1 /* Copyright 2002-2024 CS GROUP
2 * Licensed to CS GROUP (CS) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * CS licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.orekit.time;
18
19 import org.hipparchus.CalculusFieldElement;
20 import org.hipparchus.util.FastMath;
21 import org.orekit.utils.Constants;
22
23 /** Barycentric Dynamic Time.
24 * <p>Time used to take account of time dilation when calculating orbits of planets,
25 * asteroids, comets and interplanetary spacecraft in the Solar system. It was based
26 * on a Dynamical time scale but was not well defined and not rigorously correct as
27 * a relativistic time scale. It was subsequently deprecated in favour of
28 * Barycentric Coordinate Time (TCB), but at the 2006 General Assembly of the
29 * International Astronomical Union TDB was rehabilitated by making it a specific
30 * fixed linear transformation of TCB.</p>
31 * <p>By convention, TDB = TT + 0.001658 sin(g) + 0.000014 sin(2g)seconds
32 * where g = 357.53 + 0.9856003 (JD - 2451545) degrees.</p>
33 * @author Aude Privat
34 */
35 public class TDBScale implements TimeScale {
36
37 /** Serializable UID. */
38 private static final long serialVersionUID = 20131209L;
39
40 /** Constant term for g angle. */
41 private static final double G0 = 357.53;
42
43 /** Slope term for g angle. */
44 private static final double G1 = 0.9856003;
45
46 /** Factor for sin(g). */
47 private static final double SIN_G_FACTOR = 0.001658;
48
49 /** Factor for sin(2g). */
50 private static final double SIN_2G_FACTOR = 0.000014;
51
52 /** TT time scale. */
53 private final TimeScale tt;
54
55 /** Reference Epoch. */
56 private final AbsoluteDate j2000Epoch;
57
58 /**
59 * Package private constructor for the factory.
60 *
61 * @param tt TT time scale.
62 * @param j2000Epoch reference date for this time scale.
63 */
64 TDBScale(final TimeScale tt, final AbsoluteDate j2000Epoch) {
65 this.tt = tt;
66 this.j2000Epoch = j2000Epoch;
67 }
68
69 /** {@inheritDoc} */
70 @Override
71 public double offsetFromTAI(final AbsoluteDate date) {
72 final double dtDays = date.durationFrom(j2000Epoch) / Constants.JULIAN_DAY;
73 final double g = FastMath.toRadians(G0 + G1 * dtDays);
74 return tt.offsetFromTAI(date) + (SIN_G_FACTOR * FastMath.sin(g) + SIN_2G_FACTOR * FastMath.sin(2 * g));
75 }
76
77 /** {@inheritDoc} */
78 @Override
79 public <T extends CalculusFieldElement<T>> T offsetFromTAI(final FieldAbsoluteDate<T> date) {
80 final T dtDays = date.durationFrom(j2000Epoch).divide(Constants.JULIAN_DAY);
81 final T g = dtDays.multiply(G1).add(G0).multiply(dtDays.getPi().divide(180));
82 return tt.offsetFromTAI(date).
83 add(g.sin().multiply(SIN_G_FACTOR).add(g.multiply(2).sin().multiply(SIN_2G_FACTOR)));
84 }
85
86 /** {@inheritDoc} */
87 public String getName() {
88 return "TDB";
89 }
90
91 /** {@inheritDoc} */
92 public String toString() {
93 return getName();
94 }
95
96 }