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Add a Doppler prediction method to Ephemeris objects
This commit is contained in:
Carles Fernandez
parent
feaab97c3d
commit
9af3e6c125
@ -17,10 +17,156 @@
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#include "gnss_ephemeris.h"
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#include "MATH_CONSTANTS.h"
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#include "gnss_frequencies.h"
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#include <algorithm>
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#include <cmath>
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#include <functional>
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#include <numeric>
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#include <vector>
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double Gnss_Ephemeris::sv_clock_drift(double transmitTime)
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{
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const double dt = check_t(transmitTime - this->toc);
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this->dtr = sv_clock_relativistic_term(transmitTime);
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this->satClkDrift = this->af0 + this->af1 * dt + this->af2 * (dt * dt) + this->dtr;
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return this->satClkDrift;
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}
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double Gnss_Ephemeris::predicted_doppler(double rx_time_s,
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double lat,
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double lon,
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double h,
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double ve,
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double vn,
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double vu,
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int band) const
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{
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const double RE_WGS84 = 6378137.0; //!< earth semimajor axis (WGS84) (m)
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const double FE_WGS84 = (1.0 / 298.257223563); //!< earth flattening (WGS84)
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const double lat_rad = lat * D2R;
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const double lon_rad = lon * D2R;
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const double sinp = sin(lat_rad);
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const double cosp = cos(lat_rad);
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const double sinl = sin(lon_rad);
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const double cosl = cos(lon_rad);
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const double e2 = FE_WGS84 * (2.0 - FE_WGS84);
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const double v = RE_WGS84 / std::sqrt(1.0 - e2 * sinp * sinp);
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// Position in EFEF
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const std::vector<double> pos_rx = {(v + h) * cosp * cosl, (v + h) * cosp * sinl, (v * (1.0 - e2) + h) * sinp};
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// Velovity in EFEF
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const double t = cosp * vu - sinp * vn;
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const std::vector<double> vel_rx = {cosl * t - sinl * ve, sinl * t + cosl * ve, sinp * vu + cosp * vn};
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std::array<double, 7> sat_pos_vel = {0};
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satellitePosVelComputation(rx_time_s, sat_pos_vel);
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const std::vector<double> pos_sat = {sat_pos_vel[0], sat_pos_vel[1], sat_pos_vel[2]};
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const std::vector<double> vel_sat = {sat_pos_vel[3], sat_pos_vel[4], sat_pos_vel[5]};
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std::vector<double> x_sr = pos_sat;
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std::transform(x_sr.begin(), x_sr.end(), pos_rx.begin(), x_sr.begin(), std::minus<double>()); // pos_sat - pos_rx
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const double norm_x_sr = std::sqrt(std::inner_product(x_sr.begin(), x_sr.end(), x_sr.begin(), 0.0)); // Euclidean norm
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std::vector<double> v_sr = vel_sat;
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std::transform(v_sr.begin(), v_sr.end(), vel_rx.begin(), v_sr.begin(), std::minus<double>()); // vel_sat - vel_rx
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const double radial_vel = std::inner_product(v_sr.begin(), v_sr.end(), x_sr.begin(), 0.0) / norm_x_sr;
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const double predicted_doppler_normalized = -(radial_vel / SPEED_OF_LIGHT_M_S);
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double predicted_doppler = 0.0;
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if (this->System == 'E') // Galileo
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{
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if (band == 1)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ1;
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}
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else if (band == 5)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ5;
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}
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else if (band == 6)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ6;
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}
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else if (band == 7)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ7;
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}
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else if (band == 8)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ8;
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}
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else
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{
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predicted_doppler = 0.0;
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}
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}
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else if (this->System == 'G') // GPS
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{
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if (band == 1)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ1;
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}
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else if (band == 2)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ2;
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}
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else if (band == 5)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ5;
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}
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else
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{
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predicted_doppler = 0.0;
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}
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}
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else if (this->System == 'B') // Beidou
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{
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if (band == 1)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ1_BDS;
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}
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else if (band == 2)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ2_BDS;
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}
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else if (band == 3)
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{
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predicted_doppler = predicted_doppler_normalized * FREQ3_BDS;
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}
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else
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{
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predicted_doppler = 0.0;
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}
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}
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else
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{
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predicted_doppler = 0.0;
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}
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return predicted_doppler;
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}
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void Gnss_Ephemeris::satellitePosition(double transmitTime)
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{
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std::array<double, 7> pos_vel_dtr = {0};
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satellitePosVelComputation(transmitTime, pos_vel_dtr);
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this->satpos_X = pos_vel_dtr[0];
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this->satpos_Y = pos_vel_dtr[1];
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this->satpos_Z = pos_vel_dtr[2];
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this->satvel_X = pos_vel_dtr[3];
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this->satvel_Y = pos_vel_dtr[4];
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this->satvel_Z = pos_vel_dtr[5];
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this->dtr = pos_vel_dtr[6];
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}
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void Gnss_Ephemeris::satellitePosVelComputation(double transmitTime, std::array<double, 7>& pos_vel_dtr) const
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{
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// Restore semi-major axis
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const double a = this->sqrtA * this->sqrtA;
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@ -128,45 +274,53 @@ void Gnss_Ephemeris::satellitePosition(double transmitTime)
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// --- Compute satellite coordinates in Earth-fixed coordinates
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const double xprime = r * cuk;
