HolmesFeatherstoneAttractionModel.java
/* Copyright 2002-2016 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
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package org.orekit.forces.gravity;
import java.io.Serializable;
import org.hipparchus.analysis.differentiation.DerivativeStructure;
import org.hipparchus.geometry.euclidean.threed.FieldRotation;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.SphericalCoordinates;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.linear.Array2DRowRealMatrix;
import org.hipparchus.linear.RealMatrix;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.forces.AbstractForceModel;
import org.orekit.forces.gravity.potential.NormalizedSphericalHarmonicsProvider;
import org.orekit.forces.gravity.potential.NormalizedSphericalHarmonicsProvider.NormalizedSphericalHarmonics;
import org.orekit.forces.gravity.potential.TideSystem;
import org.orekit.forces.gravity.potential.TideSystemProvider;
import org.orekit.frames.Frame;
import org.orekit.frames.Transform;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.EventDetector;
import org.orekit.propagation.numerical.TimeDerivativesEquations;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.ParameterObserver;
/** This class represents the gravitational field of a celestial body.
* <p>
* The algorithm implemented in this class has been designed by S. A. Holmes
* and W. E. Featherstone from Department of Spatial Sciences, Curtin University
* of Technology, Perth, Australia. It is described in their 2002 paper: <a
* href="http://cct.gfy.ku.dk/publ_others/ccta1870.pdf">A unified approach to
* the Clenshaw summation and the recursive computation of very high degree and
* order normalised associated Legendre functions</a> (Journal of Geodesy (2002)
* 76: 279–299).
* </p>
* <p>
* This model directly uses normalized coefficients and stable recursion algorithms
* so it is more suited to high degree gravity fields than the classical {@link
* CunninghamAttractionModel Cunningham} or {@link DrozinerAttractionModel Droziner}
* models which use un-normalized coefficients.
* </p>
* <p>
* Among the different algorithms presented in Holmes and Featherstone paper, this
* class implements the <em>modified forward row method</em>. All recursion coefficients
* are precomputed and stored for greater performance. This caching was suggested in the
* paper but not used due to the large memory requirements. Since 2002, even low end
* computers and mobile devices do have sufficient memory so this caching has become
* feasible nowadays.
* <p>
* @author Luc Maisonobe
* @since 6.0
*/
public class HolmesFeatherstoneAttractionModel extends AbstractForceModel implements TideSystemProvider {
/** Exponent scaling to avoid floating point overflow.
* <p>The paper uses 10^280, we prefer a power of two to preserve accuracy thanks to
* {@link FastMath#scalb(double, int)}, so we use 2^930 which has the same order of magnitude.
*/
private static final int SCALING = 930;
/** Central attraction scaling factor.
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private static final double MU_SCALE = FastMath.scalb(1.0, 32);
/** Drivers for force model parameters. */
private final ParameterDriver[] parametersDrivers;
/** Provider for the spherical harmonics. */
private final NormalizedSphericalHarmonicsProvider provider;
/** Central attraction coefficient. */
private double mu;
/** Rotating body. */
private final Frame bodyFrame;
/** Recursion coefficients g<sub>n,m</sub>/√j. */
private final double[] gnmOj;
/** Recursion coefficients h<sub>n,m</sub>/√j. */
private final double[] hnmOj;
/** Recursion coefficients e<sub>n,m</sub>. */
private final double[] enm;
/** Scaled sectorial Pbar<sub>m,m</sub>/u<sup>m</sup> × 2<sup>-SCALING</sup>. */
private final double[] sectorial;
/** Creates a new instance.
