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 org.hipparchus.CalculusFieldElement;
20  import org.hipparchus.geometry.euclidean.threed.FieldRotation;
21  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
22  import org.hipparchus.geometry.euclidean.threed.RotationConvention;
23  import org.orekit.annotation.DefaultDataContext;
24  import org.orekit.data.DataContext;
25  import org.orekit.time.FieldAbsoluteDate;
26  import org.orekit.time.TimeScalarFunction;
27  import org.orekit.time.TimeScales;
28  import org.orekit.utils.IERSConventions;
29  
30  /**
31   * An inertial frame aligned with the ecliptic.
32   * <p>
33   * The IAU defines the ecliptic as "the plane perpendicular to the mean heliocentric
34   * orbital angular momentum vector of the Earth-Moon barycentre in the BCRS (IAU 2006
35   * Resolution B1)." The +z axis is aligned with the angular momentum vector, and the +x
36   * axis is aligned with +x axis of {@link Frames#getMOD(IERSConventions) MOD}.
37   * </p>
38   *
39   * <p>
40   * This implementation agrees with the JPL 406 ephemerides to within 0.5 arc seconds.
41   * </p>
42   *
43   * @since 7.0
44   */
45  public class EclipticProvider implements FieldBasedTransformProvider {
46  
47      /** the obliquity of the ecliptic, in radians as a function of time. */
48      private final TimeScalarFunction obliquity;
49  
50      /**
51       * Create a transform provider from MOD to an ecliptically aligned frame.
52       *
53       * <p>This constructor uses the {@link DataContext#getDefault() default data context}.
54       *
55       * @param conventions IERS conventions
56       * @see #EclipticProvider(IERSConventions, TimeScales)
57       */
58      @DefaultDataContext
59      public EclipticProvider(final IERSConventions conventions) {
60          this(conventions, DataContext.getDefault().getTimeScales());
61      }
62  
63      /**
64       * Create a transform provider from MOD to an ecliptically aligned frame.
65       * @param conventions IERS conventions
66       * @param timeScales to use in computing the transformation.
67       * @since 10.1
68       */
69      public EclipticProvider(final IERSConventions conventions,
70                              final TimeScales timeScales) {
71          this.obliquity   = conventions.getMeanObliquityFunction(timeScales);
72      }
73  
74      /** Compute the ecliptic rotation.
75       * @param date current date
76       * @param <T> type of the field elements
77       * @return ecliptic rotation
78       */
79      public <T extends CalculusFieldElement<T>> FieldRotation<T> getRotation(final FieldAbsoluteDate<T> date) {
80          //mean obliquity of date
81          final T epsA = obliquity.value(date);
82          return new FieldRotation<>(FieldVector3D.getMinusI(date.getField()), epsA,
83                                     RotationConvention.VECTOR_OPERATOR);
84      }
85  
86  }