TEMEProvider.java
/* Copyright 2002-2020 CS Group
* Licensed to CS Group (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.frames;
import java.io.Serializable;
import org.hipparchus.RealFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldRotation;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Rotation;
import org.hipparchus.geometry.euclidean.threed.RotationConvention;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.data.DataContext;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.time.TimeScalarFunction;
import org.orekit.time.TimeScales;
import org.orekit.time.TimeVectorFunction;
import org.orekit.utils.IERSConventions;
/** True Equator Mean Equinox Frame.
* <p>This frame is used for the SGP4 model in TLE propagation. This frame has <em>no</em>
* official definition and there are some ambiguities about whether it should be used
* as "of date" or "of epoch". This frame should therefore be used <em>only</em> for
* TLE propagation and not for anything else, as recommended by the CCSDS Orbit Data Message
* blue book.</p>
* @author Luc Maisonobe
*/
class TEMEProvider implements EOPBasedTransformProvider {
/** Serializable UID. */
private static final long serialVersionUID = 20131209L;
/** Conventions. */
private final IERSConventions conventions;
/** EOP history. */
private final EOPHistory eopHistory;
/** Function computing the mean obliquity. */
private final transient TimeScalarFunction obliquityFunction;
/** Function computing the nutation angles. */
private final transient TimeVectorFunction nutationFunction;
/**
* Simple constructor.
* @param conventions IERS conventions to apply
* @param eopHistory EOP history or {@code null} if no corrections should be
* applied.
* @param timeScales other time scales used in computing the transform.
*/
TEMEProvider(final IERSConventions conventions,
final EOPHistory eopHistory,
final TimeScales timeScales) {
this.conventions = conventions;
this.eopHistory = eopHistory;
this.obliquityFunction = conventions.getMeanObliquityFunction(timeScales);
this.nutationFunction = conventions.getNutationFunction(timeScales);
}
/**
* Private constructor.
*
* @param conventions IERS conventions to apply
* @param eopHistory EOP history
* @param obliquityFunction to use.
* @param nutationFunction to use.
*/
private TEMEProvider(final IERSConventions conventions,
final EOPHistory eopHistory,
final TimeScalarFunction obliquityFunction,
final TimeVectorFunction nutationFunction) {
this.conventions = conventions;
this.eopHistory = eopHistory;
this.obliquityFunction = obliquityFunction;
this.nutationFunction = nutationFunction;
}
/** {@inheritDoc} */
@Override
public EOPHistory getEOPHistory() {
return eopHistory;
}
/** {@inheritDoc} */
@Override
public TEMEProvider getNonInterpolatingProvider() {
return new TEMEProvider(conventions, eopHistory.getNonInterpolatingEOPHistory(),
obliquityFunction, nutationFunction);
}
/** {@inheritDoc} */
@Override
public Transform getTransform(final AbsoluteDate date) {
final double eqe = getEquationOfEquinoxes(date);
return new Transform(date, new Rotation(Vector3D.PLUS_K, eqe, RotationConvention.FRAME_TRANSFORM));
}
/** {@inheritDoc} */
@Override
public <T extends RealFieldElement<T>> FieldTransform<T> getTransform(final FieldAbsoluteDate<T> date) {
final T eqe = getEquationOfEquinoxes(date);
return new FieldTransform<>(date, new FieldRotation<>(FieldVector3D.getPlusK(date.getField()),
eqe,
RotationConvention.FRAME_TRANSFORM));
}
/** Get the Equation of the Equinoxes at the current date.
* @param date the date
* @return equation of the equinoxes
*/
private double getEquationOfEquinoxes(final AbsoluteDate date) {
// compute nutation angles
final double[] angles = nutationFunction.value(date);
// nutation in longitude
double dPsi = angles[0];
if (eopHistory != null) {
// apply the corrections for the nutation parameters
final double[] correction = eopHistory.getEquinoxNutationCorrection(date);
dPsi += correction[0];
}
// mean obliquity of ecliptic
final double moe = obliquityFunction.value(date);
// original definition of equation of equinoxes
final double eqe = dPsi * FastMath.cos(moe);
// apply correction if needed
return eqe + angles[2];
}
/** Get the Equation of the Equinoxes at the current date.
* @param date the date
* @param <T> type of the field elements
* @return equation of the equinoxes
*/
private <T extends RealFieldElement<T>> T getEquationOfEquinoxes(final FieldAbsoluteDate<T> date) {
// compute nutation angles
final T[] angles = nutationFunction.value(date);
// nutation in longitude
T dPsi = angles[0];
if (eopHistory != null) {
// apply the corrections for the nutation parameters
final T[] correction = eopHistory.getEquinoxNutationCorrection(date);
dPsi = dPsi.add(correction[0]);
}
// mean obliquity of ecliptic
final T moe = obliquityFunction.value(date);
// original definition of equation of equinoxes
final T eqe = dPsi.multiply(moe.cos());
// apply correction if needed
return eqe.add(angles[2]);
}
/** Replace the instance with a data transfer object for serialization.
* <p>
* This intermediate class serializes only the frame key.
* </p>
* @return data transfer object that will be serialized
*/
@DefaultDataContext
private Object writeReplace() {
return new DataTransferObject(conventions, eopHistory);
}
/** Internal class used only for serialization. */
@DefaultDataContext
private static class DataTransferObject implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20131209L;
/** Conventions. */
private final IERSConventions conventions;
/** EOP history. */
private final EOPHistory eopHistory;
/** Simple constructor.
* @param conventions IERS conventions to apply
* @param eopHistory EOP history
*/
DataTransferObject(final IERSConventions conventions, final EOPHistory eopHistory) {
this.conventions = conventions;
this.eopHistory = eopHistory;
}
/** Replace the deserialized data transfer object with a {@link TEMEProvider}.
* @return replacement {@link TEMEProvider}
*/
private Object readResolve() {
try {
// retrieve a managed frame
return new TEMEProvider(conventions, eopHistory,
DataContext.getDefault().getTimeScales());
} catch (OrekitException oe) {
throw new OrekitInternalError(oe);
}
}
}
}