* @param centralBodyFrame rotating body frame
* @param provider provider for spherical harmonics
* @since 6.0
*/
public HolmesFeatherstoneAttractionModel(final Frame centralBodyFrame,
final NormalizedSphericalHarmonicsProvider provider) {
this.parametersDrivers = new ParameterDriver[1];
try {
parametersDrivers[0] = new ParameterDriver(NewtonianAttraction.CENTRAL_ATTRACTION_COEFFICIENT,
provider.getMu(), MU_SCALE, 0.0, Double.POSITIVE_INFINITY);
parametersDrivers[0].addObserver(new ParameterObserver() {
/** {@inheritDoc} */
@Override
public void valueChanged(final double previousValue, final ParameterDriver driver) {
HolmesFeatherstoneAttractionModel.this.mu = driver.getValue();
}
});
} catch (OrekitException oe) {
// this should never occur as valueChanged above never throws an exception
throw new OrekitInternalError(oe);
};
this.provider = provider;
this.mu = provider.getMu();
this.bodyFrame = centralBodyFrame;
// the pre-computed arrays hold coefficients from triangular arrays in a single
// storing neither diagonal elements (n = m) nor the non-diagonal element n=1, m=0
final int degree = provider.getMaxDegree();
final int size = FastMath.max(0, degree * (degree + 1) / 2 - 1);
gnmOj = new double[size];
hnmOj = new double[size];
enm = new double[size];
// pre-compute the recursion coefficients corresponding to equations 19 and 22
// from Holmes and Featherstone paper
// for cache efficiency, elements are stored in the same order they will be used
// later on, i.e. from rightmost column to leftmost column
int index = 0;
for (int m = degree; m >= 0; --m) {
final int j = (m == 0) ? 2 : 1;
for (int n = FastMath.max(2, m + 1); n <= degree; ++n) {
final double f = (n - m) * (n + m + 1);
gnmOj[index] = 2 * (m + 1) / FastMath.sqrt(j * f);
hnmOj[index] = FastMath.sqrt((n + m + 2) * (n - m - 1) / (j * f));
enm[index] = FastMath.sqrt(f / j);
++index;
}
}
// scaled sectorial terms corresponding to equation 28 in Holmes and Featherstone paper
sectorial = new double[degree + 1];
sectorial[0] = FastMath.scalb(1.0, -SCALING);
sectorial[1] = FastMath.sqrt(3) * sectorial[0];
for (int m = 2; m < sectorial.length; ++m) {
sectorial[m] = FastMath.sqrt((2 * m + 1) / (2.0 * m)) * sectorial[m - 1];
}
}
/** {@inheritDoc} */
public TideSystem getTideSystem() {
return provider.getTideSystem();
}
/** Compute the value of the gravity field.
* @param date current date
* @param position position at which gravity field is desired in body frame
* @return value of the gravity field (central and non-central parts summed together)
* @exception OrekitException if position cannot be converted to central body frame
*/
public double value(final AbsoluteDate date, final Vector3D position)
throws OrekitException {
return mu / position.getNorm() + nonCentralPart(date, position);
}
/** Compute the non-central part of the gravity field.
* @param date current date
* @param position position at which gravity field is desired in body frame
* @return value of the non-central part of the gravity field
* @exception OrekitException if position cannot be converted to central body frame
*/
public double nonCentralPart(final AbsoluteDate date, final Vector3D position)
throws OrekitException {
final int degree = provider.getMaxDegree();
final int order = provider.getMaxOrder();
final NormalizedSphericalHarmonics harmonics = provider.onDate(date);
// allocate the columns for recursion
double[] pnm0Plus2 = new double[degree + 1];
double[] pnm0Plus1 = new double[degree + 1];
double[] pnm0 = new double[degree + 1];
// compute polar coordinates
final double x = position.getX();
final double y = position.getY();
final double z = position.getZ();
final double x2 = x * x;
final double y2 = y * y;
final double z2 = z * z;
final double r2 = x2 + y2 + z2;
final double r = FastMath.sqrt (r2);
final double rho = FastMath.sqrt(x2 + y2);
final double t = z / r; // cos(theta), where theta is the polar angle
final double u = rho / r; // sin(theta), where theta is the polar angle
final double tOu = z / rho;
// compute distance powers
final double[] aOrN = createDistancePowersArray(provider.getAe() / r);
// compute longitude cosines/sines
final double[][] cosSinLambda = createCosSinArrays(position.getX() / rho, position.getY() / rho);
// outer summation over order
int index = 0;
double value = 0;
for (int m = degree; m >= 0; --m) {
// compute tesseral terms without derivatives
index = computeTesseral(m, degree, index, t, u, tOu,
pnm0Plus2, pnm0Plus1, null, pnm0, null, null);
if (m <= order) {
// compute contribution of current order to field (equation 5 of the paper)
// inner summation over degree, for fixed order
double sumDegreeS = 0;
double sumDegreeC = 0;
for (int n = FastMath.max(2, m); n <= degree; ++n) {
sumDegreeS += pnm0[n] * aOrN[n] * harmonics.getNormalizedSnm(n, m);
sumDegreeC += pnm0[n] * aOrN[n] * harmonics.getNormalizedCnm(n, m);
}
// contribution to outer summation over order
value = value * u + cosSinLambda[1][m] * sumDegreeS + cosSinLambda[0][m] * sumDegreeC;
}
// rotate the recursion arrays
final double[] tmp = pnm0Plus2;
pnm0Plus2 = pnm0Plus1;
pnm0Plus1 = pnm0;
pnm0 = tmp;
}
// scale back
value = FastMath.scalb(value, SCALING);
// apply the global mu/r factor
return mu * value / r;
}
/** Compute the gradient of the non-central part of the gravity field.
