TDBScale.java
- /* Copyright 2002-2022 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.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();
- }
- }