twoline2satrec function

Map<String, dynamic> twoline2satrec(String longstr1, String longstr2)

Return a Satellite imported from two lines of TLE data.

Provide the two TLE lines as strings 'longstr1' and 'longstr2', and select which standard set of gravitational finalants you want by providing 'gravity_finalants':

'sgp4.propagation.wgs72' - Standard WGS 72 model 'sgp4.propagation.wgs84' - More recent WGS 84 model 'sgp4.propagation.wgs72old' - Legacy support for old SGP4 behavior

Normally, computations are made using various recent improvements to the algorithm. If you want to turn some of these off and go back into "afspc" mode, then set 'afspc_mode' to 'True'.

Implementation

Map<String, dynamic> twoline2satrec(String longstr1, String longstr2) {
  final opsmode = 'i';
  final xpdotp = 1440.0 / (2.0 * pi); // 229.1831180523293;
  var year = 0;

  final Map<String, dynamic> satrec = {};
  satrec['error'] = 0;

  satrec['satnum'] = longstr1.substring(2, 7);

  satrec['epochyr'] = int.parse(longstr1.substring(18, 20));
  satrec['epochdays'] = double.parse(longstr1.substring(20, 32));
  satrec['ndot'] = double.parse(longstr1.substring(33, 43));
  satrec['nddot'] = double.parse(
    '.${int.parse(longstr1.substring(44, 50))}E${longstr1.substring(50, 52)}',
  );
  satrec['bstar'] = double.parse(
    '${longstr1.substring(53, 54)}.${int.parse(longstr1.substring(54, 59))}E${longstr1.substring(59, 61)}',
  );

  // satrec['satnum'] = longstr2.substring(2, 7);
  satrec['inclo'] = double.parse(longstr2.substring(8, 16));
  satrec['nodeo'] = double.parse(longstr2.substring(17, 25));
  satrec['ecco'] = double.parse('.${longstr2.substring(26, 33)}');
  satrec['argpo'] = double.parse(longstr2.substring(34, 42));
  satrec['mo'] = double.parse(longstr2.substring(43, 51));
  satrec['no'] = double.parse(longstr2.substring(52, 63));

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

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

  // ---- find standard orbital elements ----
  satrec['inclo'] *= deg2rad;
  satrec['nodeo'] *= deg2rad;
  satrec['argpo'] *= deg2rad;
  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;
  }

  final mdhmsResult = days2mdhms(year, satrec['epochdays']);

  final mon = mdhmsResult.mon;
  final day = mdhmsResult.day;
  final hr = mdhmsResult.hr;
  final minute = mdhmsResult.minute;
  final sec = mdhmsResult.sec;
  satrec['jdsatepoch'] = jday(year, mon, day, hr, minute, sec);

  //  ---------------- initialize the orbit at sgp4epoch -------------------
  sgp4init(satrec, {
    'opsmode': opsmode,
    'satn': satrec['satnum'],
    'epoch': satrec['jdsatepoch'] - 2433281.5,
    'xbstar': satrec['bstar'],
    'xecco': satrec['ecco'],
    'xargpo': satrec['argpo'],
    'xinclo': satrec['inclo'],
    'xmo': satrec['mo'],
    'xno': satrec['no'],
    'xnodeo': satrec['nodeo'],
  });

  return satrec;
}