* @param date current date
* @param position position at which gravity field is desired in body frame
* @return gradient of the non-central part of the gravity field
* @exception OrekitException if position cannot be converted to central body frame
*/
public double[] gradient(final AbsoluteDate date, final Vector3D position)
throws OrekitException {
final int degree = provider.getMaxDegree();
final int order = provider.getMaxOrder();
final NormalizedSphericalHarmonics harmonics = provider.onDate(date);
// allocate the columns for recursion
double[] pnm0Plus2 = new double[degree + 1];
double[] pnm0Plus1 = new double[degree + 1];
double[] pnm0 = new double[degree + 1];
final double[] pnm1 = new double[degree + 1];
// compute polar coordinates
final double x = position.getX();
final double y = position.getY();
final double z = position.getZ();
final double x2 = x * x;
final double y2 = y * y;
final double z2 = z * z;
final double r2 = x2 + y2 + z2;
final double r = FastMath.sqrt (r2);
final double rho2 = x2 + y2;
final double rho = FastMath.sqrt(rho2);
final double t = z / r; // cos(theta), where theta is the polar angle
final double u = rho / r; // sin(theta), where theta is the polar angle
final double tOu = z / rho;
// compute distance powers
final double[] aOrN = createDistancePowersArray(provider.getAe() / r);
// compute longitude cosines/sines
final double[][] cosSinLambda = createCosSinArrays(position.getX() / rho, position.getY() / rho);
// outer summation over order
int index = 0;
double value = 0;
final double[] gradient = new double[3];
for (int m = degree; m >= 0; --m) {
// compute tesseral terms with derivatives
index = computeTesseral(m, degree, index, t, u, tOu,
pnm0Plus2, pnm0Plus1, null, pnm0, pnm1, null);
if (m <= order) {
// compute contribution of current order to field (equation 5 of the paper)
// inner summation over degree, for fixed order
double sumDegreeS = 0;
double sumDegreeC = 0;
double dSumDegreeSdR = 0;
double dSumDegreeCdR = 0;
double dSumDegreeSdTheta = 0;
double dSumDegreeCdTheta = 0;
for (int n = FastMath.max(2, m); n <= degree; ++n) {
final double qSnm = aOrN[n] * harmonics.getNormalizedSnm(n, m);
final double qCnm = aOrN[n] * harmonics.getNormalizedCnm(n, m);
final double nOr = n / r;
final double s0 = pnm0[n] * qSnm;
final double c0 = pnm0[n] * qCnm;
final double s1 = pnm1[n] * qSnm;
final double c1 = pnm1[n] * qCnm;
sumDegreeS += s0;
sumDegreeC += c0;
dSumDegreeSdR -= nOr * s0;
dSumDegreeCdR -= nOr * c0;
dSumDegreeSdTheta += s1;
dSumDegreeCdTheta += c1;
}
// contribution to outer summation over order
// beware that we need to order gradient using the mathematical conventions
// compliant with the SphericalCoordinates class, so our lambda is its theta
// (and hence at index 1) and our theta is its phi (and hence at index 2)
final double sML = cosSinLambda[1][m];
final double cML = cosSinLambda[0][m];
value = value * u + sML * sumDegreeS + cML * sumDegreeC;
gradient[0] = gradient[0] * u + sML * dSumDegreeSdR + cML * dSumDegreeCdR;
gradient[1] = gradient[1] * u + m * (cML * sumDegreeS - sML * sumDegreeC);
gradient[2] = gradient[2] * u + sML * dSumDegreeSdTheta + cML * dSumDegreeCdTheta;
}
// rotate the recursion arrays
final double[] tmp = pnm0Plus2;
pnm0Plus2 = pnm0Plus1;
pnm0Plus1 = pnm0;
pnm0 = tmp;
}
// scale back
value = FastMath.scalb(value, SCALING);
gradient[0] = FastMath.scalb(gradient[0], SCALING);
gradient[1] = FastMath.scalb(gradient[1], SCALING);
gradient[2] = FastMath.scalb(gradient[2], SCALING);
// apply the global mu/r factor
final double muOr = mu / r;
value *= muOr;
gradient[0] = muOr * gradient[0] - value / r;
gradient[1] *= muOr;
gradient[2] *= muOr;
// convert gradient from spherical to Cartesian
return new SphericalCoordinates(position).toCartesianGradient(gradient);
}
/** Compute both the gradient and the hessian of the non-central part of the gravity field.
