Commit a72c8c58 authored by Luc Maisonobe's avatar Luc Maisonobe

Fixed Newcomb operators generation for high degree gravity fields.

Fixes issue #237
parent 5286ebe3
......@@ -23,7 +23,6 @@ import java.util.SortedMap;
import java.util.TreeMap;
import org.apache.commons.math3.analysis.polynomials.PolynomialFunction;
import org.apache.commons.math3.analysis.polynomials.PolynomialsUtils;
import org.apache.commons.math3.util.FastMath;
/** Implementation of the Modified Newcomb Operators.
......@@ -312,8 +311,7 @@ public class NewcombOperators {
}
}
/** Shift a list of {@link PolynomialFunction}, from the
* {@link PolynomialsUtils#shift(double[], double)} method.
/** Shift a list of {@link PolynomialFunction}.
*
* @param polynomialList list of {@link PolynomialFunction}
* @param shift shift value
......@@ -323,11 +321,70 @@ public class NewcombOperators {
final int shift) {
final List<PolynomialFunction> shiftedList = new ArrayList<PolynomialFunction>();
for (PolynomialFunction function : polynomialList) {
shiftedList.add(new PolynomialFunction(PolynomialsUtils.shift(function.getCoefficients(), shift)));
shiftedList.add(new PolynomialFunction(shift(function.getCoefficients(), shift)));
}
return shiftedList;
}
/**
* Compute the coefficients of the polynomial \(P_s(x)\)
* whose values at point {@code x} will be the same as the those from the
* original polynomial \(P(x)\) when computed at {@code x + shift}.
* <p>
* More precisely, let \(\Delta = \) {@code shift} and let
* \(P_s(x) = P(x + \Delta)\). The returned array
* consists of the coefficients of \(P_s\). So if \(a_0, ..., a_{n-1}\)
* are the coefficients of \(P\), then the returned array
* \(b_0, ..., b_{n-1}\) satisfies the identity
* \(\sum_{i=0}^{n-1} b_i x^i = \sum_{i=0}^{n-1} a_i (x + \Delta)^i\) for all \(x\).
* </p>
* <p>
* This method is a modified version of the method with the same name
* in Apache Commons Math {@code PolynomialsUtils} class, simply changing
* computation of binomial coefficients so degrees higher than 66 can be used.
* </p>
*
* @param coefficients Coefficients of the original polynomial.
* @param shift Shift value.
* @return the coefficients \(b_i\) of the shifted
* polynomial.
*/
public static double[] shift(final double[] coefficients,
final double shift) {
final int dp1 = coefficients.length;
final double[] newCoefficients = new double[dp1];
// Pascal triangle.
final double[][] coeff = new double[dp1][dp1];
coeff[0][0] = 1;
for (int i = 1; i < dp1; i++) {
coeff[i][0] = 1;
for (int j = 1; j < i; j++) {
coeff[i][j] = coeff[i - 1][j - 1] + coeff[i - 1][j];
}
coeff[i][i] = 1;
}
// First polynomial coefficient.
double shiftI = 1;
for (int i = 0; i < dp1; i++) {
newCoefficients[0] += coefficients[i] * shiftI;
shiftI *= shift;
}
// Superior order.
final int d = dp1 - 1;
for (int i = 0; i < d; i++) {
double shiftJmI = 1;
for (int j = i; j < d; j++) {
newCoefficients[i + 1] += coeff[j + 1][j - i] * coefficients[j + 1] * shiftJmI;
shiftJmI *= shift;
}
}
return newCoefficients;
}
/** Generate recurrence coefficients.
*
* @param rho ρ value
......
......@@ -22,6 +22,10 @@
<body>
<release version="7.2" date="TBC"
description="">
<action dev="luc" type="fix">
Fixed Newcomb operators generation in DSST for high degree gravity fields.
Fixes issue #237
</action>
<action dev="luc" type="update">
Improved tuning of DSST zonal force models. Users can now tune max degree,
max eccentricity power and max frequency in true longitude for short
......
......@@ -44,6 +44,7 @@ import org.orekit.bodies.OneAxisEllipsoid;
import org.orekit.errors.OrekitException;
import org.orekit.forces.drag.Atmosphere;
import org.orekit.forces.drag.HarrisPriester;
import org.orekit.forces.gravity.potential.GRGSFormatReader;
import org.orekit.forces.gravity.potential.GravityFieldFactory;
import org.orekit.forces.gravity.potential.ICGEMFormatReader;
import org.orekit.forces.gravity.potential.TideSystem;
......@@ -79,6 +80,7 @@ import org.orekit.time.TimeComponents;
import org.orekit.time.TimeScale;
import org.orekit.time.TimeScalesFactory;
import org.orekit.utils.Constants;
import org.orekit.utils.IERSConventions;
import org.orekit.utils.PVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinates;
......@@ -86,6 +88,35 @@ public class DSSTPropagatorTest {
private DSSTPropagator dsstProp;
@Test
public void testHighDegreesSetting() throws OrekitException {
Utils.setDataRoot("regular-data:potential/grgs-format");
GravityFieldFactory.addPotentialCoefficientsReader(new GRGSFormatReader("grim4s4_gr", true));
int earthDegree = 36;
int earthOrder = 36;
final UnnormalizedSphericalHarmonicsProvider provider =
GravityFieldFactory.getUnnormalizedProvider(earthDegree,
earthOrder);
final org.orekit.frames.Frame earthFrame
=FramesFactory.getITRF(IERSConventions.IERS_2010,true); // terrestrial frame
final DSSTForceModel force = new
DSSTTesseral(earthFrame,Constants.WGS84_EARTH_ANGULAR_VELOCITY, provider,
earthDegree, earthOrder, earthDegree, earthOrder);
final Collection<DSSTForceModel> forces = new ArrayList<DSSTForceModel>();
forces.add(force);
TimeScale tai = TimeScalesFactory.getTAI();
AbsoluteDate initialDate = new AbsoluteDate("2015-07-01", tai);
Frame eci = FramesFactory.getGCRF();
KeplerianOrbit orbit = new KeplerianOrbit(
7120000.0, 1.0e-3, FastMath.toRadians(60.0),
FastMath.toRadians(120.0), FastMath.toRadians(47.0),
FastMath.toRadians(12.0),
PositionAngle.TRUE, eci, initialDate, Constants.EIGEN5C_EARTH_MU);
SpacecraftState oscuState = DSSTPropagator.computeOsculatingState(new SpacecraftState(orbit), forces);
Assert.assertEquals(7119927.097122, oscuState.getA(), 0.001);
}
@Test
public void testEphemerisDates() throws OrekitException {
//setup
......
......@@ -72,6 +72,7 @@ public class GammaMnsFunctionTest {
throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
Field precomputedF = GammaMnsFunction.class.getDeclaredField("PRECOMPUTED_RATIOS");
precomputedF.setAccessible(true);
precomputedF.set(null, new double[0]);
new GammaMnsFunction(nMax, 0.5, +1);
double[] orginalPrecomputed = (double[]) precomputedF.get(null);
Assert.assertEquals((nMax + 1) * (nMax + 2) * (4 * nMax + 3) / 6, orginalPrecomputed.length);
......
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