Implementation
void sgp4init(Map<String, dynamic> satrec, Map<String, dynamic> options) {
/* eslint-disable no-param-reassign */
final opsmode = options['opsmode'];
final satn = options['satn'];
final epoch = options['epoch'];
final xbstar = options['xbstar'];
final xecco = options['xecco'];
final xargpo = options['xargpo'];
final xinclo = options['xinclo'];
final xmo = options['xmo'];
final xno = options['xno'];
final xnodeo = options['xnodeo'];
var cosim;
var sinim;
var cc1sq;
var cc2;
var cc3;
var coef;
var coef1;
var cosio4;
var em;
var emsq;
var eeta;
var etasq;
var argpm;
var nodem;
var inclm;
var mm;
var nm;
var perige;
var pinvsq;
var psisq;
var qzms24;
var s1;
var s2;
var s3;
var s4;
var s5;
var sfour;
var ss1;
var ss2;
var ss3;
var ss4;
var ss5;
var sz1;
var sz3;
var sz11;
var sz13;
var sz21;
var sz23;
var sz31;
var sz33;
var tc;
var temp;
var temp1;
var temp2;
var temp3;
var tsi;
var xpidot;
var xhdot1;
var z1;
var z3;
var z11;
var z13;
var z21;
var z23;
var z31;
var z33;
/* ------------------------ initialization --------------------- */
// sgp4fix divisor for divide by zero check on inclination
// the old check used 1.0 + Math.cos(pi-1.0e-9), but then compared it to
// 1.5 e-12, so the threshold was changed to 1.5e-12 for consistency
final temp4 = 1.5e-12;
// ----------- set all near earth variables to zero ------------
satrec['isimp'] = 0; satrec['method'] = 'n'; satrec['aycof'] = 0.0;
satrec['con41'] = 0.0; satrec['cc1'] = 0.0; satrec['cc4'] = 0.0;
satrec['cc5'] = 0.0; satrec['d2'] = 0.0; satrec['d3'] = 0.0;
satrec['d4'] = 0.0; satrec['delmo'] = 0.0; satrec['eta'] = 0.0;
satrec['argpdot'] = 0.0; satrec['omgcof'] = 0.0; satrec['sinmao'] = 0.0;
satrec['t'] = 0.0; satrec['t2cof'] = 0.0; satrec['t3cof'] = 0.0;
satrec['t4cof'] = 0.0; satrec['t5cof'] = 0.0; satrec['x1mth2'] = 0.0;
satrec['x7thm1'] = 0.0; satrec['mdot'] = 0.0; satrec['nodedot'] = 0.0;
satrec['xlcof'] = 0.0; satrec['xmcof'] = 0.0; satrec['nodecf'] = 0.0;
// ----------- set all deep space variables to zero ------------
satrec['irez'] = 0; satrec['d2201'] = 0.0; satrec['d2211'] = 0.0;
satrec['d3210'] = 0.0; satrec['d3222'] = 0.0; satrec['d4410'] = 0.0;
satrec['d4422'] = 0.0; satrec['d5220'] = 0.0; satrec['d5232'] = 0.0;
satrec['d5421'] = 0.0; satrec['d5433'] = 0.0; satrec['dedt'] = 0.0;
satrec['del1'] = 0.0; satrec['del2'] = 0.0; satrec['del3'] = 0.0;
satrec['didt'] = 0.0; satrec['dmdt'] = 0.0; satrec['dnodt'] = 0.0;
satrec['domdt'] = 0.0; satrec['e3'] = 0.0; satrec['ee2'] = 0.0;
satrec['peo'] = 0.0; satrec['pgho'] = 0.0; satrec['pho'] = 0.0;
satrec['pinco'] = 0.0; satrec['plo'] = 0.0; satrec['se2'] = 0.0;
satrec['se3'] = 0.0; satrec['sgh2'] = 0.0; satrec['sgh3'] = 0.0;
satrec['sgh4'] = 0.0; satrec['sh2'] = 0.0; satrec['sh3'] = 0.0;
satrec['si2'] = 0.0; satrec['si3'] = 0.0; satrec['sl2'] = 0.0;
satrec['sl3'] = 0.0; satrec['sl4'] = 0.0; satrec['gsto'] = 0.0;
satrec['xfact'] = 0.0; satrec['xgh2'] = 0.0; satrec['xgh3'] = 0.0;
satrec['xgh4'] = 0.0; satrec['xh2'] = 0.0; satrec['xh3'] = 0.0;
satrec['xi2'] = 0.0; satrec['xi3'] = 0.0; satrec['xl2'] = 0.0;
satrec['xl3'] = 0.0; satrec['xl4'] = 0.0; satrec['xlamo'] = 0.0;
satrec['zmol'] = 0.0; satrec['zmos'] = 0.0; satrec['atime'] = 0.0;
satrec['xli'] = 0.0; satrec['xni'] = 0.0;
// sgp4fix - note the following variables are also passed directly via satrec.
