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sgp4
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sgp4/SGDP4.cpp

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#include "SGDP4.h"
#include "SatelliteException.h"
#include <math.h>
SGDP4::SGDP4(void) {
first_run_ = true;
}
SGDP4::~SGDP4(void) {
}
void SGDP4::Initialize(const Tle& tle) {
/*
* extract and format tle data
*/
tle_data_.bstar = tle.GetField(Tle::FLD_BSTAR);
tle_data_.eo = tle.GetField(Tle::FLD_E);
tle_data_.omega = tle.GetField(Tle::FLD_ARGPER, Tle::U_RAD);
tle_data_.xincl = tle.GetField(Tle::FLD_I, Tle::U_RAD);
tle_data_.xmo = tle.GetField(Tle::FLD_M, Tle::U_RAD);
tle_data_.xno = tle.GetField(Tle::FLD_MMOTION) / (1440.0 / Globals::TWOPI());
tle_data_.xnodeo = tle.GetField(Tle::FLD_RAAN, Tle::U_RAD);
/*
* generate julian date for tle epoch
*/
int year = static_cast<int> (tle.GetField(Tle::FLD_EPOCHYEAR));
if (year < 57)
year += 2000;
else
year += 1900;
double day = tle.GetField(Tle::FLD_EPOCHDAY);
Julian jul(year, day);
tle_data_.epoch = jul;
double cosio_ = 0.0;
double sinio_ = 0.0;
double betao2_ = 0.0;
double betao_ = 0.0;
double xnodp_ = 0.0;
double aodp_ = 0.0;
double gsto = 0.0;
bool use_simple_model_ = false;
bool use_deep_space_ = false;
/*
* recover original mean motion (xnodp) and semimajor axis (aodp)
* from input elements
*/
double a1 = pow(Globals::XKE() / tle_data_.xno, Globals::TOTHRD());
cosio_ = cos(tle_data_.xincl);
sinio_ = sin(tle_data_.xincl);
double theta2 = cosio_ * cosio_;
double x3thm1 = 3.0 * theta2 - 1.0;
double eosq = tle_data_.eo * tle_data_.eo;
betao2_ = 1.0 - eosq;
betao_ = sqrt(betao2_);
double del1 = 1.5 * Globals::CK2() * x3thm1 / (a1 * a1 * betao_ * betao2_);
double ao = a1 * (1.0 - del1 * (0.5 * Globals::TOTHRD() + del1 * (1.0 + 134.0 / 81.0 * del1)));
double delo = 1.5 * Globals::CK2() * x3thm1 / (ao * ao * betao_ * betao2_);
/*
* recovered mean motion
*/
xnodp_ = tle_data_.xno / (1.0 + delo);
/*
* recovered semimajor axis
*/
aodp_ = ao / (1.0 - delo);
gsto = tle_data_.epoch.ToGMST();
double rp = aodp_ * (1.0 - tle_data_.eo);
double perigee = (aodp_ * (1.0 - tle_data_.eo) - Globals::AE()) * Globals::XKMPER();
double period = Globals::TWOPI() / xnodp_;
/*
* for perigee less than 220 kilometers, the simple_model flag is set and
* the equations are truncated to linear variation in sqrt a and
* quadratic variation in mean anomly. also, the c3 term, the
* delta omega term and the delta m term are dropped
*/
use_simple_model_ = false;
if (rp < (220.0 / Globals::XKMPER() + Globals::AE()))
use_simple_model_ = true;
double s4_ = 0.0;
double qoms24_ = 0.0;
s4_ = Globals::S();
qoms24_ = Globals::QOMS2T();
/*
* for perigee below 156km, the values of
* s4 and qoms2t are altered
*/
if (perigee < 156.0) {
s4_ = perigee - 78.0;
if (perigee <= 98.0) {
s4_ = 20.0;
}
qoms24_ = pow((120.0 - s4_) * Globals::AE() / Globals::XKMPER(), 4.0);
s4_ = s4_ / Globals::XKMPER() + Globals::AE();
}
if (period >= 225.0) {
use_deep_space_ = true;
}
double pinvsq = 1.0 / (aodp_ * aodp_ * betao2_ * betao2_);
double sing = sin(tle_data_.omega);
double cosg = cos(tle_data_.omega);
double tsi_ = 0.0;
double eta_ = 0.0;
double eeta_ = 0.0;
double coef_ = 0.0;
double coef1_ = 0.0;
double c1_ = 0.0;
double a3ovk2_ = 0.0;
tsi_ = 1.0 / (aodp_ - s4_);
eta_ = aodp_ * tle_data_.eo * tsi_;
double etasq = eta_ * eta_;
eeta_ = tle_data_.eo * eta_;
double psisq = fabs(1.0 - etasq);
coef_ = qoms24_ * pow(tsi_, 4.0);
coef1_ = coef_ / pow(psisq, 3.5);
double c2 = coef1_ * xnodp_ * (aodp_ * (1.0 + 1.5 * etasq + eeta_ *
(4.0 + etasq)) + 0.75 * Globals::CK2() * tsi_ / psisq *
x3thm1 * (8.0 + 3.0 * etasq * (8.0 + etasq)));
c1_ = tle_data_.bstar * c2;
a3ovk2_ = -Globals::XJ3() / Globals::CK2() * pow(Globals::AE(), 3.0);
double c3_ = 0.0;
double c4_ = 0.0;
double c5_ = 0.0;
double xmdot_ = 0.0;
double omgdot_ = 0.0;
double xnodot_ = 0.0;
double xnodcf_ = 0.0;
double t2cof_ = 0.0;
double xlcof_ = 0.0; // move to end?