* @param date current date
* @param position position at which gravity field is desired in body frame
* @return gradient and hessian of the non-central part of the gravity field
* @exception OrekitException if position cannot be converted to central body frame
*/
public GradientHessian gradientHessian(final AbsoluteDate date, final Vector3D position)
throws OrekitException {
final int degree = provider.getMaxDegree();
final int order = provider.getMaxOrder();
final NormalizedSphericalHarmonics harmonics = provider.onDate(date);
// allocate the columns for recursion
double[] pnm0Plus2 = new double[degree + 1];
double[] pnm0Plus1 = new double[degree + 1];
double[] pnm0 = new double[degree + 1];
double[] pnm1Plus1 = new double[degree + 1];
double[] pnm1 = new double[degree + 1];
final double[] pnm2 = new double[degree + 1];
// compute polar coordinates
final double x = position.getX();
final double y = position.getY();
final double z = position.getZ();
final double x2 = x * x;
final double y2 = y * y;
final double z2 = z * z;
final double r2 = x2 + y2 + z2;
final double r = FastMath.sqrt (r2);
final double rho2 = x2 + y2;
final double rho = FastMath.sqrt(rho2);
final double t = z / r; // cos(theta), where theta is the polar angle
final double u = rho / r; // sin(theta), where theta is the polar angle
final double tOu = z / rho;
// compute distance powers
final double[] aOrN = createDistancePowersArray(provider.getAe() / r);
// compute longitude cosines/sines
final double[][] cosSinLambda = createCosSinArrays(position.getX() / rho, position.getY() / rho);
// outer summation over order
int index = 0;
double value = 0;
final double[] gradient = new double[3];
final double[][] hessian = new double[3][3];
for (int m = degree; m >= 0; --m) {
// compute tesseral terms
index = computeTesseral(m, degree, index, t, u, tOu,
pnm0Plus2, pnm0Plus1, pnm1Plus1, pnm0, pnm1, pnm2);
if (m <= order) {
// compute contribution of current order to field (equation 5 of the paper)
// inner summation over degree, for fixed order
double sumDegreeS = 0;
double sumDegreeC = 0;
double dSumDegreeSdR = 0;
double dSumDegreeCdR = 0;
double dSumDegreeSdTheta = 0;
double dSumDegreeCdTheta = 0;
double d2SumDegreeSdRdR = 0;
double d2SumDegreeSdRdTheta = 0;
double d2SumDegreeSdThetadTheta = 0;
double d2SumDegreeCdRdR = 0;
double d2SumDegreeCdRdTheta = 0;
double d2SumDegreeCdThetadTheta = 0;
for (int n = FastMath.max(2, m); n <= degree; ++n) {
final double qSnm = aOrN[n] * harmonics.getNormalizedSnm(n, m);
final double qCnm = aOrN[n] * harmonics.getNormalizedCnm(n, m);
final double nOr = n / r;
final double nnP1Or2 = nOr * (n + 1) / r;
final double s0 = pnm0[n] * qSnm;
final double c0 = pnm0[n] * qCnm;
final double s1 = pnm1[n] * qSnm;
final double c1 = pnm1[n] * qCnm;
final double s2 = pnm2[n] * qSnm;
final double c2 = pnm2[n] * qCnm;
sumDegreeS += s0;
sumDegreeC += c0;
dSumDegreeSdR -= nOr * s0;
dSumDegreeCdR -= nOr * c0;
dSumDegreeSdTheta += s1;
dSumDegreeCdTheta += c1;
d2SumDegreeSdRdR += nnP1Or2 * s0;
d2SumDegreeSdRdTheta -= nOr * s1;