// it is possible to streamline the sgp4init call by devaring the "x"
// variables, but the user would need to set the satrec.* values first. we
// include the additional assignments in case twoline2rv is not used.
satrec['bstar'] = xbstar;
satrec['ecco'] = xecco;
satrec['argpo'] = xargpo;
satrec['inclo'] = xinclo;
satrec['mo'] = xmo;
satrec['no'] = xno;
satrec['nodeo'] = xnodeo;
// sgp4fix add opsmode
satrec['operationmode'] = opsmode;
// ------------------------ earth finalants -----------------------
// sgp4fix identify finalants and allow alternate values
final ss = (78.0 / earthRadius) + 1.0;
// sgp4fix use multiply for speed instead of pow
final qzms2ttemp = (120.0 - 78.0) / earthRadius;
final qzms2t = qzms2ttemp * qzms2ttemp * qzms2ttemp * qzms2ttemp;
satrec['init'] = 'y';
satrec['t'] = 0.0;
final initlOptions = {
'satn': satn,
'ecco': satrec['ecco'],
'epoch': epoch,
'inclo': satrec['inclo'],
'no': satrec['no'],
'method': satrec['method'],
'opsmode': satrec['operationmode'],
};
final initlResult = initl(initlOptions);
final ao = initlResult['ao'];
final con42 = initlResult['con42'];
final cosio = initlResult['cosio'];
final cosio2 = initlResult['cosio2'];
final eccsq = initlResult['eccsq'];
final omeosq = initlResult['omeosq'];
final posq = initlResult['posq'];
final rp = initlResult['rp'];
final rteosq = initlResult['rteosq'];
final sinio = initlResult['sinio'];
satrec['no'] = initlResult['no'];
satrec['con41'] = initlResult['con41'];
satrec['gsto'] = initlResult['gsto'];
satrec['error'] = 0;
// sgp4fix remove this check as it is unnecessary
// the mrt check in sgp4 handles decaying satellite cases even if the starting
// condition is below the surface of te earth
// if (rp < 1.0)
// {
// printf("// *** satn%d epoch elts sub-orbital ***\n", satn);
// satrec['error'] = 5;
// }
if (omeosq >= 0.0 || satrec['no'] >= 0.0) {
satrec['isimp'] = 0;
if (rp < (220.0 / earthRadius + 1.0)) {
satrec['isimp'] = 1;
}
sfour = ss;
qzms24 = qzms2t;
perige = (rp - 1.0) * earthRadius;
// - for perigees below 156 km, s and qoms2t are altered -
if (perige < 156.0) {
sfour = perige - 78.0;
if (perige < 98.0) {
sfour = 20.0;
}
// sgp4fix use multiply for speed instead of pow
final qzms24temp = (120.0 - sfour) / earthRadius;
qzms24 = qzms24temp * qzms24temp * qzms24temp * qzms24temp;
sfour = (sfour / earthRadius) + 1.0;
}
pinvsq = 1.0 / posq;
tsi = 1.0 / (ao - sfour);
satrec['eta'] = ao * satrec['ecco'] * tsi;
etasq = satrec['eta'] * satrec['eta'];
eeta = satrec['ecco'] * satrec['eta'];
psisq = abs(1.0 - etasq);
coef = qzms24 * Math.pow(tsi, 4.0);
coef1 = coef / Math.pow(psisq, 3.5);
cc2 = coef1 * satrec['no'] * ((ao * (1.0 + (1.5 * etasq) + (eeta * (4.0 + etasq))))
+ (((0.375 * j2 * tsi) / psisq) * satrec['con41']
* (8.0 + (3.0 * etasq * (8.0 + etasq)))));
satrec['cc1'] = satrec['bstar'] * cc2;
cc3 = 0.0;
if (satrec['ecco'] > 1.0e-4) {
cc3 = (-2.0 * coef * tsi * j3oj2 * satrec['no'] * sinio) / satrec['ecco'];
