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gnss-sdr/src/core/system_parameters/beidou_dnav_ephemeris.cc

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/*!
* \file beidou_ephemeris.cc
* \brief Interface of a BeiDou EPHEMERIS storage and orbital model functions
*
* \author Sergi Segura, 2018. sergi.segura.munoz(at)gmail.com
*
* -------------------------------------------------------------------------
*
* Copyright (C) 2010-2015 (see AUTHORS file for a list of contributors)
*
* GNSS-SDR is a software defined Global Navigation
* Satellite Systems receiver
*
* This file is part of GNSS-SDR.
*
* GNSS-SDR is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* GNSS-SDR is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNSS-SDR. If not, see <http://www.gnu.org/licenses/>.
*
* -------------------------------------------------------------------------
*/
#include "beidou_dnav_ephemeris.h"
#include "Beidou_B1I.h"
#include "gnss_satellite.h"
#include <cmath>
Beidou_Dnav_Ephemeris::Beidou_Dnav_Ephemeris()
{
i_satellite_PRN = 0;
d_TOW = 0;
d_Crs = 0;
d_Delta_n = 0;
d_M_0 = 0;
d_Cuc = 0;
d_eccentricity = 0;
d_Cus = 0;
d_sqrt_A = 0;
d_Toe = 0;
d_Toc = 0;
d_Cic = 0;
d_OMEGA0 = 0;
d_Cis = 0;
d_i_0 = 0;
d_Crc = 0;
d_OMEGA = 0;
d_OMEGA_DOT = 0;
d_IDOT = 0;
i_BEIDOU_week = 0;
i_SV_accuracy = 0;
i_SV_health = 0;
d_AODE = 0;
d_TGD1 = 0;
d_TGD2 = 0;
d_AODC = 0; // Issue of Data, Clock
i_AODO = 0; // Age of Data Offset (AODO) term for the navigation message correction table (NMCT) contained in subframe 4 (reference paragraph 20.3.3.5.1.9) [s]
d_AODC = 0;
b_fit_interval_flag = false; // indicates the curve-fit interval used by the CS (Block II/IIA/IIR/IIR-M/IIF) and SS (Block IIIA) in determining the ephemeris parameters, as follows: 0 = 4 hours, 1 = greater than 4 hours.
d_spare1 = 0;
d_spare2 = 0;
i_sig_type = 0;
i_nav_type = 0;
d_A_f0 = 0; // Coefficient 0 of code phase offset model [s]
d_A_f1 = 0; // Coefficient 1 of code phase offset model [s/s]
d_A_f2 = 0; // Coefficient 2 of code phase offset model [s/s^2]
b_integrity_status_flag = false;
b_alert_flag = false; // If true, indicates that the SV URA may be worse than indicated in d_SV_accuracy, use that SV at our own risk.
b_antispoofing_flag = false; // If true, the AntiSpoofing mode is ON in that SV
auto gnss_sat = Gnss_Satellite();
std::string _system("Beidou");
for (unsigned int i = 1; i < 36; i++)
{
satelliteBlock[i] = gnss_sat.what_block(_system, i);
}
d_satClkDrift = 0.0;
d_dtr = 0.0;
d_satpos_X = 0.0;
d_satpos_Y = 0.0;
d_satpos_Z = 0.0;
d_satvel_X = 0.0;
d_satvel_Y = 0.0;
d_satvel_Z = 0.0;
}
double Beidou_Dnav_Ephemeris::check_t(double time)
{
double corrTime;
double half_week = 302400.0; // seconds
corrTime = time;
if (time > half_week)
{
corrTime = time - 2.0 * half_week;
}
else if (time < -half_week)
{
corrTime = time + 2.0 * half_week;
}
return corrTime;
}
// 20.3.3.3.3.1 User Algorithm for SV Clock Correction.
