eive-obsw/mission/controller/acs/Igrf13Model.cpp

/*
 * Igrf13Model.cpp
 *
 *  Created on: 10 Mar 2022
 *      Author: Robin Marquardt
 */

#include "Igrf13Model.h"
#include "util/MathOperations.h"
#include <math.h>
#include <stdint.h>
#include <string.h>
//#include <time.h>
#include <fsfw/globalfunctions/constants.h>
#include <fsfw/globalfunctions/math/MatrixOperations.h>
#include <fsfw/globalfunctions/math/QuaternionOperations.h>
#include <fsfw/globalfunctions/math/VectorOperations.h>


Igrf13Model::Igrf13Model(){
}
Igrf13Model::~Igrf13Model(){
}

void Igrf13Model::magFieldComp(const double longitude, const double gcLatitude,
		const double altitude, timeval timeOfMagMeasurement, double* magFieldModelInertial) {

	double phi = longitude, theta = gcLatitude; //geocentric
	/* Here is the co-latitude needed*/
	theta -= 90*Math::PI/180;
	theta *= (-1);

	double rE = 6371200.0; // radius earth [m]
	/* Predefine recursive associated Legendre polynomials */
	double P11 = 1;
	double P10 = P11; //P10 = P(n-1,m-0)
	double dP11 = 0; //derivative
	double dP10 = dP11; //derivative

	double P2 = 0, dP2 = 0, P20 = 0, dP20 = 0, K = 0;

	for (int m = 0; m <= igrfOrder; m++) {
		for (int n = 1; n <= igrfOrder; n++) {
			if (m <= n) {
				/* Calculation of Legendre Polynoms (normalised) */
				if (n == m) {
					P2 = sin(theta) * P11;
					dP2 = sin(theta) * dP11 - cos(theta) * P11;
					P11 = P2;
					P10 = P11;
					P20 = 0;
					dP11 = dP2;
					dP10 = dP11;
					dP20 = 0;
				} else if (n == 1) {
					P2 = cos(theta) * P10;
					dP2 = cos(theta) * dP10 - sin(theta) * P10;
					P20 = P10;
					P10 = P2;
					dP20 = dP10;
					dP10 = dP2;
				} else {
					K = (pow((n - 1), 2) - pow(m, 2))
							/ ((2 * n - 1) * (2 * n - 3));
					P2 = cos(theta) * P10 - K * P20;
					dP2 = cos(theta) * dP10 - sin(theta) * P10 - K * dP20;
					P20 = P10;
					P10 = P2;
					dP20 = dP10;
					dP10 = dP2;
				}
			/* gradient of scalar potential towards radius */
			magFieldModel[0]+=pow(rE/(altitude+rE),(n+2))*(n+1)*
					((updatedG[m][n-1]*cos(m*phi) + updatedH[m][n-1]*sin(m*phi))*P2);
			/* gradient of scalar potential towards phi */
			magFieldModel[1]+=pow(rE/(altitude+rE),(n+2))*
					((updatedG[m][n-1]*cos(m*phi) + updatedH[m][n-1]*sin(m*phi))*dP2);
			/* gradient of scalar potential towards theta */
			magFieldModel[2]+=pow(rE/(altitude+rE),(n+2))*
					((-updatedG[m][n-1]*sin(m*phi) + updatedH[m][n-1]*cos(m*phi))*P2*m);
			}
		}
	}

	magFieldModel[1] *= -1;
	magFieldModel[2] *= (-1 / sin(theta));

	/* Next step: transform into inertial KOS (IJK)*/
	//Julean Centuries
	double JD2000Floor = 0;
	double JD2000 = MathOperations<double>::convertUnixToJD2000(timeOfMagMeasurement);
	JD2000Floor = floor(JD2000);
	double JC2000 = JD2000Floor / 36525;

	double gst = 100.4606184 + 36000.77005361 * JC2000 + 0.00038793 * pow(JC2000,2)
	- 0.000000026 * pow(JC2000,3); //greenwich sidereal time
	gst *= PI/180; //convert to radians
	double sec = (JD2000 - JD2000Floor) * 86400; // Seconds on this day (Universal time) // FROM GPS ?
	double omega0 = 0.00007292115; // mean angular velocity earth [rad/s]
	gst +=omega0 * sec;

	double lst = gst + longitude; //local sidereal time [rad]



    magFieldModelInertial[0] = magFieldModel[0] * cos(theta) + magFieldModel[1] * sin(theta)*cos(lst) - magFieldModel[1] * sin(lst);
    magFieldModelInertial[1] = magFieldModel[0] * cos(theta) + magFieldModel[1] * sin(theta)*sin(lst) + magFieldModel[1] * cos(lst);
    magFieldModelInertial[2] = magFieldModel[0] * sin(theta) + magFieldModel[1] * cos(lst);

    double normVecMagFieldInert[3] = {0,0,0};
	VectorOperations<double>::normalize(magFieldModelInertial, normVecMagFieldInert, 3);
}

void Igrf13Model::updateCoeffGH(timeval timeOfMagMeasurement){

	double JD2000Igrf = (2458850.0-2451545); //Begin of IGRF-13 (2020-01-01,00:00:00) in JD2000
	double JD2000 = MathOperations<double>::convertUnixToJD2000(timeOfMagMeasurement);
	double days = ceil(JD2000-JD2000Igrf);
	for(int i = 0;i <= igrfOrder; i++){
		for(int j = 0;j <= (igrfOrder-1); j++){
			updatedG[i][j] = coeffG[i][j] + svG[i][j] * (days/365);
			updatedH[i][j] = coeffH[i][j] + svH[i][j] * (days/365);
		}
	}
}