}
satrec['x1mth2'] = 1.0 - cosio2;
satrec['cc4'] = 2.0 * satrec['no'] * coef1 * ao * omeosq * (
((satrec['eta'] * (2.0 + (0.5 * etasq)))
+ (satrec['ecco'] * (0.5 + (2.0 * etasq))))
- (((j2 * tsi) / (ao * psisq))
* ((-3.0 * satrec['con41'] * ((1.0 - (2.0 * eeta)) + (etasq * (1.5 - (0.5 * eeta)))))
+ (0.75 * satrec['x1mth2']
* ((2.0 * etasq) - (eeta * (1.0 + etasq)))
* Math.cos(2.0 * satrec['argpo']))))
);
satrec['cc5'] = 2.0 * coef1 * ao * omeosq * (1.0 + (2.75 * (etasq + eeta)) + (eeta * etasq));
cosio4 = cosio2 * cosio2;
temp1 = 1.5 * j2 * pinvsq * satrec['no'];
temp2 = 0.5 * temp1 * j2 * pinvsq;
temp3 = -0.46875 * j4 * pinvsq * pinvsq * satrec['no'];
satrec['mdot'] = satrec['no'] + (0.5 * temp1 * rteosq * satrec['con41'])
+ (0.0625 * temp2 * rteosq * ((13.0 - (78.0 * cosio2)) + (137.0 * cosio4)));
satrec['argpdot'] = (-0.5 * temp1 * con42)
+ (0.0625 * temp2 * ((7.0 - (114.0 * cosio2)) + (395.0 * cosio4)))
+ (temp3 * ((3.0 - (36.0 * cosio2)) + (49.0 * cosio4)));
xhdot1 = -temp1 * cosio;
satrec['nodedot'] = xhdot1 + (((0.5 * temp2 * (4.0 - (19.0 * cosio2)))
+ (2.0 * temp3 * (3.0 - (7.0 * cosio2)))) * cosio);
xpidot = satrec['argpdot'] + satrec['nodedot'];
satrec['omgcof'] = satrec['bstar'] * cc3 * Math.cos(satrec['argpo']);
satrec['xmcof'] = 0.0;
if (satrec['ecco'] > 1.0e-4) {
satrec['xmcof'] = (-x2o3 * coef * satrec['bstar']) / eeta;
}
satrec['nodecf'] = 3.5 * omeosq * xhdot1 * satrec['cc1'];
satrec['t2cof'] = 1.5 * satrec['cc1'];
// sgp4fix for divide by zero with xinco = 180 deg
if (abs(cosio + 1.0) > 1.5e-12) {
satrec['xlcof'] = (-0.25 * j3oj2 * sinio * (3.0 + (5.0 * cosio))) / (1.0 + cosio);
} else {
satrec['xlcof'] = (-0.25 * j3oj2 * sinio * (3.0 + (5.0 * cosio))) / temp4;
}
satrec['aycof'] = -0.5 * j3oj2 * sinio;
// sgp4fix use multiply for speed instead of pow
final delmotemp = 1.0 + (satrec['eta'] * Math.cos(satrec['mo']));
satrec['delmo'] = delmotemp * delmotemp * delmotemp;
satrec['sinmao'] = Math.sin(satrec['mo']);
satrec['x7thm1'] = (7.0 * cosio2) - 1.0;
// --------------- deep space initialization -------------
if ((2 * pi) / satrec['no'] >= 225.0) {
satrec['method'] = 'd';
satrec['isimp'] = 1;
tc = 0.0;
inclm = satrec['inclo'];
final dscomOptions = {
'epoch': epoch,
'ep': satrec['ecco'],
'argpp': satrec['argpo'],
'tc': tc,
'inclp': satrec['inclo'],
'nodep': satrec['nodeo'],
'np': satrec['no'],
'e3': satrec['e3'],
'ee2': satrec['ee2'],
'peo': satrec['peo'],
'pgho': satrec['pgho'],
'pho': satrec['pho'],
'pinco': satrec['pinco'],
'plo': satrec['plo'],
'se2': satrec['se2'],
'se3': satrec['se3'],
'sgh2': satrec['sgh2'],
'sgh3': satrec['sgh3'],
'sgh4': satrec['sgh4'],
'sh2': satrec['sh2'],
'sh3': satrec['sh3'],
'si2': satrec['si2'],
'si3': satrec['si3'],
'sl2': satrec['sl2'],
'sl3': satrec['sl3'],
'sl4': satrec['sl4'],
'xgh2': satrec['xgh2'],
'xgh3': satrec['xgh3'],
'xgh4': satrec['xgh4'],
'xh2': satrec['xh2'],
'xh3': satrec['xh3'],
'xi2': satrec['xi2'],
'xi3': satrec['xi3'],
