NumericalGradientConverter.java
/* Copyright 2002-2020 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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* the License. You may obtain a copy of the License at
*
* 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.numerical;
import java.util.ArrayList;
import java.util.List;
import org.hipparchus.Field;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.analysis.differentiation.GradientField;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.attitudes.FieldAttitude;
import org.orekit.forces.ForceModel;
import org.orekit.orbits.FieldCartesianOrbit;
import org.orekit.orbits.FieldOrbit;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.integration.AbstractGradientConverter;
import org.orekit.utils.FieldAngularCoordinates;
import org.orekit.utils.FieldPVCoordinates;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.TimeStampedFieldAngularCoordinates;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
/** Converter for states and parameters arrays.
* @author Luc Maisonobe
* @since 10.2
*/
class NumericalGradientConverter extends AbstractGradientConverter {
/** Dimension of the state. */
private final int freeStateParameters;
/** States with various number of additional parameters for force models. */
private final List<FieldSpacecraftState<Gradient>> gStates;
/** Simple constructor.
* @param state regular state
* @param freeStateParameters number of free parameters, either 3 (position) or 6 (position-velocity)
* @param provider provider to use if attitude needs to be recomputed
*/
NumericalGradientConverter(final SpacecraftState state, final int freeStateParameters,
final AttitudeProvider provider) {
super(freeStateParameters);
this.freeStateParameters = freeStateParameters;
// Derivative field
final Field<Gradient> field = GradientField.getField(freeStateParameters);
// position always has derivatives
final Vector3D pos = state.getPVCoordinates().getPosition();
final FieldVector3D<Gradient> posG = new FieldVector3D<>(Gradient.variable(freeStateParameters, 0, pos.getX()),
Gradient.variable(freeStateParameters, 1, pos.getY()),
Gradient.variable(freeStateParameters, 2, pos.getZ()));
// velocity may have derivatives or not
final Vector3D vel = state.getPVCoordinates().getVelocity();
final FieldVector3D<Gradient> velG;
if (freeStateParameters > 3) {
velG = new FieldVector3D<>(Gradient.variable(freeStateParameters, 3, vel.getX()),
Gradient.variable(freeStateParameters, 4, vel.getY()),
Gradient.variable(freeStateParameters, 5, vel.getZ()));
} else {
velG = new FieldVector3D<>(Gradient.constant(freeStateParameters, vel.getX()),
Gradient.constant(freeStateParameters, vel.getY()),
Gradient.constant(freeStateParameters, vel.getZ()));
}
// acceleration never has derivatives
final Vector3D acc = state.getPVCoordinates().getAcceleration();
final FieldVector3D<Gradient> accG = new FieldVector3D<>(Gradient.constant(freeStateParameters, acc.getX()),
Gradient.constant(freeStateParameters, acc.getY()),
Gradient.constant(freeStateParameters, acc.getZ()));
// mass never has derivatives
final Gradient gM = Gradient.constant(freeStateParameters, state.getMass());
final Gradient gMu = Gradient.constant(freeStateParameters, state.getMu());
final FieldOrbit<Gradient> gOrbit =
new FieldCartesianOrbit<>(new TimeStampedFieldPVCoordinates<>(state.getDate(), posG, velG, accG),
state.getFrame(), gMu);
final FieldAttitude<Gradient> gAttitude;
if (freeStateParameters > 3) {
// compute attitude partial derivatives with respect to position/velocity
gAttitude = provider.getAttitude(gOrbit, gOrbit.getDate(), gOrbit.getFrame());
} else {
// force model does not depend on attitude, don't bother recomputing it
gAttitude = new FieldAttitude<>(field, state.getAttitude());
}
// 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 ForceModel 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 = freeStateParameters + nbParams;
final FieldSpacecraftState<Gradient> s0 = gStates.get(0);
// orbit
final FieldPVCoordinates<Gradient> pv0 = s0.getPVCoordinates();
final FieldOrbit<Gradient> gOrbit =
new FieldCartesianOrbit<>(new TimeStampedFieldPVCoordinates<>(s0.getDate().toAbsoluteDate(),
extend(pv0.getPosition(), freeParameters),
extend(pv0.getVelocity(), freeParameters),
extend(pv0.getAcceleration(), freeParameters)),
s0.getFrame(),
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(ForceModel)}
* @param forceModel force model associated with the parameters
* @return force model parameters
*/
public Gradient[] getParameters(final FieldSpacecraftState<Gradient> state,
final ForceModel forceModel) {
final int freeParameters = state.getMass().getFreeParameters();
final ParameterDriver[] drivers = forceModel.getParametersDrivers();
final Gradient[] parameters = new Gradient[drivers.length];
int index = freeStateParameters;
for (int i = 0; i < drivers.length; ++i) {
parameters[i] = drivers[i].isSelected() ?
Gradient.variable(freeParameters, index++, drivers[i].getValue()) :
Gradient.constant(freeParameters, drivers[i].getValue());
}
return parameters;
}
}