TCGScale.java

  1. /* Copyright 2002-2022 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. import org.hipparchus.CalculusFieldElement;

  19. /** Geocentric Coordinate Time.
  20.  * <p>Coordinate time at the center of mass of the Earth.
  21.  * This time scale depends linearly from {@link TTScale Terrestrial Time}.</p>
  22.  * <p>This is intended to be accessed thanks to {@link TimeScales},
  23.  * so there is no public constructor.</p>
  24.  * @author Luc Maisonobe
  25.  * @see AbsoluteDate
  26.  */
  27. public class TCGScale implements TimeScale {

  28.     /** Serializable UID. */
  29.     private static final long serialVersionUID = 20131209L;

  30.     /** LG rate. */
  31.     private static final double LG_RATE = 6.969290134e-10;

  32.     /** Reference date for TCG.
  33.      * <p>The reference date is such that the four following instants are equal:</p>
  34.      * <ul>
  35.      *   <li>1977-01-01T00:00:32.184 TT</li>
  36.      *   <li>1977-01-01T00:00:32.184 TCG</li>
  37.      *   <li>1977-01-01T00:00:32.184 TCB</li>
  38.      *   <li>1977-01-01T00:00:00.000 TAI</li>
  39.      * </ul>
  40.      */
  41.     private final AbsoluteDate referenceDate;

  42.     /** Offset between TT and TAI scales. */
  43.     private final double ttOffset;

  44.     /**
  45.      * Package private constructor for the factory.
  46.      *
  47.      * @param tt  TT time scale.
  48.      * @param tai TAI time scale.
  49.      */
  50.     TCGScale(final TimeScale tt, final TimeScale tai) {
  51.         referenceDate = new AbsoluteDate(1977, 01, 01, tai);
  52.         ttOffset = tt.offsetFromTAI(referenceDate);
  53.     }

  54.     /** {@inheritDoc} */
  55.     @Override
  56.     public double offsetFromTAI(final AbsoluteDate date) {
  57.         return ttOffset + LG_RATE * date.durationFrom(referenceDate);
  58.     }

  59.     /** {@inheritDoc} */
  60.     @Override
  61.     public <T extends CalculusFieldElement<T>> T offsetFromTAI(final FieldAbsoluteDate<T> date) {
  62.         return date.durationFrom(referenceDate).multiply(LG_RATE).add(ttOffset);
  63.     }

  64.     /** {@inheritDoc} */
  65.     public String getName() {
  66.         return "TCG";
  67.     }

  68.     /** {@inheritDoc} */
  69.     public String toString() {
  70.         return getName();
  71.     }

  72. }