PolynomialParametricAcceleration.java
/* Copyright 2002-2017 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,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.forces;
import org.hipparchus.RealFieldElement;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ParameterDriver;
/** This class implements a {@link AbstractParametricAcceleration parametric acceleration}
* with polynomial signed amplitude.
* @since 9.0
* @author Luc Maisonobe
*/
public class PolynomialParametricAcceleration extends AbstractParametricAcceleration {
/** Acceleration scaling factor.
* <p>
* 2⁻²⁰ is the order of magnitude of third body perturbing acceleration.
* </p>
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private static final double ACCELERATION_SCALE = FastMath.scalb(1.0, -20);
/** Drivers for the polynomial coefficients. */
private final ParameterDriver[] drivers;
/** Reference date for computing polynomials. */
private AbsoluteDate referenceDate;
/** Simple constructor.
* <p>
* The signed amplitude of the acceleration is ∑pₙ(t-t₀)ⁿ, where
* pₙ is parameter {@code n}, t is current date and t₀ is reference date.
* The value t-t₀ is in seconds.
* </p>
* <p>
* The {@code degree + 1} parameters for this model are the polynomial
* coefficients in increasing degree order. Their reference values (used
* also as the initial values) are all set to 0. User can change them before
* starting the propagation (or orbit determination) by calling {@link
* #getParametersDrivers()} and {@link ParameterDriver#setValue(double)}.
* </p>
* @param direction acceleration direction in defining frame
* @param isInertial if true, direction is defined in the same inertial
* frame used for propagation (i.e. {@link SpacecraftState#getFrame()}),
* otherwise direction is defined in spacecraft frame (i.e. using the
* propagation {@link
* org.orekit.propagation.Propagator#setAttitudeProvider(AttitudeProvider)
* attitude law})
* @param prefix prefix to use for parameter drivers
* @param referenceDate reference date for computing polynomials, if null
* the reference date will be automatically set at propagation start
* @param degree polynomial degree (i.e. a value of 0 corresponds to a constant acceleration)
*/
public PolynomialParametricAcceleration(final Vector3D direction, final boolean isInertial,
final String prefix, final AbsoluteDate referenceDate,
final int degree) {
this(direction, isInertial, null, prefix, referenceDate, degree);
}
/** Simple constructor.
* <p>
* The signed amplitude of the acceleration is ∑pₙ(t-t₀)ⁿ, where
* pₙ is parameter {@code n}, t is current date and t₀ is reference date.
* The value t-t₀ is in seconds.
* </p>
* <p>
* The {@code degree + 1} parameters for this model are the polynomial
* coefficients in increasing degree order. Their reference values (used
* also as the initial values) are all set to 0. User can change them before
* starting the propagation (or orbit determination) by calling {@link
* #getParametersDrivers()} and {@link ParameterDriver#setValue(double)}.
* </p>
* @param direction acceleration direction in overridden spacecraft frame
* @param attitudeOverride provider for attitude used to compute acceleration
* direction
* @param prefix prefix to use for parameter drivers
* @param referenceDate reference date for computing polynomials, if null
* the reference date will be automatically set at propagation start
* @param degree polynomial degree (i.e. a value of 0 corresponds to a constant acceleration)
*/
public PolynomialParametricAcceleration(final Vector3D direction, final AttitudeProvider attitudeOverride,
final String prefix, final AbsoluteDate referenceDate,
final int degree) {
this(direction, false, attitudeOverride, prefix, referenceDate, degree);
}
/** Simple constructor.
* @param direction acceleration direction in overridden spacecraft frame
* @param isInertial if true, direction is defined in the same inertial
* frame used for propagation (i.e. {@link SpacecraftState#getFrame()}),
* otherwise direction is defined in spacecraft frame (i.e. using the
* propagation {@link
* org.orekit.propagation.Propagator#setAttitudeProvider(AttitudeProvider)
* attitude law})
* @param attitudeOverride provider for attitude used to compute acceleration
* direction
* @param prefix prefix to use for parameter drivers
* @param referenceDate reference date for computing polynomials, if null
* the reference date will be automatically set at propagation start
* @param degree polynomial degree (i.e. a value of 0 corresponds to a constant acceleration)
*/
private PolynomialParametricAcceleration(final Vector3D direction, final boolean isInertial,
final AttitudeProvider attitudeOverride,
final String prefix, final AbsoluteDate referenceDate,
final int degree) {
super(direction, isInertial, attitudeOverride);
this.referenceDate = referenceDate;
this.drivers = new ParameterDriver[degree + 1];
try {
for (int i = 0; i < drivers.length; ++i) {
drivers[i] = new ParameterDriver(prefix + "[" + i + "]", 0.0, ACCELERATION_SCALE,
Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
}
} catch (OrekitException oe) {
// this should never happen as scale is hard-coded
throw new OrekitInternalError(oe);
}
}
/** {@inheritDoc} */
@Override
public boolean dependsOnPositionOnly() {
return isInertial();
}
/** {@inheritDoc} */
@Override
public void init(final SpacecraftState initialState, final AbsoluteDate target)
throws OrekitException {
if (referenceDate == null) {
referenceDate = initialState.getDate();
}
}
/** {@inheritDoc} */
@Override
protected double signedAmplitude(final SpacecraftState state, final double[] parameters) {
final double dt = state.getDate().durationFrom(referenceDate);
double amplitude = 0;
for (int i = parameters.length - 1; i >= 0; --i) {
amplitude += amplitude * dt + parameters[i];
}
return amplitude;
}
/** {@inheritDoc} */
@Override
protected <T extends RealFieldElement<T>> T signedAmplitude(final FieldSpacecraftState<T> state, final T[] parameters) {
final T dt = state.getDate().durationFrom(referenceDate);
T amplitude = dt.getField().getZero();
for (int i = parameters.length - 1; i >= 0; --i) {
amplitude = amplitude.add(amplitude.multiply(dt).add(parameters[i]));
}
return amplitude;
}
/** {@inheritDoc} */
@Override
public ParameterDriver[] getParametersDrivers() {
return drivers.clone();
}
}