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const double yprime = r * suk;
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this->satpos_X = xprime * cok - yprime * cik * sok;
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this->satpos_Y = xprime * sok + yprime * cik * cok; // ********NOTE: in GALILEO ICD this expression is not correct because it has minus (- sin(u) * r * cos(i) * cos(Omega)) instead of plus
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this->satpos_Z = yprime * sik;
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pos_vel_dtr[0] = xprime * cok - yprime * cik * sok;
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pos_vel_dtr[1] = xprime * sok + yprime * cik * cok; // ********NOTE: in GALILEO ICD this expression is not correct because it has minus (- sin(u) * r * cos(i) * cos(Omega)) instead of plus
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pos_vel_dtr[2] = yprime * sik;
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// Satellite's velocity. Can be useful for Vector Tracking loops
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const double xpkdot = rkdot * cuk - yprime * ukdot;
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const double ypkdot = rkdot * suk + xprime * ukdot;
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const double tmp = ypkdot * cik - this->satpos_Z * ikdot;
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const double tmp = ypkdot * cik - pos_vel_dtr[2] * ikdot;
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this->satvel_X = -Omega_dot * this->satpos_Y + xpkdot * cok - tmp * sok;
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this->satvel_Y = Omega_dot * this->satpos_X + xpkdot * sok + tmp * cok;
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this->satvel_Z = yprime * cik * ikdot + ypkdot * sik;
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pos_vel_dtr[3] = -Omega_dot * pos_vel_dtr[1] + xpkdot * cok - tmp * sok;
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pos_vel_dtr[4] = Omega_dot * pos_vel_dtr[0] + xpkdot * sok + tmp * cok;
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pos_vel_dtr[5] = yprime * cik * ikdot + ypkdot * sik;
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// Time from ephemeris reference clock
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tk = check_t(transmitTime - this->toc);
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this->dtr = this->af0 + this->af1 * tk + this->af2 * tk * tk;
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pos_vel_dtr[6] = this->af0 + this->af1 * tk + this->af2 * tk * tk;
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if (this->System == 'E')
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{
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this->dtr -= 2.0 * sqrt(GALILEO_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
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pos_vel_dtr[6] -= 2.0 * sqrt(GALILEO_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
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}
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else if (this->System == 'B')
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{
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this->dtr -= 2.0 * sqrt(BEIDOU_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
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pos_vel_dtr[6] -= 2.0 * sqrt(BEIDOU_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
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}
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else
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{
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this->dtr -= 2.0 * sqrt(GPS_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
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pos_vel_dtr[6] -= 2.0 * sqrt(GPS_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
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}
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}
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double Gnss_Ephemeris::sv_clock_drift(double transmitTime)
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double Gnss_Ephemeris::check_t(double time) const
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{
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const double dt = check_t(transmitTime - this->toc);
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this->dtr = sv_clock_relativistic_term(transmitTime);
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this->satClkDrift = this->af0 + this->af1 * dt + this->af2 * (dt * dt) + this->dtr;
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return this->satClkDrift;
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const double half_week = 302400.0; // seconds
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double corrTime = time;
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if (time > half_week)
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{
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corrTime = time - 2.0 * half_week;
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}
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else if (time < -half_week)
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{
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corrTime = time + 2.0 * half_week;
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}
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return corrTime;
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}
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@ -184,7 +338,7 @@ double Gnss_Ephemeris::sv_clock_relativistic_term(double transmitTime) const
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{
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n0 = sqrt(GALILEO_GM / (a * a * a));
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}
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else if (this->System == 'E')
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else if (this->System == 'B')
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{
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n0 = sqrt(BEIDOU_GM / (a * a * a));
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}
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@ -235,19 +389,3 @@ double Gnss_Ephemeris::sv_clock_relativistic_term(double transmitTime) const
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}
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return dtr_;
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}
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double Gnss_Ephemeris::check_t(double time) const
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{
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const double half_week = 302400.0; // seconds
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double corrTime = time;
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if (time > half_week)
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{
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corrTime = time - 2.0 * half_week;
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}
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else if (time < -half_week)
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{
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corrTime = time + 2.0 * half_week;
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}
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return corrTime;
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}
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@ -19,6 +19,7 @@
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#ifndef GNSS_SDR_GNSS_EPHEMERIS_H
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#define GNSS_SDR_GNSS_EPHEMERIS_H
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#include <array>
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#include <cstdint>
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/*!
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@ -36,6 +37,20 @@ public:
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*/
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double sv_clock_drift(double transmitTime);
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/*!
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* \brief Computes prediction of the Doppler shift for a given time and receiver's position and velocity.
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* @param[in] rx_time_s Time of Week in seconds
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* @param[in] lat Receiver's latitude in degrees
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* @param[in] lon Receiver's longitude in degrees
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* @param[in] h Receiver's height in meters
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* @param[in] ve Receiver's velocity in the East direction [m/s]
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* @param[in] vn Receiver's velocity in the North direction [m/s]
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* @param[in] vu Receiver's velocity in the Up direction [m/s]
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* @param[in] band Signal band for which the Doppler will be computed
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* (1: L1 C/A, E1B, BI1; 2: L2C, BI2; 3: BI3; 5: L5/E5a; 6: E6B; 7: E5b; 8: E5a+E5b)
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*/
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double predicted_doppler(double rx_time_s, double lat, double lon, double h, double ve, double vn, double vu, int band) const;
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void satellitePosition(double transmitTime); //!< Computes the ECEF SV coordinates and ECEF velocity
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uint32_t PRN{}; //!< SV ID
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@ -83,6 +98,7 @@ protected:
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char System{}; //!< Character ID of the GNSS system. 'G': GPS. 'E': Galileo. 'B': BeiDou
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private:
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void satellitePosVelComputation(double transmitTime, std::array<double, 7>& pos_vel_dtr) const;
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double check_t(double time) const;
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double sv_clock_relativistic_term(double transmitTime) const;
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};
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