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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
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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
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16   */
17  package org.orekit.propagation.events;
18  
19  import org.hipparchus.geometry.euclidean.threed.Vector3D;
20  import org.hipparchus.ode.events.Action;
21  import org.orekit.bodies.CelestialBodies;
22  import org.orekit.propagation.SpacecraftState;
23  import org.orekit.propagation.events.handlers.EventHandler;
24  import org.orekit.propagation.events.handlers.StopOnDecreasing;
25  import org.orekit.utils.PVCoordinates;
26  import org.orekit.utils.PVCoordinatesProvider;
27  
28  /** Detects when two moving objects come close to each other, as seen from spacecraft.
29   * <p>The main use case for this detector is when the primary object is in fact a ground
30   * station, modeled as a {@link org.orekit.frames.TopocentricFrame} and when the secondary
31   * is the {@link CelestialBodies#getSun() Sun}, for computing
32   * optical reflections.</p>
33   * <p>The default handler behavior is to {@link Action#STOP stop}
34   * propagation when objects enter the proximity zone. This can be changed by calling
35   * {@link #withHandler(EventHandler)} after construction.</p>
36   * @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
37   * @author Luc Maisonobe
38   * @author Thomas Paulet
39   * @since 11.0
40   */
41  public class AngularSeparationFromSatelliteDetector extends AbstractDetector<AngularSeparationFromSatelliteDetector> {
42  
43      /** Primary object, at the center of the proximity zone. */
44      private final PVCoordinatesProvider primaryObject;
45  
46      /** Secondary object, that may come close to the primary, as seen from the spacecraft . */
47      private final PVCoordinatesProvider secondaryObject;
48  
49      /** Proximity angle (rad). */
50      private final double proximityAngle;
51  
52      /** Build a new angular detachment detector.
53       * @param primaryObject primaryObject, at the center of the proximity zone
54       * @param secondaryObject secondaryObject, that may come close to
55       *        the primaryObject as seen from the spacecraft
56       * @param proximityAngle proximity angle as seen from spacecraft, at which events are triggered (rad)
57       */
58      public AngularSeparationFromSatelliteDetector(final PVCoordinatesProvider primaryObject,
59                                                    final PVCoordinatesProvider secondaryObject,
60                                                    final double proximityAngle) {
61          this(EventDetectionSettings.getDefaultEventDetectionSettings(), new StopOnDecreasing(),
62               primaryObject, secondaryObject, proximityAngle);
63      }
64  
65      /** Protected constructor with full parameters.
66       * <p>
67       * This constructor is not public as users are expected to use the builder
68       * API with the various {@code withXxx()} methods to set up the instance
69       * in a readable manner without using a huge amount of parameters.
70       * </p>
71       * @param detectionSettings detection Settings
72       * @param handler event handler to call at event occurrences
73       * @param primaryObject primaryObject at the center of the proximity zone
74       * @param secondaryObject secondaryObject, that may come close to
75       *        the primaryObject as seen from the spacecraft
76       * @param proximityAngle proximity angle as seen from secondaryObject, at which events are triggered (rad)
77       * @since 13.0
78       */
79      protected AngularSeparationFromSatelliteDetector(final EventDetectionSettings detectionSettings,
80                                                       final EventHandler handler,
81                                                       final PVCoordinatesProvider primaryObject,
82                                                       final PVCoordinatesProvider secondaryObject,
83                                                       final double proximityAngle) {
84          super(detectionSettings, handler);
85          this.primaryObject         = primaryObject;
86          this.secondaryObject       = secondaryObject;
87          this.proximityAngle = proximityAngle;
88      }
89  
90      /** {@inheritDoc} */
91      @Override
92      protected AngularSeparationFromSatelliteDetector create(final EventDetectionSettings detectionSettings,
93                                                              final EventHandler newHandler) {
94          return new AngularSeparationFromSatelliteDetector(detectionSettings, newHandler,
95                                               primaryObject, secondaryObject, proximityAngle);
96      }
97  
98      /** Get the primaryObject, at the center of the proximity zone.
99       * @return primaryObject
100      */
101     public PVCoordinatesProvider getPrimaryObject() {
102         return primaryObject;
103     }
104 
105     /** Get the secondaryObject.
106      * @return secondaryObject
107      */
108     public PVCoordinatesProvider getSecondaryObject() {
109         return secondaryObject;
110     }
111 
112     /** Get the proximity angle (rad).
113      * @return the proximity angle
114      */
115     public double getProximityAngle() {
116         return proximityAngle;
117     }
118 
119     /** Compute the value of the switching function.
120      * <p>
121      * This function measures the angular separation between primary and secondary objects
122      * as seen from the spacecraft minus the proximity angle. It therefore triggers
123      * decreasing events when the secondary object enters the proximity zone and increasing
124      * events when it leaves the proximity zone.
125      * </p>
126      * <p>
127      * No shadowing effect is taken into account, so this method is computed and
128      * may trigger events even when the secondary object is behind the primary.
129      * If such effects must be taken into account the
130      * detector must be associated with a {@link EventEnablingPredicateFilter predicate
131      * filter} where the {@link EnablingPredicate predicate function} is based on eclipse conditions.
132      * </p>
133      * @param s the current state information: date, kinematics, attitude
134      * @return value of the switching function
135      */
136     public double g(final SpacecraftState s) {
137         final PVCoordinates sPV = s.getPVCoordinates();
138         final Vector3D primaryPos   = primaryObject  .getPosition(s.getDate(), s.getFrame());
139         final Vector3D secondaryPos = secondaryObject.getPosition(s.getDate(), s.getFrame());
140         final double separation = Vector3D.angle(primaryPos.subtract(sPV.getPosition()),
141                                                  secondaryPos.subtract(sPV.getPosition()));
142         return separation - proximityAngle;
143     }
144 
145 }