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Library for calculating satellites positions and predicting overpasses.

License: MIT License

C 6.79% C++ 93.21%

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sgp4-library's Issues

Mathematical innacuracies

Seems like the result of invjday and findsat is off.
Compared to N2YO and gPredict, the nearest passes are off by 1-5 minutes, the current calculated direction of the satellite seems to be off, sometimes even by as much as 30 degrees elevation.

Is this a limitation of a simplified SGP4 or am I just being an idiot?

Disabled rates

Hi,
Thank you for this library. I'm planning to use it for my upcoming project related to the ISS.
I was wondering why did you comment all the code related to rates and velocity?
Have you had trouble to make it work on ESP? Or maybe it is due to performance considerations?
Do you think I can safely uncomment those lines to get the rates back?

Thank you

Compile error example SGP4Predictor

Receive “‘int min’ redeclared as a different type of symbol” error when compiling the SGP4 predictor example using either Arduino IDE or Web editor.

library crashes on ESP32

i,
Many thanks for this great library.
I did compile on ESP32 but crashes withthis error code at run : "stack smashing protect failure"

After investigation i found that the problem was into sgp4io.cpp when extracting float from the TLE for instance on this line:

memcpy( tempstr, &longstr1[20] , 12); tempstr[12] = '\0'; satrec.epochdays = atof(tempstr);

To solve the issue I have used String() arduino function.
satrec.epochdays = str1.substring(20, 32).toDouble();

include <arduino.h> into sgp4io.h
modify sgp4io.cpp with this version 👍 `/* ----------------------------------------------------------------

```
                          sgp4io.cpp
```
this file contains a function to read two line element sets. while
not formerly part of the sgp4 mathematical theory, it is
required for practical implemenation.

                       companion code for

          fundamentals of astrodynamics and applications

```
                               2007
```

                         by david vallado

  (w) 719-573-2600, email [email protected]

current :
```
         27 Aug 10  david vallado
```

                      fix input format and delete unused variables in twoline2rv

changes :
```
          3 sep 08  david vallado
```

                      add operationmode for afspc (a) or improved (i)

```
          9 may 07  david vallado
```

                      fix year correction to 57

```
         27 mar 07  david vallado
```

                      misc fixes to manual inputs

```
         14 aug 06  david vallado
```

                      original baseline

  ----------------------------------------------------------------      */

#include "sgp4io.h"
#include "stdlib.h"

/* -----------------------------------------------------------------------------
*

                      function twoline2rv

this function converts the two line element set character string data to
variables and initializes the sgp4 variables. several intermediate varaibles
and quantities are determined. note that the result is a structure so multiple
satellites can be processed simultaneously without having to reinitialize. the
verification mode is an important option that permits quick checks of any
changes to the underlying technical theory. this option works using a
modified tle file in which the start, stop, and delta time values are
included at the end of the second line of data. this only works with the
verification mode. the catalog mode simply propagates from -1440 to 1440 min
from epoch and is useful when performing entire catalog runs.
author : david vallado 719-573-2600 1 mar 2001
inputs :
longstr1 - first line of the tle
longstr2 - second line of the tle
typerun - type of run verification 'v', catalog 'c',

                                            manual 'm'

typeinput - type of manual input mfe 'm', epoch 'e', dayofyr 'd'
opsmode - mode of operation afspc or improved 'a', 'i'
whichconst - which set of constants to use 72, 84
outputs :
satrec - structure containing all the sgp4 satellite information
coupling :
getgravconst-
days2mdhms - conversion of days to month, day, hour, minute, second
jday - convert day month year hour minute second into julian date
sgp4init - initialize the sgp4 variables
references :
norad spacetrack report #3
vallado, crawford, hujsak, kelso 2006
--------------------------------------------------------------------------- */

void twoline2rv
(
char longstr1[130], char longstr2[130],
char opsmode, gravconsttype whichconst,
elsetrec& satrec
)
{
char tempstr[12];
const double deg2rad = pi / 180.0; // 0.0174532925199433
const double xpdotp = 1440.0 / (2.0 *pi); // 229.1831180523293