double Beidou_Dnav_Ephemeris::sv_clock_drift(double transmitTime)
{
double dt;
dt = check_t(transmitTime - d_Toc);
for (int i = 0; i < 2; i++)
{
dt -= d_A_f0 + d_A_f1 * dt + d_A_f2 * (dt * dt);
}
d_satClkDrift = d_A_f0 + d_A_f1 * dt + d_A_f2 * (dt * dt);
return d_satClkDrift;
}
// compute the relativistic correction term
double Beidou_Dnav_Ephemeris::sv_clock_relativistic_term(double transmitTime)
{
double tk;
double a;
double n;
double n0;
double E;
double E_old;
double dE;
double M;
// Restore semi-major axis
a = d_sqrt_A * d_sqrt_A;
// Time from ephemeris reference epoch
tk = check_t(transmitTime - d_Toe);
// Computed mean motion
n0 = sqrt(BEIDOU_GM / (a * a * a));
// Corrected mean motion
n = n0 + d_Delta_n;
// Mean anomaly
M = d_M_0 + n * tk;
// Reduce mean anomaly to between 0 and 2pi
M = fmod((M + 2.0 * BEIDOU_PI), (2.0 * BEIDOU_PI));
// Initial guess of eccentric anomaly
E = M;
// --- Iteratively compute eccentric anomaly ----------------------------
for (int ii = 1; ii < 20; ii++)
{
E_old = E;
E = M + d_eccentricity * sin(E);
dE = fmod(E - E_old, 2.0 * BEIDOU_PI);
if (fabs(dE) < 1e-12)
{
//Necessary precision is reached, exit from the loop
break;
}
}
// Compute relativistic correction term
d_dtr = BEIDOU_F * d_eccentricity * d_sqrt_A * sin(E);
return d_dtr;
}
double Beidou_Dnav_Ephemeris::satellitePosition(double transmitTime)
{
double tk;
double a;
double n;
double n0;
double M;
double E;
double E_old;
double dE;
double nu;
double phi;
double u;
double r;
double i;
double Omega;
// Find satellite's position ----------------------------------------------
// Restore semi-major axis
a = d_sqrt_A * d_sqrt_A;
// Time from ephemeris reference epoch
tk = check_t(transmitTime - d_Toe);
// Computed mean motion
n0 = sqrt(BEIDOU_GM / (a * a * a));
// Corrected mean motion
n = n0 + d_Delta_n;
// Mean anomaly
M = d_M_0 + n * tk;
// Reduce mean anomaly to between 0 and 2pi
M = fmod((M + 2.0 * BEIDOU_PI), (2.0 * BEIDOU_PI));
// Initial guess of eccentric anomaly
E = M;
// --- Iteratively compute eccentric anomaly ----------------------------
for (int ii = 1; ii < 20; ii++)
{
E_old = E;
E = M + d_eccentricity * sin(E);
dE = fmod(E - E_old, 2.0 * BEIDOU_PI);
if (fabs(dE) < 1e-12)
{
//Necessary precision is reached, exit from the loop
break;
}
}
// Compute the true anomaly
double tmp_Y = sqrt(1.0 - d_eccentricity * d_eccentricity) * sin(E);
double tmp_X = cos(E) - d_eccentricity;
nu = atan2(tmp_Y, tmp_X);
// Compute angle phi (argument of Latitude)
phi = nu + d_OMEGA;
// Reduce phi to between 0 and 2*pi rad
phi = fmod((phi), (2.0 * BEIDOU_PI));
// Correct argument of latitude
u = phi + d_Cuc * cos(2.0 * phi) + d_Cus * sin(2.0 * phi);
// Correct radius
r = a * (1.0 - d_eccentricity * cos(E)) + d_Crc * cos(2.0 * phi) + d_Crs * sin(2.0 * phi);
// Correct inclination
i = d_i_0 + d_IDOT * tk + d_Cic * cos(2.0 * phi) + d_Cis * sin(2.0 * phi);
// Compute the angle between the ascending node and the Greenwich meridian
Omega = d_OMEGA0 + (d_OMEGA_DOT - BEIDOU_OMEGA_EARTH_DOT) * tk - BEIDOU_OMEGA_EARTH_DOT * d_Toe;
// Reduce to between 0 and 2*pi rad
Omega = fmod((Omega + 2.0 * BEIDOU_PI), (2.0 * BEIDOU_PI));
// --- Compute satellite coordinates in Earth-fixed coordinates
d_satpos_X = cos(u) * r * cos(Omega) - sin(u) * r * cos(i) * sin(Omega);
d_satpos_Y = cos(u) * r * sin(Omega) + sin(u) * r * cos(i) * cos(Omega);
d_satpos_Z = sin(u) * r * sin(i);
// Satellite's velocity. Can be useful for Vector Tracking loops
double Omega_dot = d_OMEGA_DOT - BEIDOU_OMEGA_EARTH_DOT;
d_satvel_X = -Omega_dot * (cos(u) * r + sin(u) * r * cos(i)) + d_satpos_X * cos(Omega) - d_satpos_Y * cos(i) * sin(Omega);
d_satvel_Y = Omega_dot * (cos(u) * r * cos(Omega) - sin(u) * r * cos(i) * sin(Omega)) + d_satpos_X * sin(Omega) + d_satpos_Y * cos(i) * cos(Omega);
d_satvel_Z = d_satpos_Y * sin(i);
// Time from ephemeris reference clock
tk = check_t(transmitTime - d_Toc);
double dtr_s = d_A_f0 + d_A_f1 * tk + d_A_f2 * tk * tk;
/* relativity correction */
dtr_s -= 2.0 * sqrt(BEIDOU_GM * a) * d_eccentricity * sin(E) / (BEIDOU_C_m_s * BEIDOU_C_m_s);
return dtr_s;
}
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