TDBScale.java
/* Copyright 2002-2022 CS GROUP
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* 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,
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*/
package org.orekit.time;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.util.FastMath;
import org.orekit.utils.Constants;
/** Barycentric Dynamic Time.
* <p>Time used to take account of time dilation when calculating orbits of planets,
* asteroids, comets and interplanetary spacecraft in the Solar system. It was based
* on a Dynamical time scale but was not well defined and not rigorously correct as
* a relativistic time scale. It was subsequently deprecated in favour of
* Barycentric Coordinate Time (TCB), but at the 2006 General Assembly of the
* International Astronomical Union TDB was rehabilitated by making it a specific
* fixed linear transformation of TCB.</p>
* <p>By convention, TDB = TT + 0.001658 sin(g) + 0.000014 sin(2g)seconds
* where g = 357.53 + 0.9856003 (JD - 2451545) degrees.</p>
* @author Aude Privat
*/
public class TDBScale implements TimeScale {
/** Serializable UID. */
private static final long serialVersionUID = 20131209L;
/** Constant term for g angle. */
private static final double G0 = 357.53;
/** Slope term for g angle. */
private static final double G1 = 0.9856003;
/** Factor for sin(g). */
private static final double SIN_G_FACTOR = 0.001658;
/** Factor for sin(2g). */
private static final double SIN_2G_FACTOR = 0.000014;
/** TT time scale. */
private final TimeScale tt;
/** Reference Epoch. */
private final AbsoluteDate j2000Epoch;
/**
* Package private constructor for the factory.
*
* @param tt TT time scale.
* @param j2000Epoch reference date for this time scale.
*/
TDBScale(final TimeScale tt, final AbsoluteDate j2000Epoch) {
this.tt = tt;
this.j2000Epoch = j2000Epoch;
}
/** {@inheritDoc} */
@Override
public double offsetFromTAI(final AbsoluteDate date) {
final double dtDays = date.durationFrom(j2000Epoch) / Constants.JULIAN_DAY;
final double g = FastMath.toRadians(G0 + G1 * dtDays);
return tt.offsetFromTAI(date) + (SIN_G_FACTOR * FastMath.sin(g) + SIN_2G_FACTOR * FastMath.sin(2 * g));
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> T offsetFromTAI(final FieldAbsoluteDate<T> date) {
final T dtDays = date.durationFrom(j2000Epoch).divide(Constants.JULIAN_DAY);
final T g = dtDays.multiply(G1).add(G0).multiply(dtDays.getPi().divide(180));
return tt.offsetFromTAI(date).
add(g.sin().multiply(SIN_G_FACTOR).add(g.multiply(2).sin().multiply(SIN_2G_FACTOR)));
}
/** {@inheritDoc} */
public String getName() {
return "TDB";
}
/** {@inheritDoc} */
public String toString() {
return getName();
}
}