DSSTGradientConverter.java
/* Copyright 2002-2022 CS GROUP
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* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
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*
* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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package org.orekit.propagation.semianalytical.dsst;
import java.util.ArrayList;
import java.util.List;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.analysis.differentiation.GradientField;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.attitudes.FieldAttitude;
import org.orekit.orbits.FieldEquinoctialOrbit;
import org.orekit.orbits.FieldOrbit;
import org.orekit.orbits.PositionAngle;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.integration.AbstractGradientConverter;
import org.orekit.propagation.semianalytical.dsst.forces.DSSTForceModel;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.FieldAngularCoordinates;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.TimeStampedFieldAngularCoordinates;
/** Converter for states and parameters arrays.
* @author Luc Maisonobe
* @author Bryan Cazabonne
* @since 10.2
*/
class DSSTGradientConverter extends AbstractGradientConverter {
/** Fixed dimension of the state. */
private static final int FREE_STATE_PARAMETERS = 6;
/** States with various number of additional parameters for force models. */
private final List<FieldSpacecraftState<Gradient>> gStates;
/** Simple constructor.
* @param state regular state
* @param provider provider to use if attitude needs to be recomputed
*/
DSSTGradientConverter(final SpacecraftState state, final AttitudeProvider provider) {
super(FREE_STATE_PARAMETERS);
// equinoctial parameters always has derivatives
final Gradient sma = Gradient.variable(FREE_STATE_PARAMETERS, 0, state.getA());
final Gradient ex = Gradient.variable(FREE_STATE_PARAMETERS, 1, state.getEquinoctialEx());
final Gradient ey = Gradient.variable(FREE_STATE_PARAMETERS, 2, state.getEquinoctialEy());
final Gradient hx = Gradient.variable(FREE_STATE_PARAMETERS, 3, state.getHx());
final Gradient hy = Gradient.variable(FREE_STATE_PARAMETERS, 4, state.getHy());
final Gradient l = Gradient.variable(FREE_STATE_PARAMETERS, 5, state.getLM());
final Gradient gMu = Gradient.constant(FREE_STATE_PARAMETERS, state.getMu());
// date
final AbsoluteDate date = state.getDate();
final FieldAbsoluteDate<Gradient> dateField = new FieldAbsoluteDate<>(sma.getField(), date);
// mass never has derivatives
final Gradient gM = Gradient.constant(FREE_STATE_PARAMETERS, state.getMass());
final FieldOrbit<Gradient> gOrbit =
new FieldEquinoctialOrbit<>(sma, ex, ey, hx, hy, l,
PositionAngle.MEAN,
state.getFrame(),
dateField,
gMu);
final FieldAttitude<Gradient> gAttitude;
// compute attitude partial derivatives
gAttitude = provider.getAttitude(gOrbit, gOrbit.getDate(), gOrbit.getFrame());
// initialize the list with the state having 0 force model parameters
gStates = new ArrayList<>();
gStates.add(new FieldSpacecraftState<>(gOrbit, gAttitude, gM));
}
/** Get the state with the number of parameters consistent with force model.
* @param forceModel force model
* @return state with the number of parameters consistent with force model
*/
public FieldSpacecraftState<Gradient> getState(final DSSTForceModel forceModel) {
// count the required number of parameters
int nbParams = 0;
for (final ParameterDriver driver : forceModel.getParametersDrivers()) {
if (driver.isSelected()) {
++nbParams;
}
}
// fill in intermediate slots
while (gStates.size() < nbParams + 1) {
gStates.add(null);
}
if (gStates.get(nbParams) == null) {
// it is the first time we need this number of parameters
// we need to create the state
final int freeParameters = FREE_STATE_PARAMETERS + nbParams;
final FieldSpacecraftState<Gradient> s0 = gStates.get(0);
final FieldAbsoluteDate<Gradient> date = new FieldAbsoluteDate<>(GradientField.getField(freeParameters),
s0.getDate().toAbsoluteDate());
// orbit
final FieldOrbit<Gradient> gOrbit =
new FieldEquinoctialOrbit<>(extend(s0.getA(), freeParameters),
extend(s0.getEquinoctialEx(), freeParameters),
extend(s0.getEquinoctialEy(), freeParameters),
extend(s0.getHx(), freeParameters),
extend(s0.getHy(), freeParameters),
extend(s0.getLM(), freeParameters),
PositionAngle.MEAN,
s0.getFrame(), date,
extend(s0.getMu(), freeParameters));
// attitude
final FieldAngularCoordinates<Gradient> ac0 = s0.getAttitude().getOrientation();
final FieldAttitude<Gradient> gAttitude =
new FieldAttitude<>(s0.getAttitude().getReferenceFrame(),
new TimeStampedFieldAngularCoordinates<>(gOrbit.getDate(),
extend(ac0.getRotation(), freeParameters),
extend(ac0.getRotationRate(), freeParameters),
extend(ac0.getRotationAcceleration(), freeParameters)));
// mass
final Gradient gM = extend(s0.getMass(), freeParameters);
gStates.set(nbParams, new FieldSpacecraftState<>(gOrbit, gAttitude, gM));
}
return gStates.get(nbParams);
}
/** Get the force model parameters.
* @param state state as returned by {@link #getState(DSSTForceModel)}
* @param forceModel force model associated with the parameters
* @return force model parameters
*/
public Gradient[] getParameters(final FieldSpacecraftState<Gradient> state,
final DSSTForceModel forceModel) {
final int freeParameters = state.getA().getFreeParameters();
final List<ParameterDriver> drivers = forceModel.getParametersDrivers();
final Gradient[] parameters = new Gradient[drivers.size()];
int index = FREE_STATE_PARAMETERS;
int i = 0;
for (ParameterDriver driver : drivers) {
parameters[i++] = driver.isSelected() ?
Gradient.variable(freeParameters, index++, driver.getValue()) :
Gradient.constant(freeParameters, driver.getValue());
}
return parameters;
}
}