d2SumDegreeSdThetadTheta += s2;
d2SumDegreeCdRdR += nnP1Or2 * c0;
d2SumDegreeCdRdTheta -= nOr * c1;
d2SumDegreeCdThetadTheta += c2;
}
// contribution to outer summation over order
final double sML = cosSinLambda[1][m];
final double cML = cosSinLambda[0][m];
value = value * u + sML * sumDegreeS + cML * sumDegreeC;
gradient[0] = gradient[0] * u + sML * dSumDegreeSdR + cML * dSumDegreeCdR;
gradient[1] = gradient[1] * u + m * (cML * sumDegreeS - sML * sumDegreeC);
gradient[2] = gradient[2] * u + sML * dSumDegreeSdTheta + cML * dSumDegreeCdTheta;
hessian[0][0] = hessian[0][0] * u + sML * d2SumDegreeSdRdR + cML * d2SumDegreeCdRdR;
hessian[1][0] = hessian[1][0] * u + m * (cML * dSumDegreeSdR - sML * dSumDegreeCdR);
hessian[2][0] = hessian[2][0] * u + sML * d2SumDegreeSdRdTheta + cML * d2SumDegreeCdRdTheta;
hessian[1][1] = hessian[1][1] * u - m * m * (sML * sumDegreeS + cML * sumDegreeC);
hessian[2][1] = hessian[2][1] * u + m * (cML * dSumDegreeSdTheta - sML * dSumDegreeCdTheta);
hessian[2][2] = hessian[2][2] * u + sML * d2SumDegreeSdThetadTheta + cML * d2SumDegreeCdThetadTheta;
}
// rotate the recursion arrays
final double[] tmp0 = pnm0Plus2;
pnm0Plus2 = pnm0Plus1;
pnm0Plus1 = pnm0;
pnm0 = tmp0;
final double[] tmp1 = pnm1Plus1;
pnm1Plus1 = pnm1;
pnm1 = tmp1;
}
// scale back
value = FastMath.scalb(value, SCALING);
for (int i = 0; i < 3; ++i) {
gradient[i] = FastMath.scalb(gradient[i], SCALING);
for (int j = 0; j <= i; ++j) {
hessian[i][j] = FastMath.scalb(hessian[i][j], SCALING);
}
}
// apply the global mu/r factor
final double muOr = mu / r;
value *= muOr;
gradient[0] = muOr * gradient[0] - value / r;
gradient[1] *= muOr;
gradient[2] *= muOr;
hessian[0][0] = muOr * hessian[0][0] - 2 * gradient[0] / r;
hessian[1][0] = muOr * hessian[1][0] - gradient[1] / r;
hessian[2][0] = muOr * hessian[2][0] - gradient[2] / r;
hessian[1][1] *= muOr;
hessian[2][1] *= muOr;
hessian[2][2] *= muOr;
// convert gradient and Hessian from spherical to Cartesian
final SphericalCoordinates sc = new SphericalCoordinates(position);
return new GradientHessian(sc.toCartesianGradient(gradient),
sc.toCartesianHessian(hessian, gradient));
}
/** Container for gradient and Hessian. */
public static class GradientHessian implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20130219L;
/** Gradient. */
private final double[] gradient;
/** Hessian. */
private final double[][] hessian;
/** Simple constructor.
* <p>
* A reference to the arrays is stored, they are <strong>not</strong> cloned.
* </p>
* @param gradient gradient
* @param hessian hessian
*/
public GradientHessian(final double[] gradient, final double[][] hessian) {
this.gradient = gradient;
this.hessian = hessian;
}
/** Get a reference to the gradient.
* @return gradient (a reference to the internal array is returned)
*/
public double[] getGradient() {
return gradient;
}
/** Get a reference to the Hessian.
* @return Hessian (a reference to the internal array is returned)
*/
public double[][] getHessian() {
return hessian;
}
}
/** Compute a/r powers array.