'xl2': satrec['xl2'],
'xl3': satrec['xl3'],
'xl4': satrec['xl4'],
'zmol': satrec['zmol'],
'zmos': satrec['zmos'],
};
final dscomResult = dscom(dscomOptions);
satrec['e3'] = dscomResult['e3'];
satrec['ee2'] = dscomResult['ee2'];
satrec['peo'] = dscomResult['peo'];
satrec['pgho'] = dscomResult['pgho'];
satrec['pho'] = dscomResult['pho'];
satrec['pinco'] = dscomResult['pinco'];
satrec['plo'] = dscomResult['plo'];
satrec['se2'] = dscomResult['se2'];
satrec['se3'] = dscomResult['se3'];
satrec['sgh2'] = dscomResult['sgh2'];
satrec['sgh3'] = dscomResult['sgh3'];
satrec['sgh4'] = dscomResult['sgh4'];
satrec['sh2'] = dscomResult['sh2'];
satrec['sh3'] = dscomResult['sh3'];
satrec['si2'] = dscomResult['si2'];
satrec['si3'] = dscomResult['si3'];
satrec['sl2'] = dscomResult['sl2'];
satrec['sl3'] = dscomResult['sl3'];
satrec['sl4'] = dscomResult['sl4'];
sinim = dscomResult['sinim'];
cosim = dscomResult['cosim'];
em = dscomResult['em'];
emsq = dscomResult['emsq'];
s1 = dscomResult['s1'];
s2 = dscomResult['s2'];
s3 = dscomResult['s3'];
s4 = dscomResult['s4'];
s5 = dscomResult['s5'];
ss1 = dscomResult['ss1'];
ss2 = dscomResult['ss2'];
ss3 = dscomResult['ss3'];
ss4 = dscomResult['ss4'];
ss5 = dscomResult['ss5'];
sz1 = dscomResult['sz1'];
sz3 = dscomResult['sz3'];
sz11 = dscomResult['sz11'];
sz13 = dscomResult['sz13'];
sz21 = dscomResult['sz21'];
sz23 = dscomResult['sz23'];
sz31 = dscomResult['sz31'];
sz33 = dscomResult['sz33'];
satrec['xgh2'] = dscomResult['xgh2'];
satrec['xgh3'] = dscomResult['xgh3'];
satrec['xgh4'] = dscomResult['xgh4'];
satrec['xh2'] = dscomResult['xh2'];
satrec['xh3'] = dscomResult['xh3'];
satrec['xi2'] = dscomResult['xi2'];
satrec['xi3'] = dscomResult['xi3'];
satrec['xl2'] = dscomResult['xl2'];
satrec['xl3'] = dscomResult['xl3'];
satrec['xl4'] = dscomResult['xl4'];
satrec['zmol'] = dscomResult['zmol'];
satrec['zmos'] = dscomResult['zmos'];
nm = dscomResult['nm'];
z1 = dscomResult['z1'];
z3 = dscomResult['z3'];
z11 = dscomResult['z11'];
z13 = dscomResult['z13'];
z21 = dscomResult['z21'];
z23 = dscomResult['z23'];
z31 = dscomResult['z31'];
z33 = dscomResult['z33'];
final dpperOptions = {
'inclo': inclm,
'init': satrec['init'],
'ep': satrec['ecco'],
'inclp': satrec['inclo'],
'nodep': satrec['nodeo'],
'argpp': satrec['argpo'],
'mp': satrec['mo'],
'opsmode': satrec['operationmode'],
};
final dpperResult = dpper(satrec, dpperOptions);
satrec['ecco'] = dpperResult['ep'];
satrec['inclo'] = dpperResult['inclp'];
satrec['nodeo'] = dpperResult['nodep'];
satrec['argpo'] = dpperResult['argpp'];
satrec['mo'] = dpperResult['mp'];
argpm = 0.0;
nodem = 0.0;
mm = 0.0;
final dsinitOptions = {
'cosim': cosim,
'emsq': emsq,
'argpo': satrec['argpo'],
's1': s1,
's2': s2,
's3': s3,
's4': s4,
's5': s5,
'sinim': sinim,
'ss1': ss1,
'ss2': ss2,
'ss3': ss3,
'ss4': ss4,
'ss5': ss5,
'sz1': sz1,
'sz3': sz3,
'sz11': sz11,
'sz13': sz13,
'sz21': sz21,
'sz23': sz23,
'sz31': sz31,
'sz33': sz33,
't': satrec['t'],
'tc': tc,
