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chestr.c

/* Copyright: 1Earth Research, LLC
 * All Rights Reserved
 * December 11, 2004
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>

/*----------------------------------------------------------------------------*/
/* function prototypes */
long checksum (char *s, long nch, int ifl);

/*******************************************************************************
* PROGRAM NAME: chestr
*   Converts a TLE satellite number to a new user-entererd number, 
*       making sure that the checksum is also changed.
* Inputs:
*   Name of the TLE file
* Outputs:
*   Modified TLE file with different name
* Return value:
*   0 on successful completion
* Includes required:
*   (none)
* Non-ANSI functions/macros/globals referenced:
*   (none)
* Comments/Reference:
*   (none)
* Modification History:
*   041211  R.G. Gist       First release
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
int main (int argc, char **argv)

#define MAXCHR 512 /* max # of characters in a line */
{
    FILE *fp1,*fp2;
    char *line,*file_name,*new_file_name;
        char curr_num[6],new_num[6],s[MAXCHR],input[5];
    int i,j,l,lnum=0;
        int modified_line_1_flag=0;
        long chksm;
    long il,jl;

    line=(char *) malloc (MAXCHR*sizeof(char));
    file_name=(char *) malloc (MAXCHR*sizeof(char));
    new_file_name=(char *) malloc (MAXCHR*sizeof(char));

        printf("\n\n        ---------------------      \n");
        printf("        TLE CHECKSUM MODIFIER   \n");
        printf("        ---------------------      \n");
        printf("        1Earth Research, LLC       \n");
        printf("        [email protected]    \n\n");

        if (argc==1) {
          printf("This program scans a file for two-line element sets (TLES)\n");
          printf("When a TLE is detected, the object number is reported to\n");
          printf("the user. The user can keep the number, or enter a new one.\n");
          printf("If a new number is entered, a new checksum will be computed\n");
          printf("for that object.\n");
          printf("\n");
        }

    /* console input */
    if (argc!=2 || argv[1]=="?") {
          fprintf(stderr,"Usage: chestr filename");
          return(1);
        }
    
        strncpy(file_name,argv[1],MAXCHR);
        /* printf("TLE filename: %s\n",file_name); */

        sprintf(new_file_name,"new_%s",file_name);
        /* printf("new TLE filename: %s\n",new_file_name); */

    if (!(fp1=fopen(file_name,"r"))) {
          fprintf(stderr,"Can\'t open input file \'%s\'.",file_name);
          return(1);
        }
    if (!(fp2=fopen(new_file_name,"w"))) {
      fprintf(fp2,new_file_name,"Can\'t open output file \'%s\'.",
            new_file_name);
          return(1);
    }

    /* Read in lines until end of file */
    while (!feof(fp1)) {

          lnum++;

          /* If end of file, kick out of loop */
          if ( fgets(line,MAXCHR,fp1) == NULL ) break;

          l=strlen(line);

          /* Test for a TLE first line */
          if (line[0]=='1' && line[1]==' ') {

            /* Check length of line */
            if (l!=71) {
              printf("Apparent TLE line 1 (line %d of %s) ",lnum,file_name);
              printf("does not have the right number of characters.\n");
              printf("It should be of the format:\n");
              printf("1 88888U          04313.81696759  .00000000  ");
              printf("00000-0  00000-0 0    38\n");
              return(1);
            }

            /* Report first line of TLE */
            printf("TLE found...\n");

            /* Read current object number from first line */
            for (i=0; i<5; i++) {
              curr_num[i]=line[i+2];
            }
            curr_num[i]='\0';
            printf("\tCurrent object number: %s\n",curr_num);

            /* Prompt user for new number */
            printf("\tEnter new object number [Enter to skip]: ");
            fgets(s,MAXCHR,stdin);
            /* fscanf(stdin,"%s",&s); */ /* Doesn't allow skip */
            l=strlen(s);
            if (l==1) {
              printf("\tCurrent number kept.\n");

            } else {

              /* Clean up and format the input string */
              strcpy(new_num,"00000");
              for (i=0,j=0; i<l; i++) {
                if (s[i]>47 && s[i]<58) input[j++]=s[i];
              }
              input[j]='\0';
              l=strlen(input);
              for (i=l; i>=0; i--) {
                new_num[i+5-l]=input[i];
              }
              printf("\tNew number: %s\n",new_num);

              /* Insert new number in place of the old one */
              for (i=4; i>=0; i--) {
                line[i+2]=new_num[i];
              }

              /* Compute new checksum */
              chksm=checksum(line,68,1);
              printf("\tchecksum: %ld\n",chksm%10);

              /* Insert new checksum into line */
              sprintf(line+68,"%ld\r\n",chksm%10);

              /* Insert new checksum into line */

              modified_line_1_flag=1;
            }

            /* Write (possibly) modified line to new file */
            fprintf(fp2,"%s",line);

          } else if (line[0]=='2' && line[1]==' ') {

            /* Check length of line */
            if (l!=71) {
              printf("Apparent TLE line 2 (line %d of %s) ",lnum,file_name);
              printf("does not have the right number of characters.\n");
              printf("It should be of the format:\n");
              printf("2 88888  28.8016 156.5475 0061387 291.2918 ");
              printf("216.6065 16.21858240    00\n");
              return(1);
            }

            /* Report second line of TLE */
            /* printf("second line of TLE\n"); */

            if (modified_line_1_flag==1) {
              /* Insert new number in place of the old one */
              for (i=4; i>=0; i--) {
                line[i+2]=new_num[i];
              }

              /* Compute new checksum */
              chksm=checksum(line,68,1);
              printf("\tchecksum: %ld\n",chksm%10);

              /* Insert new checksum into line */
              sprintf(line+68,"%ld\r\n",chksm%10);

              modified_line_1_flag=0;
            }

            /* Write (possibly) modified line to new file */
            fprintf(fp2,"%s",line);

            /* Not a TLE line.  Echo to new file */
          } else {
            fprintf(fp2,"%s",line);
          }
    }

        printf("\nModified TLEs written to: %s\n",new_file_name);

    free(line);

    fclose(fp1);
    fclose(fp2);


    return(0);
}
 
long checksum (char *s, long nch, int ifl)
{
    long i,into_num=0,sum=0;

    for (i=0;i<nch;i++,s++) {
        if (*s=='\n') break;
        if (*s==' ') {
            if (ifl || !into_num) continue;
            break;
        } else if (*s=='-') {
            into_num=1;
            sum++;
        } else if (*s=='+' || *s=='&') {
            into_num=1;
        } else if (*s>='0' && *s<='9') { /* found a number */
            into_num=1;
            sum+=(*s-'0');
        }
    }
    return (sum);
}
/******************************************************************************/

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