* @param aOr a/r
* @return array containing (a/r)<sup>n</sup>
*/
private double[] createDistancePowersArray(final double aOr) {
// initialize array
final double[] aOrN = new double[provider.getMaxDegree() + 1];
aOrN[0] = 1;
aOrN[1] = aOr;
// fill up array
for (int n = 2; n < aOrN.length; ++n) {
final int p = n / 2;
final int q = n - p;
aOrN[n] = aOrN[p] * aOrN[q];
}
return aOrN;
}
/** Compute longitude cosines and sines.
* @param cosLambda cos(λ)
* @param sinLambda sin(λ)
* @return array containing cos(m × λ) in row 0
* and sin(m × λ) in row 1
*/
private double[][] createCosSinArrays(final double cosLambda, final double sinLambda) {
// initialize arrays
final double[][] cosSin = new double[2][provider.getMaxOrder() + 1];
cosSin[0][0] = 1;
cosSin[1][0] = 0;
if (provider.getMaxOrder() > 0) {
cosSin[0][1] = cosLambda;
cosSin[1][1] = sinLambda;
// fill up array
for (int m = 2; m < cosSin[0].length; ++m) {
// m * lambda is split as p * lambda + q * lambda, trying to avoid
// p or q being much larger than the other. This reduces the number of
// intermediate results reused to compute each value, and hence should limit
// as much as possible roundoff error accumulation
// (this does not change the number of floating point operations)
final int p = m / 2;
final int q = m - p;
cosSin[0][m] = cosSin[0][p] * cosSin[0][q] - cosSin[1][p] * cosSin[1][q];
cosSin[1][m] = cosSin[1][p] * cosSin[0][q] + cosSin[0][p] * cosSin[1][q];
}
}
return cosSin;
}
/** Compute one order of tesseral terms.
* <p>
* This corresponds to equations 27 and 30 of the paper.
* </p>
* @param m current order
* @param degree max degree
* @param index index in the flattened array
* @param t cos(θ), where θ is the polar angle
* @param u sin(θ), where θ is the polar angle
* @param tOu t/u
* @param pnm0Plus2 array containing scaled P<sub>n,m+2</sub>/u<sup>m+2</sup>
* @param pnm0Plus1 array containing scaled P<sub>n,m+1</sub>/u<sup>m+1</sup>
* @param pnm1Plus1 array containing scaled dP<sub>n,m+1</sub>/u<sup>m+1</sup>
* (may be null if second derivatives are not needed)
* @param pnm0 array to fill with scaled P<sub>n,m</sub>/u<sup>m</sup>
* @param pnm1 array to fill with scaled dP<sub>n,m</sub>/u<sup>m</sup>
* (may be null if first derivatives are not needed)
* @param pnm2 array to fill with scaled d²P<sub>n,m</sub>/u<sup>m</sup>
* (may be null if second derivatives are not needed)
* @return new value for index
*/
private int computeTesseral(final int m, final int degree, final int index,
final double t, final double u, final double tOu,
final double[] pnm0Plus2, final double[] pnm0Plus1, final double[] pnm1Plus1,
final double[] pnm0, final double[] pnm1, final double[] pnm2) {
final double u2 = u * u;
// initialize recursion from sectorial terms
int n = FastMath.max(2, m);
if (n == m) {
pnm0[n] = sectorial[n];
++n;
}
// compute tesseral values
int localIndex = index;
while (n <= degree) {
// value (equation 27 of the paper)
pnm0[n] = gnmOj[localIndex] * t * pnm0Plus1[n] - hnmOj[localIndex] * u2 * pnm0Plus2[n];
++localIndex;
++n;
}
if (pnm1 != null) {
// initialize recursion from sectorial terms
n = FastMath.max(2, m);
if (n == m) {
pnm1[n] = m * tOu * pnm0[n];
++n;
}
// compute tesseral values and derivatives with respect to polar angle
localIndex = index;
while (n <= degree) {
// first derivative (equation 30 of the paper)
pnm1[n] = m * tOu * pnm0[n] - enm[localIndex] * u * pnm0Plus1[n];
++localIndex;
++n;
}
if (pnm2 != null) {
// initialize recursion from sectorial terms
n = FastMath.max(2, m);
if (n == m) {
pnm2[n] = m * (tOu * pnm1[n] - pnm0[n] / u2);
++n;
}
// compute tesseral values and derivatives with respect to polar angle
localIndex = index;
while (n <= degree) {
// second derivative (differential of equation 30 with respect to theta)
pnm2[n] = m * (tOu * pnm1[n] - pnm0[n] / u2) - enm[localIndex] * u * pnm1Plus1[n];
