1   /* Copyright 2002-2021 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.attitudes;
18  
19  import org.hipparchus.CalculusFieldElement;
20  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
21  import org.hipparchus.geometry.euclidean.threed.Vector3D;
22  import org.orekit.bodies.BodyShape;
23  import org.orekit.bodies.GeodeticPoint;
24  import org.orekit.frames.FieldTransform;
25  import org.orekit.frames.Frame;
26  import org.orekit.frames.Transform;
27  import org.orekit.time.AbsoluteDate;
28  import org.orekit.time.FieldAbsoluteDate;
29  import org.orekit.utils.FieldPVCoordinatesProvider;
30  import org.orekit.utils.PVCoordinatesProvider;
31  import org.orekit.utils.TimeStampedFieldPVCoordinates;
32  import org.orekit.utils.TimeStampedPVCoordinates;
33  
34  /**
35   * This class handles target pointing attitude provider.
36  
37   * <p>
38   * This class represents the attitude provider where the satellite z axis is
39   * pointing to a ground point target.</p>
40   * <p>
41   * The target position is defined in a body frame specified by the user.
42   * It is important to make sure this frame is consistent.
43   * </p>
44   * <p>
45   * The object <code>TargetPointing</code> is guaranteed to be immutable.
46   * </p>
47   * @see     GroundPointing
48   * @author V&eacute;ronique Pommier-Maurussane
49   */
50  public class TargetPointing extends GroundPointing {
51  
52      /** Target in body frame. */
53      private final Vector3D target;
54  
55      /** Creates a new instance from body frame and target expressed in Cartesian coordinates.
56       * @param inertialFrame frame in which orbital velocities are computed
57       * @param bodyFrame body frame.
58       * @param target target position in body frame
59       * @since 7.1
60       */
61      public TargetPointing(final Frame inertialFrame, final Frame bodyFrame, final Vector3D target) {
62          super(inertialFrame, bodyFrame);
63          this.target = target;
64      }
65  
66      /** Creates a new instance from body shape and target expressed in geodetic coordinates.
67       * @param inertialFrame frame in which orbital velocities are computed
68       * @param targetGeo target defined as a geodetic point in body shape frame
69       * @param shape body shape
70       * @since 7.1
71       */
72      public TargetPointing(final Frame inertialFrame, final GeodeticPoint targetGeo, final BodyShape shape) {
73          super(inertialFrame, shape.getBodyFrame());
74          // Transform target from geodetic coordinates to Cartesian coordinates
75          target = shape.transform(targetGeo);
76      }
77  
78      /** {@inheritDoc} */
79      @Override
80      public TimeStampedPVCoordinates getTargetPV(final PVCoordinatesProvider pvProv,
81                                                  final AbsoluteDate date, final Frame frame) {
82          final Transform t = getBodyFrame().getTransformTo(frame, date);
83          final TimeStampedPVCoordinates pv =
84                  new TimeStampedPVCoordinates(date, target, Vector3D.ZERO, Vector3D.ZERO);
85          return t.transformPVCoordinates(pv);
86      }
87  
88      /** {@inheritDoc} */
89      @Override
90      public <T extends CalculusFieldElement<T>> TimeStampedFieldPVCoordinates<T> getTargetPV(final FieldPVCoordinatesProvider<T> pvProv,
91                                                                                          final FieldAbsoluteDate<T> date, final Frame frame) {
92          final FieldTransform<T> t = getBodyFrame().getTransformTo(frame, date);
93          final FieldVector3D<T> zero = FieldVector3D.getZero(date.getField());
94          final TimeStampedFieldPVCoordinates<T> pv =
95                  new TimeStampedFieldPVCoordinates<>(date, new FieldVector3D<>(date.getField(), target), zero, zero);
96          return t.transformPVCoordinates(pv);
97      }
98  
99  }