1   /* Copyright 2002-2025 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  
21  /** Barycentric Coordinate Time.
22   * <p>Coordinate time at the center of mass of the Solar System.
23   * This time scale depends linearly from {@link TDBScale Barycentric Dynamical Time}.</p>
24   * <p>This is intended to be accessed thanks to {@link TimeScales},
25   * so there is no public constructor.</p>
26   * @author Luc Maisonobe
27   * @see AbsoluteDate
28   */
29  public class TCBScale implements TimeScale {
30  
31      /** LG rate. */
32      private static final double LB_RATE = 1.550519768e-8;
33  
34      /** Reference date for TCB.
35       * <p>The reference date is such that the four following instants are equal:</p>
36       * <ul>
37       *   <li>1977-01-01T00:00:32.184 TT</li>
38       *   <li>1977-01-01T00:00:32.184 TCG</li>
39       *   <li>1977-01-01T00:00:32.184 TCB</li>
40       *   <li>1977-01-01T00:00:00.000 TAI</li>
41       * </ul>
42       */
43      private final AbsoluteDate referenceDate;
44  
45      /** Barycentric dynamic time scale. */
46      private final TDBScale tdb;
47  
48      /**
49       * Package private constructor for the factory.
50       *
51       * @param tdb Barycentric dynamic time scale
52       * @param tai TAI time scale.
53       */
54      TCBScale(final TDBScale tdb, final TimeScale tai) {
55          this.tdb = tdb;
56          referenceDate = new AbsoluteDate(1977, 1, 1, tai);
57      }
58  
59      /** {@inheritDoc} */
60      @Override
61      public TimeOffset offsetFromTAI(final AbsoluteDate date) {
62          return tdb.offsetFromTAI(date).add(new TimeOffset(LB_RATE * date.durationFrom(referenceDate)));
63      }
64  
65      /** {@inheritDoc} */
66      @Override
67      public <T extends CalculusFieldElement<T>> T offsetFromTAI(final FieldAbsoluteDate<T> date) {
68          return tdb.offsetFromTAI(date).add(date.durationFrom(referenceDate).multiply(LB_RATE));
69      }
70  
71      /** {@inheritDoc} */
72      public String getName() {
73          return "TCB";
74      }
75  
76      /** {@inheritDoc} */
77      public String toString() {
78          return getName();
79      }
80  
81  }