++localIndex;
++n;
}
}
}
return localIndex;
}
/** {@inheritDoc} */
public void addContribution(final SpacecraftState s, final TimeDerivativesEquations adder)
throws OrekitException {
// get the position in body frame
final AbsoluteDate date = s.getDate();
final Transform fromBodyFrame = bodyFrame.getTransformTo(s.getFrame(), date);
final Transform toBodyFrame = fromBodyFrame.getInverse();
final Vector3D position = toBodyFrame.transformPosition(s.getPVCoordinates().getPosition());
// gradient of the non-central part of the gravity field
final Vector3D gInertial = fromBodyFrame.transformVector(new Vector3D(gradient(date, position)));
adder.addXYZAcceleration(gInertial.getX(), gInertial.getY(), gInertial.getZ());
}
/** {@inheritDoc} */
public EventDetector[] getEventsDetectors() {
return new EventDetector[0];
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> accelerationDerivatives(final AbsoluteDate date, final Frame frame,
final FieldVector3D<DerivativeStructure> position, final FieldVector3D<DerivativeStructure> velocity,
final FieldRotation<DerivativeStructure> rotation, final DerivativeStructure mass)
throws OrekitException {
// get the position in body frame
final Transform fromBodyFrame = bodyFrame.getTransformTo(frame, date);
final Transform toBodyFrame = fromBodyFrame.getInverse();
final Vector3D positionBody = toBodyFrame.transformPosition(position.toVector3D());
// compute gradient and Hessian
final GradientHessian gh = gradientHessian(date, positionBody);
// gradient of the non-central part of the gravity field
final double[] gInertial = fromBodyFrame.transformVector(new Vector3D(gh.getGradient())).toArray();
// Hessian of the non-central part of the gravity field
final RealMatrix hBody = new Array2DRowRealMatrix(gh.getHessian(), false);
final RealMatrix rot = new Array2DRowRealMatrix(toBodyFrame.getRotation().getMatrix());
final RealMatrix hInertial = rot.transpose().multiply(hBody).multiply(rot);
// distribute all partial derivatives in a compact acceleration vector
final int parameters = mass.getFreeParameters();
final int order = mass.getOrder();
final double[] derivatives = new double[1 + parameters];
final DerivativeStructure[] accDer = new DerivativeStructure[3];
for (int i = 0; i < 3; ++i) {
// first element is value of acceleration (i.e. gradient of field)
derivatives[0] = gInertial[i];
// next three elements are one row of the Jacobian of acceleration (i.e. Hessian of field)
derivatives[1] = hInertial.getEntry(i, 0);
derivatives[2] = hInertial.getEntry(i, 1);
derivatives[3] = hInertial.getEntry(i, 2);
// next elements (three or four depending on mass being used or not) are left as 0
accDer[i] = new DerivativeStructure(parameters, order, derivatives);
}
return new FieldVector3D<DerivativeStructure>(accDer);
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> accelerationDerivatives(final SpacecraftState s, final String paramName)
throws OrekitException, IllegalArgumentException {
complainIfNotSupported(paramName);
// get the position in body frame
final AbsoluteDate date = s.getDate();
final Transform fromBodyFrame = bodyFrame.getTransformTo(s.getFrame(), date);
final Transform toBodyFrame = fromBodyFrame.getInverse();
final Vector3D position = toBodyFrame.transformPosition(s.getPVCoordinates().getPosition());
// gradient of the non-central part of the gravity field
final Vector3D gInertial = fromBodyFrame.transformVector(new Vector3D(gradient(date, position)));
return new FieldVector3D<DerivativeStructure>(new DerivativeStructure(1, 1, gInertial.getX(), gInertial.getX() / mu),
new DerivativeStructure(1, 1, gInertial.getY(), gInertial.getY() / mu),
new DerivativeStructure(1, 1, gInertial.getZ(), gInertial.getZ() / mu));
}
/** {@inheritDoc} */
public ParameterDriver[] getParametersDrivers() {
return parametersDrivers.clone();
}
}