1   /* Copyright 2002-2019 CS Systèmes d'Information
2    * Licensed to CS Systèmes d'Information (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.RealFieldElement;
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      /** Serializable UID. */
34      private static final long serialVersionUID = 20131209L;
35  
36      /** UTC scale. */
37      private final UTCScale utc;
38  
39      /** EOP history. */
40      private final EOPHistory eopHistory;
41  
42      /** Simple constructor.
43       * @param eopHistory user supplied EOP history (may be null)
44       * @param utc UTC time scale
45       */
46      protected UT1Scale(final EOPHistory eopHistory, final UTCScale utc) {
47          this.eopHistory = eopHistory;
48          this.utc        = utc;
49      }
50  
51      /** Get the associated UTC scale.
52       * @return associated UTC scale.
53       * @since 9.1
54       */
55      public UTCScale getUTCScale() {
56          return utc;
57      }
58  
59      /** Get the EOP history.
60       * @return eop history (may be null)
61       */
62      public EOPHistory getEOPHistory() {
63          return eopHistory;
64      }
65  
66      /** {@inheritDoc} */
67      @Override
68      public double offsetFromTAI(final AbsoluteDate date) {
69          final double dtu1        = eopHistory == null ? 0 : eopHistory.getUT1MinusUTC(date);
70          final double utcMinusTai = utc.offsetFromTAI(date);
71          return utcMinusTai + dtu1;
72      }
73  
74      /** {@inheritDoc} */
75      @Override
76      public <T extends RealFieldElement<T>> T offsetFromTAI(final FieldAbsoluteDate<T> date) {
77          final T dtu1        = eopHistory == null ? date.getField().getZero() : eopHistory.getUT1MinusUTC(date);
78          final T utcMinusTai = utc.offsetFromTAI(date);
79          return utcMinusTai.add(dtu1);
80      }
81  
82      /** {@inheritDoc} */
83      public String getName() {
84          return "UT1";
85      }
86  
87      /** {@inheritDoc} */
88      public String toString() {
89          return getName();
90      }
91  
92  }