1   /* Contributed in the public domain.
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 java.io.Serializable;
20  
21  import org.hipparchus.CalculusFieldElement;
22  import org.hipparchus.geometry.euclidean.threed.FieldRotation;
23  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
24  import org.hipparchus.geometry.euclidean.threed.Rotation;
25  import org.hipparchus.geometry.euclidean.threed.RotationConvention;
26  import org.hipparchus.geometry.euclidean.threed.Vector3D;
27  import org.orekit.annotation.DefaultDataContext;
28  import org.orekit.data.DataContext;
29  import org.orekit.errors.OrekitException;
30  import org.orekit.errors.OrekitInternalError;
31  import org.orekit.time.AbsoluteDate;
32  import org.orekit.time.FieldAbsoluteDate;
33  import org.orekit.time.TimeScalarFunction;
34  import org.orekit.time.TimeScales;
35  import org.orekit.utils.IERSConventions;
36  
37  /**
38   * An inertial frame aligned with the ecliptic.
39   * <p>
40   * The IAU defines the ecliptic as "the plane perpendicular to the mean heliocentric
41   * orbital angular momentum vector of the Earth-Moon barycentre in the BCRS (IAU 2006
42   * Resolution B1)." The +z axis is aligned with the angular momentum vector, and the +x
43   * axis is aligned with +x axis of {@link Frames#getMOD(IERSConventions) MOD}.
44   * </p>
45   *
46   * <p>
47   * This implementation agrees with the JPL 406 ephemerides to within 0.5 arc seconds.
48   * </p>
49   *
50   * @since 7.0
51   */
52  public class EclipticProvider implements TransformProvider {
53  
54      /** Serializable UID. */
55      private static final long serialVersionUID = 20140516L;
56  
57      /** IERS conventions. */
58      private final IERSConventions conventions;
59  
60      /** the obliquity of the ecliptic, in radians as a function of time. */
61      private final transient TimeScalarFunction obliquity;
62  
63      /**
64       * Create a transform provider from MOD to an ecliptically aligned frame.
65       *
66       * <p>This constructor uses the {@link DataContext#getDefault() default data context}.
67       *
68       * @param conventions IERS conventions
69       * @see #EclipticProvider(IERSConventions, TimeScales)
70       */
71      @DefaultDataContext
72      public EclipticProvider(final IERSConventions conventions) {
73          this(conventions, DataContext.getDefault().getTimeScales());
74      }
75  
76      /**
77       * Create a transform provider from MOD to an ecliptically aligned frame.
78       * @param conventions IERS conventions
79       * @param timeScales to use in computing the transformation.
80       * @since 10.1
81       */
82      public EclipticProvider(final IERSConventions conventions,
83                              final TimeScales timeScales) {
84          this.conventions = conventions;
85          this.obliquity   = conventions.getMeanObliquityFunction(timeScales);
86      }
87  
88      @Override
89      public Transform getTransform(final AbsoluteDate date) {
90          //mean obliquity of date
91          final double epsA = obliquity.value(date);
92          return new Transform(date, new Rotation(Vector3D.MINUS_I, epsA, RotationConvention.VECTOR_OPERATOR));
93      }
94  
95      @Override
96      public <T extends CalculusFieldElement<T>> FieldTransform<T> getTransform(final FieldAbsoluteDate<T> date) {
97          //mean obliquity of date
98          final T epsA = obliquity.value(date);
99          return new FieldTransform<>(date, new FieldRotation<>(FieldVector3D.getMinusI(date.getField()),
100                                                               epsA,
101                                                               RotationConvention.VECTOR_OPERATOR));
102     }
103 
104     /** Replace the instance with a data transfer object for serialization.
105      * <p>
106      * This intermediate class serializes only the frame key.
107      * </p>
108      * @return data transfer object that will be serialized
109      */
110     @DefaultDataContext
111     private Object writeReplace() {
112         return new DataTransferObject(conventions);
113     }
114 
115     /** Internal class used only for serialization. */
116     @DefaultDataContext
117     private static class DataTransferObject implements Serializable {
118 
119         /** Serializable UID. */
120         private static final long serialVersionUID = 20140516L;
121 
122         /** IERS conventions. */
123         private final IERSConventions conventions;
124 
125         /** Simple constructor.
126          * @param conventions IERS conventions
127          */
128         DataTransferObject(final IERSConventions conventions) {
129             this.conventions = conventions;
130         }
131 
132         /** Replace the deserialized data transfer object with a {@link EclipticProvider}.
133          * @return replacement {@link EclipticProvider}
134          */
135         private Object readResolve() {
136             try {
137                 // retrieve a transform
138                 return new EclipticProvider(conventions);
139             } catch (OrekitException oe) {
140                 throw new OrekitInternalError(oe);
141             }
142         }
143 
144     }
145 
146 }