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.frames;
18  
19  import org.hipparchus.geometry.euclidean.threed.Rotation;
20  import org.hipparchus.geometry.euclidean.threed.RotationConvention;
21  import org.hipparchus.geometry.euclidean.threed.Vector3D;
22  import org.hipparchus.util.FastMath;
23  import org.orekit.time.AbsoluteDate;
24  import org.orekit.utils.Constants;
25  
26  /** EME2000 frame : mean equator at J2000.0.
27   * <p>This frame was the standard inertial reference prior to GCRF. It was defined
28   * using Lieske precession-nutation model for Earth. This frame has been superseded
29   * by GCRF which is implicitly defined from a few hundred quasars coordinates.
30   * <p>The transformation between GCRF and EME2000 is a constant rotation bias.</p>
31   * @author Luc Maisonobe
32   */
33  class EME2000Provider extends FixedTransformProvider {
34  
35      /** Obliquity of the ecliptic. */
36      private static final double EPSILON_0 = 84381.448 * Constants.ARC_SECONDS_TO_RADIANS;
37  
38      /** Bias in longitude. */
39      private static final double D_PSI_B = -0.041775 * Constants.ARC_SECONDS_TO_RADIANS;
40  
41      /** Bias in obliquity. */
42      private static final double D_EPSILON_B = -0.0068192 * Constants.ARC_SECONDS_TO_RADIANS;
43  
44      /** Right Ascension of the 2000 equinox in ICRS frame. */
45      private static final double ALPHA_0 = -0.0146 * Constants.ARC_SECONDS_TO_RADIANS;
46  
47      /** Simple constructor.
48       */
49      protected EME2000Provider() {
50  
51          // build the bias transform
52          super(new Transform(AbsoluteDate.ARBITRARY_EPOCH,
53                              new Rotation(Vector3D.PLUS_I, D_EPSILON_B, RotationConvention.VECTOR_OPERATOR).
54                              compose(new Rotation(Vector3D.PLUS_J, -D_PSI_B * FastMath.sin(EPSILON_0), RotationConvention.VECTOR_OPERATOR).
55                                      compose(new Rotation(Vector3D.PLUS_K, -ALPHA_0, RotationConvention.VECTOR_OPERATOR), RotationConvention.VECTOR_OPERATOR),
56                                      RotationConvention.VECTOR_OPERATOR)));
57  
58      }
59  
60  }