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  import org.orekit.frames.EOPHistory;
21  
22  /** Universal Time 1.
23   * <p>UT1 is a time scale directly linked to the actual rotation of the Earth.
24   * It is an irregular scale, reflecting Earth irregular rotation rate. The offset
25   * between UT1 and {@link UTCScale UTC} is found in the Earth Orientation
26   * Parameters published by IERS.</p>
27   * @author Luc Maisonobe
28   * @see AbsoluteDate
29   * @since 5.1
30   */
31  public class UT1Scale implements TimeScale {
32  
33      /** UTC scale. */
34      private final UTCScale utc;
35  
36      /** EOP history. */
37      private final EOPHistory eopHistory;
38  
39      /** Simple constructor.
40       * @param eopHistory user supplied EOP history (may be null)
41       * @param utc UTC time scale
42       */
43      protected UT1Scale(final EOPHistory eopHistory, final UTCScale utc) {
44          this.eopHistory = eopHistory;
45          this.utc        = utc;
46      }
47  
48      /** Get the associated UTC scale.
49       * @return associated UTC scale.
50       * @since 9.1
51       */
52      public UTCScale getUTCScale() {
53          return utc;
54      }
55  
56      /** Get the EOP history.
57       * @return eop history (may be null)
58       */
59      public EOPHistory getEOPHistory() {
60          return eopHistory;
61      }
62  
63      /** {@inheritDoc} */
64      @Override
65      public TimeOffset offsetFromTAI(final AbsoluteDate date) {
66          final double    dtu1        = eopHistory == null ? 0 : eopHistory.getUT1MinusUTC(date);
67          final TimeOffset utcMinusTai = utc.offsetFromTAI(date);
68          return utcMinusTai.add(new TimeOffset(dtu1));
69      }
70  
71      /** {@inheritDoc} */
72      @Override
73      public <T extends CalculusFieldElement<T>> T offsetFromTAI(final FieldAbsoluteDate<T> date) {
74          final T dtu1        = eopHistory == null ? date.getField().getZero() : eopHistory.getUT1MinusUTC(date);
75          final T utcMinusTai = utc.offsetFromTAI(date);
76          return utcMinusTai.add(dtu1);
77      }
78  
79      /** {@inheritDoc} */
80      public String getName() {
81          return "UT1";
82      }
83  
84      /** {@inheritDoc} */
85      public String toString() {
86          return getName();
87      }
88  
89  }