'gsto': satrec['gsto'],
'mo': satrec['mo'],
'mdot': satrec['mdot'],
'no': satrec['no'],
'nodeo': satrec['nodeo'],
'nodedot': satrec['nodedot'],
'xpidot': xpidot,
'z1': z1,
'z3': z3,
'z11': z11,
'z13': z13,
'z21': z21,
'z23': z23,
'z31': z31,
'z33': z33,
'ecco': satrec['ecco'],
'eccsq': eccsq,
'em': em,
'argpm': argpm,
'inclm': inclm,
'mm': mm,
'nm': nm,
'nodem': nodem,
'irez': satrec['irez'],
'atime': satrec['atime'],
'd2201': satrec['d2201'],
'd2211': satrec['d2211'],
'd3210': satrec['d3210'],
'd3222': satrec['d3222'],
'd4410': satrec['d4410'],
'd4422': satrec['d4422'],
'd5220': satrec['d5220'],
'd5232': satrec['d5232'],
'd5421': satrec['d5421'],
'd5433': satrec['d5433'],
'dedt': satrec['dedt'],
'didt': satrec['didt'],
'dmdt': satrec['dmdt'],
'dnodt': satrec['dnodt'],
'domdt': satrec['domdt'],
'del1': satrec['del1'],
'del2': satrec['del2'],
'del3': satrec['del3'],
'xfact': satrec['xfact'],
'xlamo': satrec['xlamo'],
'xli': satrec['xli'],
'xni': satrec['xni'],
};
final dsinitResult = dsinit(dsinitOptions);
satrec['irez'] = dsinitResult['irez'];
satrec['atime'] = dsinitResult['atime'];
satrec['d2201'] = dsinitResult['d2201'];
satrec['d2211'] = dsinitResult['d2211'];
satrec['d3210'] = dsinitResult['d3210'];
satrec['d3222'] = dsinitResult['d3222'];
satrec['d4410'] = dsinitResult['d4410'];
satrec['d4422'] = dsinitResult['d4422'];
satrec['d5220'] = dsinitResult['d5220'];
satrec['d5232'] = dsinitResult['d5232'];
satrec['d5421'] = dsinitResult['d5421'];
satrec['d5433'] = dsinitResult['d5433'];
satrec['dedt'] = dsinitResult['dedt'];
satrec['didt'] = dsinitResult['didt'];
satrec['dmdt'] = dsinitResult['dmdt'];
satrec['dnodt'] = dsinitResult['dnodt'];
satrec['domdt'] = dsinitResult['domdt'];
satrec['del1'] = dsinitResult['del1'];
satrec['del2'] = dsinitResult['del2'];
satrec['del3'] = dsinitResult['del3'];
satrec['xfact'] = dsinitResult['xfact'];
satrec['xlamo'] = dsinitResult['xlamo'];
satrec['xli'] = dsinitResult['xli'];
satrec['xni'] = dsinitResult['xni'];
}
// ----------- set variables if not deep space -----------
if (satrec['isimp'] != 1) {
cc1sq = satrec['cc1'] * satrec['cc1'];
satrec['d2'] = 4.0 * ao * tsi * cc1sq;
temp = (satrec['d2'] * tsi * satrec['cc1']) / 3.0;
satrec['d3'] = ((17.0 * ao) + sfour) * temp;
satrec['d4'] = 0.5 * temp * ao * tsi * ((221.0 * ao) + (31.0 * sfour)) * satrec['cc1'];
satrec['t3cof'] = satrec['d2'] + (2.0 * cc1sq);
satrec['t4cof'] = 0.25 * ((3.0 * satrec['d3'])
+ (satrec['cc1'] * ((12.0 * satrec['d2']) + (10.0 * cc1sq))));
satrec['t5cof'] = 0.2 * (
(3.0 * satrec['d4'])
+ (12.0 * satrec['cc1'] * satrec['d3'])
+ (6.0 * satrec['d2'] * satrec['d2'])
+ (15.0 * cc1sq * ((2.0 * satrec['d2']) + cc1sq))
);
}
/* finally propogate to zero epoch to initialize all others. */
// sgp4fix take out check to var satellites process until they are actually below earth surface
// if(satrec['error'] == 0)
}
sgp4(satrec, 0);
satrec['init'] = 'n';
/* eslint-enable no-param-reassign */
}