   double sec, mu, radiusearthkm, tumin, xke, j2, j3, j4, j3oj2;
   double startsec, stopsec, startdayofyr, stopdayofyr, jdstart, jdstop;
   int startyear, stopyear, startmon, stopmon, startday, stopday,
       starthr, stophr, startmin, stopmin;
   int cardnumb, numb, j;
   long revnum = 0, elnum = 0;
   char classification, intldesg[11];
   int year = 0;
   int mon, day, hr, minute, nexp, ibexp;

   getgravconst( whichconst, tumin, mu, radiusearthkm, xke, j2, j3, j4, j3oj2 );

   satrec.error = 0;

   // set the implied decimal points since doing a formated read
   // fixes for bad input data values (missing, ...)
   for (j = 10; j <= 15; j++)
       if (longstr1[j] == ' ')
           longstr1[j] = '_';

   if (longstr1[44] != ' ')
       longstr1[43] = longstr1[44];
   longstr1[44] = '.';
   if (longstr1[7] == ' ')
       longstr1[7] = 'U';
   if (longstr1[9] == ' ')
       longstr1[9] = '.';
   for (j = 45; j <= 49; j++)
       if (longstr1[j] == ' ')
           longstr1[j] = '0';
   if (longstr1[51] == ' ')
       longstr1[51] = '0';
   if (longstr1[53] != ' ')
       longstr1[52] = longstr1[53];
   longstr1[53] = '.';
   longstr2[25] = '.';
   for (j = 26; j <= 32; j++)
       if (longstr2[j] == ' ')
           longstr2[j] = '0';
   if (longstr1[62] == ' ')
       longstr1[62] = '0';
   if (longstr1[68] == ' ')
       longstr1[68] = '0';

   /**
   sscanf(longstr1,"%2d %5ld %1c %10s %2d %12lf %11lf %7lf %2d %7lf %2d %2d %6ld ",
                   &cardnumb,&satrec.satnum,&classification, intldesg, &satrec.epochyr,
                   &satrec.epochdays,&satrec.ndot, &satrec.nddot, &nexp, &satrec.bstar,
                   &ibexp, &numb, &elnum );
   **/
	String str1= String(longstr1);
   satrec.satnum = str1.substring(2, 7).toInt();
   	   satrec.epochyr = str1.substring(18, 20).toInt();
   satrec.epochdays = str1.substring(20, 32).toDouble();
	satrec.ndot = str1.substring(32, 43).toDouble();
	satrec.nddot = str1.substring(43, 50).toDouble();
	nexp = str1.substring(50, 52).toInt();
	satrec.bstar = str1.substring(52, 59).toDouble();
	ibexp = str1.substring(59, 61).toInt();
   //memcpy( tempstr, &longstr1[0] , 2); tempstr[1] = '\0'; satrec.cardnumb = atoi(tempstr); 
   //memcpy( tempstr, &longstr1[2] , 5); tempstr[5] = '\0'; satrec.satnum = atol(tempstr); //
   //classification = longstr1[7];
   //memcpy( intldesg, &longstr1[8] , 10); intldesg[10] = '\0';
   //memcpy( tempstr, &longstr1[18] , 2); tempstr[2] = '\0'; satrec.epochyr = atoi(tempstr); //
  // memcpy( tempstr, &longstr1[20] , 12); tempstr[12] = '\0'; satrec.epochdays = atof(tempstr);//
   //memcpy( tempstr, &longstr1[32] , 11); tempstr[11] = '\0'; satrec.ndot = atof(tempstr);
   //memcpy( tempstr, &longstr1[43] , 7); tempstr[7] = '\0'; satrec.nddot = atof(tempstr);//
   //memcpy( tempstr, &longstr1[50] , 2); tempstr[2] = '\0'; nexp = atoi(tempstr); //
   //memcpy( tempstr, &longstr1[52] , 7); tempstr[7] = '\0'; satrec.bstar = atof(tempstr);//
   //memcpy( tempstr, &longstr1[59] , 2); tempstr[2] = '\0'; ibexp = atoi(tempstr);//
   //memcpy( tempstr, &longstr1[61] , 2); tempstr[2] = '\0'; numb = atoi(tempstr);
   //memcpy( tempstr, &longstr1[63] , 6); tempstr[6] = '\0'; elnum = atol(tempstr);
	String str2= String(longstr2);
	satrec.satnum = str2.substring(2, 7).toInt();
	satrec.inclo = str2.substring(7, 16).toDouble();
	satrec.nodeo = str2.substring(16, 25).toDouble();
	satrec.ecco =  str2.substring(25, 33).toDouble();
	satrec.argpo = str2.substring(33, 42).toDouble();
	satrec.mo = str2.substring(42, 51).toDouble();
	satrec.no = str2.substring(51, 62).toDouble();
  // memcpy( tempstr, &longstr2[2] , 5); tempstr[5] = '\0'; satrec.satnum = atol(tempstr);//
   //memcpy( tempstr, &longstr2[7] , 9); tempstr[9] = '\0'; satrec.inclo = atof(tempstr);/
   //memcpy( tempstr, &longstr2[16] , 9); tempstr[9] = '\0'; satrec.nodeo = atof(tempstr);//
   //memcpy( tempstr, &longstr2[25] , 8); tempstr[8] = '\0'; satrec.ecco = atof(tempstr);//
   //memcpy( tempstr, &longstr2[33] , 9); tempstr[9] = '\0'; satrec.argpo = atof(tempstr);//
   //memcpy( tempstr, &longstr2[42] , 9); tempstr[9] = '\0'; satrec.mo = atof(tempstr);//
   //memcpy( tempstr, &longstr2[51] , 11); tempstr[10] = '\0'; satrec.no = atof(tempstr);//
   //memcpy( tempstr, &longstr2[63] , 6); tempstr[6] = '\0'; revnum = atol(tempstr);



