mirror of https://github.com/gnss-sdr/gnss-sdr
276 lines
8.6 KiB
C++
276 lines
8.6 KiB
C++
/*!
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* \file gnss_almanac.cc
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* \brief Base class for GNSS almanac storage
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* \author Carles Fernandez, 2022. cfernandez(at)cttc.es
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*
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* -----------------------------------------------------------------------------
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*
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* GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
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* This file is part of GNSS-SDR.
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*
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* Copyright (C) 2010-2022 (see AUTHORS file for a list of contributors)
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* SPDX-License-Identifier: GPL-3.0-or-later
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*
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* -----------------------------------------------------------------------------
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*/
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#include "gnss_almanac.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_Almanac::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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double Gnss_Almanac::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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// Velocity 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_Almanac::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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// Computed mean motion
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double n;
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if (this->System == 'E')
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{
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n = sqrt(GALILEO_GM / (a * a * a));
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}
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else if (this->System == 'B')
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{
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n = sqrt(BEIDOU_GM / (a * a * a));
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}
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else
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{
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n = sqrt(GPS_GM / (a * a * a));
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}
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// Time from ephemeris reference epoch
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const double tk = check_t(transmitTime - static_cast<double>(this->toa));
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// Mean anomaly
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const double M = this->M_0 * GNSS_PI + n * tk;
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// Initial guess of eccentric anomaly
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double E = M;
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double E_old;
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double dE;
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// --- Iteratively compute eccentric anomaly -------------------------------
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for (int32_t ii = 1; ii < 20; ii++)
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{
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E_old = E;
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E = M + this->ecc * sin(E);
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dE = fmod(E - E_old, 2.0 * GNSS_PI);
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if (fabs(dE) < 1e-12)
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{
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// Necessary precision is reached, exit from the loop
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break;
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}
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}
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const double sek = sin(E);
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const double cek = cos(E);
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const double OneMinusecosE = 1.0 - this->ecc * cek;
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const double sq1e2 = sqrt(1.0 - this->ecc * this->ecc);
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const double ekdot = n / OneMinusecosE;
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// Compute the true anomaly
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const double tmp_Y = sq1e2 * sek;
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const double tmp_X = cek - this->ecc;
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const double nu = atan2(tmp_Y, tmp_X);
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// Compute angle phi (argument of Latitude)
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const double phi = nu + this->omega * GNSS_PI;
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const double pkdot = sq1e2 * ekdot / OneMinusecosE;
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// Correct argument of latitude
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const double suk = sin(phi);
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const double cuk = cos(phi);
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// Correct radius
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const double r = a * OneMinusecosE;
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const double rkdot = a * this->ecc * sek * ekdot;
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// Correct inclination
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double i;
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if (this->System == 'E')
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{
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i = ((56.0 / 180.0) + this->delta_i) * GNSS_PI;
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}
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else
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{
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i = (0.3 + this->delta_i) * GNSS_PI;
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}
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const double sik = sin(i);
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const double cik = cos(i);
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// Compute the angle between the ascending node and the Greenwich meridian
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double Omega;
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double Omega_dot;
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if (this->System == 'B')
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{
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Omega_dot = this->OMEGAdot * GNSS_PI - BEIDOU_OMEGA_EARTH_DOT;
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Omega = this->OMEGA_0 * GNSS_PI + Omega_dot * tk - BEIDOU_OMEGA_EARTH_DOT * static_cast<double>(this->toa);
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}
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else
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{
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Omega_dot = this->OMEGAdot * GNSS_PI - GNSS_OMEGA_EARTH_DOT;
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Omega = this->OMEGA_0 * GNSS_PI + Omega_dot * tk - GNSS_OMEGA_EARTH_DOT * static_cast<double>(this->toa);
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}
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const double sok = sin(Omega);
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const double cok = cos(Omega);
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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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pos_vel_dtr[0] = xprime * cok - yprime * cik * sok;
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pos_vel_dtr[1] = xprime * sok + yprime * cik * cok;
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pos_vel_dtr[2] = yprime * sik;
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// Satellite's velocity
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const double xpkdot = rkdot * cuk - yprime * pkdot;
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const double ypkdot = rkdot * suk + xprime * pkdot;
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const double tmp = ypkdot * cik;
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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] = ypkdot * sik;
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pos_vel_dtr[6] = 0;
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}
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