] = '.';
+  strncpy( &buff[2], &tle_set[54],5 );
+  buff[7] = 'E';
+  strncpy( &buff[8], &tle_set[59],2 );
+  buff[10]='\0';
+  tle->bstar = atof(buff);
+
+  /* Element Number */
+  strncpy( buff, &tle_set[64],4 );
+  buff[4]='\0';
+  tle->elset = atoi(buff);
+
+  /** Decode Card 2 **/
+  /* Satellite's Orbital Inclination (degrees) */
+  strncpy( buff, &tle_set[77], 8 );
+  buff[8]='\0';
+  tle->xincl = atof(buff);
+
+  /* Satellite's RAAN (degrees) */
+  strncpy( buff, &tle_set[86], 8 );
+  buff[8]='\0';
+  tle->xnodeo = atof(buff);
+
+  /* Satellite's Orbital Eccentricity */
+  buff[0] = '.';
+  strncpy( &buff[1], &tle_set[95], 7 );
+  buff[8]='\0';
+  tle->eo = atof(buff);
+
+  /* Satellite's Argument of Perigee (degrees) */
+  strncpy( buff, &tle_set[103], 8 );
+  buff[8]='\0';
+  tle->omegao = atof(buff);
+
+  /* Satellite's Mean Anomaly of Orbit (degrees) */
+  strncpy( buff, &tle_set[112], 8 );
+  buff[8]='\0';
+  tle->xmo = atof(buff);
+
+  /* Satellite's Mean Motion (rev/day) */
+  strncpy( buff, &tle_set[121], 10 );
+  buff[10]='\0';
+  tle->xno = atof(buff);
+
+  /* Satellite's Revolution number at epoch */
+  strncpy( buff, &tle_set[132], 5 );
+  buff[5]='\0';
+  tle->revnum = atof(buff);
+
+} /* Procedure Convert_Satellite_Data */
+
+/*------------------------------------------------------------------*/
+
+int
+Get_Next_Tle_Set( char line[3][80], tle_t *tle)
+{
+  int idx,  /* Index for loops and arrays    */
+      chr;  /* Used for inputting characters */
+
+  char tle_set[139]; /* Two lines of a TLE set */
+
+  /* Read the satellite's name */
+  for (idx = 0 ; idx < 25; idx++)
+  {
+      if( ((chr = line[0][idx]) != CR) && (chr != LF) && (chr != '\0'))
+      tle->sat_name[idx] = chr;
+      else
+      {
+      /* strip off trailing spaces */
+      while ((chr = line[0][--idx]) == ' ');
+      tle->sat_name[++idx] = '\0';
+        break;
+      }
+  }
+
+  /* Read in first line of TLE set */
+  strncpy(tle_set, line[1], 70);
+  
+  /* Read in second line of TLE set and terminate string */
+  strncpy(&tle_set[69], line[2], 70);
+  tle_set[138]='\0';
+  
+  /* Check TLE set and abort if not valid */
+  if( !Good_Elements(tle_set) )
+    return(-2);
+
+  /* Convert the TLE set to orbital elements */
+  Convert_Satellite_Data( tle_set, tle );
+
+  return(1);
+}
+
+/*------------------------------------------------------------------*/
+
+/* Selects the apropriate ephemeris type to be used */
+/* for predictions according to the data in the TLE */
+/* It also processes values in the tle set so that  */
+/* they are apropriate for the sgp4/sdp4 routines   */
+void
+select_ephemeris(tle_t *tle)
+{
+  double ao,xnodp,dd1,dd2,delo,temp,a1,del1,r1;
+
+  /* Preprocess tle set */
+  tle->xnodeo *= de2ra;
+  tle-> omegao *= de2ra;
+  tle->xmo *= de2ra;
+  tle->xincl *= de2ra;
+  temp = twopi/xmnpda/xmnpda;
+  tle->xno = tle->xno*temp*xmnpda;
+  tle->xndt2o *= temp;
+  tle->xndd6o = tle->xndd6o*temp/xmnpda;
+  tle->bstar /= ae;
+
+  /* Period > 225 minutes is deep space */
+  dd1 = (xke/tle->xno);
+  dd2 = tothrd;
+  a1 = pow(dd1, dd2);
+  r1 = cos(tle->xincl);
+  dd1 = (1.0-tle->eo*tle->eo);
+  temp = ck2*1.5f*(r1*r1*3.0-1.0)/pow(dd1, 1.5);
+  del1 = temp/(a1*a1);
+  ao = a1*(1.0-del1*(tothrd*.5+del1*
+             (del1*1.654320987654321+1.0)));
+  delo = temp/(ao*ao);
+  xnodp = tle->xno/(delo+1.0);
+
+  /* Select a deep-space/near-earth ephemeris */
+  if (twopi/xnodp/xmnpda >= .15625)
+    SetFlag(DEEP_SPACE_EPHEM_FLAG);
+  else
+    ClearFlag(DEEP_SPACE_EPHEM_FLAG);
+
+  return;
+} /* End of select_ephemeris() */
+
+/*------------------------------------------------------------------*/
+