   // ---- find no, ndot, nddot ----
   satrec.no   = satrec.no / xpdotp; //* rad/min
   satrec.nddot= satrec.nddot * pow(10.0, nexp);
   satrec.bstar= satrec.bstar * pow(10.0, ibexp);

   // ---- convert to sgp4 units ----
   satrec.a    = pow( satrec.no*tumin , (-2.0/3.0) );
   satrec.ndot = satrec.ndot  / (xpdotp*1440.0);  //* ? * minperday
   satrec.nddot= satrec.nddot / (xpdotp*1440.0*1440);

   // ---- find standard orbital elements ----
   satrec.inclo = satrec.inclo  * deg2rad;
   satrec.nodeo = satrec.nodeo  * deg2rad;
   satrec.argpo = satrec.argpo  * deg2rad;
   satrec.mo    = satrec.mo     * deg2rad;

   satrec.alta = satrec.a*(1.0 + satrec.ecco) - 1.0;
   satrec.altp = satrec.a*(1.0 - satrec.ecco) - 1.0;

   // ----------------------------------------------------------------
   // find sgp4epoch time of element set
   // remember that sgp4 uses units of days from 0 jan 1950 (sgp4epoch)
   // and minutes from the epoch (time)
   // ----------------------------------------------------------------

   // ---------------- temp fix for years from 1957-2056 -------------------
   // --------- correct fix will occur when year is 4-digit in tle ---------
   if (satrec.epochyr < 57)
       year= satrec.epochyr + 2000;
     else
       year= satrec.epochyr + 1900;

   days2mdhms ( year,satrec.epochdays, mon,day,hr,minute,sec );
   jday( year,mon,day,hr,minute,sec, 0,false,satrec.jdsatepoch );