double aycof_ = 0.0; // move to end?
double x7thm1_ = 0.0; // move to end?
double omgcof_ = 0.0;
double xmcof_ = 0.0;
double delmo_ = 0.0;
double sinmo_ = 0.0;
double x1mth2 = 1.0 - theta2;
c4_ = 2.0 * xnodp_ * coef1_ * aodp_ * betao2_ *
(eta_ * (2.0 + 0.5 * etasq) + tle_data_.eo * (0.5 + 2.0 * etasq) -
2.0 * Globals::CK2() * tsi_ / (aodp_ * psisq) *
(-3.0 * x3thm1 * (1.0 - 2.0 * eeta_ + etasq *
(1.5 - 0.5 * eeta_)) + 0.75 * x1mth2 * (2.0 * etasq - eeta_ *
(1.0 + etasq)) * cos(2.0 * tle_data_.omega)));
double theta4 = theta2 * theta2;
double temp1 = 3.0 * Globals::CK2() * pinvsq * xnodp_;
double temp2 = temp1 * Globals::CK2() * pinvsq;
double temp3 = 1.25 * Globals::CK4() * pinvsq * pinvsq * xnodp_;
xmdot_ = xnodp_ + 0.5 * temp1 * betao_ * x3thm1 + 0.0625 * temp2 * betao_ *
(13.0 - 78.0 * theta2 + 137.0 * theta4);
double x1m5th = 1.0 - 5.0 * theta2;
omgdot_ = -0.5 * temp1 * x1m5th + 0.0625 * temp2 * (7.0 - 114.0 * theta2 +
395.0 * theta4) + temp3 * (3.0 - 36.0 * theta2 + 49.0 * theta4);
double xhdot1_ = -temp1 * cosio_;
xnodot_ = xhdot1_ + (0.5 * temp2 * (4.0 - 19.0 * theta2) + 2.0 * temp3 *
(3.0 - 7.0 * theta2)) * cosio_;
xnodcf_ = 3.5 * betao2_ * xhdot1_ * c1_;
t2cof_ = 1.5 * c1_;
if (fabs(cosio_ + 1.0) > 1.5e-12)
xlcof_ = 0.125 * a3ovk2_ * sinio_ * (3.0 + 5.0 * cosio_) / (1.0 + cosio_);
else
xlcof_ = 0.125 * a3ovk2_ * sinio_ * (3.0 + 5.0 * cosio_) / 1.5e-12;
aycof_ = 0.25 * a3ovk2_ * sinio_;
x7thm1_ = 7.0 * theta2 - 1.0;
if (!use_deep_space_) {
// check result (different to telsko)
c3_ = 0.0;
if (tle_data_.eo > 1.0e-4)
c3_ = coef_ * tsi_ * a3ovk2_ * xnodp_ * Globals::AE() *
sinio_ / tle_data_.eo;
c5_ = 2.0 * coef1_ * aodp_ * betao2_ * (1.0 + 2.75 * (etasq + eeta_) + eeta_ * etasq);
omgcof_ = tle_data_.bstar * c3_ * cos(tle_data_.omega);
xmcof_ = 0.0;
if (tle_data_.eo > 1.0e-4)
xmcof_ = -Globals::TOTHRD() * coef_ * tle_data_.bstar * Globals::AE() / eeta_;
delmo_ = pow(1.0 + eta_ * (cos(tle_data_.xmo)), 3.0);
sinmo_ = sin(tle_data_.xmo);
}
double d2_ = 0.0;
double d3_ = 0.0;
double d4_ = 0.0;
double t3cof_ = 0.0;
double t4cof_ = 0.0;
double t5cof_ = 0.0;
if (!use_simple_model_) {
double c1sq = c1_ * c1_;
d2_ = 4.0 * aodp_ * tsi_ * c1sq;
double temp = d2_ * tsi_ * c1_ / 3.0;
d3_ = (17.0 * aodp_ + s4_) * temp;
d4_ = 0.5 * temp * aodp_ * tsi_ * (221.0 * aodp_ + 31.0 * s4_) * c1_;
t3cof_ = d2_ + 2.0 * c1sq;
t4cof_ = 0.25 * (3.0 * d3_ + c1_ * (12.0 * d2_ + 10.0 * c1sq));
t5cof_ = 0.2 * (3.0 * d4_ + 12.0 * c1_ * d3_ + 6.0 * d2_ * d2_ + 15.0 *
c1sq * (2.0 * d2_ + c1sq));
} else if (use_deep_space_) {
}
first_run_ = false;
}
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