TCB top-level property

TimeInstantUnits TCB

Barycentric Coordinate Time (TCB): TCB = TDB + (1.550505e-8)(JD - 2443144.5)(86400)

Implementation

// ignore: non_constant_identifier_names
final TimeInstantUnits TCB = TimeInstantUnits(
    'Barycentric Coordinate Time', null, 'TCB', null, 1.0 - 1.550505e-8, false, 599616000.0 - 32.184, (dynamic val) {
  final d = val is num
      ? val.toDouble()
      : val is Number
          ? val.toDouble()
          : 0.0;
  var tdb = TDB.fromMks(val); // TDB seconds
  return tdb += 1.550505e-8 * (d - 5.99616e8);
}, (dynamic val) {
  final d = val is num
      ? val.toDouble()
      : val is Number
          ? val.toDouble()
          : 0.0;

  // Too convoluted to solve analytically... instead, get close and then search
  var taiTest = d;
  var step = 10.0;
  const epsilon = 1.0e-8;
  const maxCount = 10000;
  var count = 0;
  var tcbTest = TCB.fromMks(d).toDouble();
  var delta = tcbTest - taiTest;
  var prevDelta = double.maxFinite;
  while ((delta.abs() > epsilon) && (count < maxCount)) {
    // See if we got farther away (if so reverse and take smaller steps)
    if (delta.abs() > prevDelta.abs()) step *= -0.5;

    // Step
    taiTest += step;

    prevDelta = delta;
    count++;

    // value & delta
    tcbTest = TCB.fromMks(taiTest).toDouble();
    delta = tcbTest - d;
  }

  // taiTest now returns a tcb value within epsilon (or loop count ran out)
  return Double(taiTest);
});