   /***
   // ---- input start stop times manually
   if ((typerun != 'v') && (typerun != 'c'))
     {
     // ------------- enter start/stop ymd hms values --------------------
       if (typeinput == 'e')
         {
           printf("input start prop year mon day hr min sec \n");
           // make sure there is no space at the end of the format specifiers in scanf!
           scanf( "%i %i %i %i %i %lf",&startyear, &startmon, &startday, &starthr, &startmin, &startsec);
           fflush(stdin);
           jday( startyear,startmon,startday,starthr,startmin,startsec, jdstart );

           printf("input stop prop year mon day hr min sec \n");
           scanf( "%i %i %i %i %i %lf",&stopyear, &stopmon, &stopday, &stophr, &stopmin, &stopsec);
           fflush(stdin);
           jday( stopyear,stopmon,stopday,stophr,stopmin,stopsec, jdstop );

           startmfe = (jdstart - satrec.jdsatepoch) * 1440.0;
           stopmfe  = (jdstop - satrec.jdsatepoch) * 1440.0;

           printf("input time step in minutes \n");
           scanf( "%lf",&deltamin );
         }
       // -------- enter start/stop year and days of year values -----------
       if (typeinput == 'd')
         {
           printf("input start year dayofyr \n");
           scanf( "%i %lf",&startyear, &startdayofyr );
           printf("input stop year dayofyr \n");
           scanf( "%i %lf",&stopyear, &stopdayofyr );

           days2mdhms ( startyear,startdayofyr, mon,day,hr,minute,sec );
           jday( startyear,mon,day,hr,minute,sec, jdstart );
           days2mdhms ( stopyear,stopdayofyr, mon,day,hr,minute,sec );
           jday( stopyear,mon,day,hr,minute,sec, jdstop );

           startmfe = (jdstart - satrec.jdsatepoch) * 1440.0;
           stopmfe  = (jdstop - satrec.jdsatepoch) * 1440.0;

           printf("input time step in minutes \n");
           scanf( "%lf",&deltamin );
         }
       // ------------------ enter start/stop mfe values -------------------
       if (typeinput == 'm')
         {
           printf("input start min from epoch \n");
           scanf( "%lf",&startmfe );
           printf("input stop min from epoch \n");
           scanf( "%lf",&stopmfe );
           printf("input time step in minutes \n");
           scanf( "%lf",&deltamin );
         }
     }
   ***/
   // ---------------- initialize the orbit at sgp4epoch -------------------
   sgp4init( whichconst, opsmode, satrec.satnum, satrec.jdsatepoch-2433281.5, satrec.bstar,
             satrec.ecco, satrec.argpo, satrec.inclo, satrec.mo, satrec.no,
             satrec.nodeo, satrec);
} // end twoline2rv

/* -----------------------------------------------------------------------------
*

                      function twolineChecksum

this function checks if the checksum on the end of the line is correct.
author : Hopperpop 6 mar 2016
inputs :
longstr - line of the tle
outputs :
bool - true if test was succesfull
references :
https://en.wikipedia.org/wiki/Two-line_element_set
--------------------------------------------------------------------------- */
bool twolineChecksum
(
const char longstr[80]
)
{

unsigned int cks = 0;
const char* checksumpointer = longstr + 68;

for (const char* p = longstr; p < checksumpointer; p++){

    switch(*p){
        case 0:
          return false;
          break;
        case '-':
          cks++;
          break;
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
          cks += *p - '0';
          break;
    }

}
cks %= 10;   //modulo 10
if (cks + '0' == *checksumpointer)
  return true;

return false;

}
`

This mod now works with ESP32 arduino and should work as well with ESP8266

Once again thank you for this lib
JP

Please add this library to the Arduino Library Manager

Hello @Hopperpop ,

Thank you again for sharing this library. It is a really nice piece of work!

Could you please add this library to the Arduino Library Manager - so it can be installed automatically through the Arduino IDE?

You can find full instructions on how to add a library to the registry here:
https://github.com/arduino/library-registry

(Please do include PR #5 and up-issue the library tag first. Thank you!)

Sincere thanks,
Paul

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