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3    * contributor license agreements.  See the NOTICE file distributed with
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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
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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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17  package org.orekit.propagation.events;
18  
19  import org.hipparchus.analysis.differentiation.UnivariateDerivative2;
20  import org.orekit.bodies.BodyShape;
21  import org.orekit.bodies.FieldGeodeticPoint;
22  import org.orekit.bodies.OneAxisEllipsoid;
23  import org.orekit.propagation.SpacecraftState;
24  import org.orekit.propagation.events.handlers.EventHandler;
25  import org.orekit.propagation.events.handlers.StopOnIncreasing;
26  
27  /** Detector for geographic longitude extremum.
28   * <p>This detector identifies when a spacecraft reaches its
29   * extremum longitudes with respect to a central body.</p>
30   * @author Luc Maisonobe
31   * @since 7.1
32   */
33  public class LongitudeExtremumDetector extends AbstractDetector<LongitudeExtremumDetector> {
34  
35      /** Body on which the longitude is defined. */
36      private OneAxisEllipsoid body;
37  
38      /** Build a new detector.
39       * <p>The new instance uses default values for maximal checking interval
40       * ({@link #DEFAULT_MAX_CHECK}) and convergence threshold ({@link
41       * #DEFAULT_THRESHOLD}).</p>
42       * @param body body on which the longitude is defined
43       */
44      public LongitudeExtremumDetector(final OneAxisEllipsoid body) {
45          this(DEFAULT_MAX_CHECK, DEFAULT_THRESHOLD, body);
46      }
47  
48      /** Build a detector.
49       * @param maxCheck maximal checking interval (s)
50       * @param threshold convergence threshold (s)
51       * @param body body on which the longitude is defined
52       */
53      public LongitudeExtremumDetector(final double maxCheck, final double threshold,
54                                      final OneAxisEllipsoid body) {
55          this(new EventDetectionSettings(maxCheck, threshold, DEFAULT_MAX_ITER), new StopOnIncreasing(),
56               body);
57      }
58  
59      /** Protected constructor with full parameters.
60       * <p>
61       * This constructor is not public as users are expected to use the builder
62       * API with the various {@code withXxx()} methods to set up the instance
63       * in a readable manner without using a huge amount of parameters.
64       * </p>
65       * @param detectionSettings event detection settings
66       * @param handler event handler to call at event occurrences
67       * @param body body on which the longitude is defined
68       * @since 13.0
69       */
70      protected LongitudeExtremumDetector(final EventDetectionSettings detectionSettings, final EventHandler handler,
71                                          final OneAxisEllipsoid body) {
72          super(detectionSettings, handler);
73          this.body = body;
74      }
75  
76      /** {@inheritDoc} */
77      @Override
78      protected LongitudeExtremumDetector create(final EventDetectionSettings detectionSettings,
79                                                 final EventHandler newHandler) {
80          return new LongitudeExtremumDetector(detectionSettings, newHandler, body);
81      }
82  
83      /** Get the body on which the geographic zone is defined.
84       * @return body on which the geographic zone is defined
85       */
86      public BodyShape getBody() {
87          return body;
88      }
89  
90      /** Compute the value of the detection function.
91       * <p>
92       * The value is the spacecraft longitude time derivative.
93       * </p>
94       * @param s the current state information: date, kinematics, attitude
95       * @return spacecraft longitude time derivative
96       */
97      public double g(final SpacecraftState s) {
98  
99          // convert state to geodetic coordinates
100         final FieldGeodeticPoint<UnivariateDerivative2> gp =
101                         body.transform(s.getPVCoordinates(), s.getFrame(), s.getDate());
102 
103         // longitude time derivative
104         return gp.getLongitude().getFirstDerivative();
105 
106     }
107 
108 }