1 /* Copyright 2022-2025 Romain Serra
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
18 package org.orekit.propagation.events;
19
20 import org.hipparchus.CalculusFieldElement;
21 import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
22 import org.hipparchus.ode.events.Action;
23 import org.orekit.propagation.FieldSpacecraftState;
24 import org.orekit.propagation.events.handlers.FieldEventHandler;
25 import org.orekit.propagation.events.handlers.FieldStopOnEvent;
26 import org.orekit.utils.FieldPVCoordinatesProvider;
27
28 /**
29 * Detector of specific value for the distance relative to another trajectory (using the Euclidean norm).
30 * <p>
31 * The default implementation behavior is to {@link Action#STOP stop} propagation.
32 * This can be changed by calling {@link #withHandler(org.orekit.propagation.events.handlers.FieldEventHandler)} after construction.
33 * </p>
34 * <p>
35 * As this detector needs two objects (moving relative to each other), it embeds one
36 * {@link org.orekit.utils.FieldPVCoordinatesProvider coordinates provider} for the secondary object and is registered as an event detector in
37 * the propagator of the primary object. The secondary object {@link org.orekit.utils.FieldPVCoordinatesProvider coordinates provider} will
38 * therefore be driven by this detector (and hence by the propagator in which this detector is registered).
39 * </p>
40 * <p>
41 * For efficiency reason during the event search loop, it is recommended to have the secondary provider be an analytical
42 * propagator or an ephemeris. A numerical propagator as a secondary propagator works but is expected to be
43 * computationally costly.
44 * </p>
45 *
46 * @see org.orekit.propagation.FieldPropagator#addEventDetector(FieldEventDetector)
47 * @author Romain Serra
48 * @since 12.1
49 */
50 public class FieldRelativeDistanceDetector<T extends CalculusFieldElement<T>>
51 extends FieldAbstractDetector<FieldRelativeDistanceDetector<T>, T> {
52
53 /**
54 * PVCoordinates provider of the other object used to define relative distance.
55 */
56 private final FieldPVCoordinatesProvider<T> secondaryPVProvider;
57
58 /** Relative distance value triggering detection. */
59 private final T distanceThreshold;
60
61 /**
62 * Constructor with default values.
63 * <p>
64 * By default, the implemented behavior is to {@link Action#STOP stop} propagation at detection.
65 * </p>
66 *
67 * @param secondaryPVProvider PVCoordinates provider of the other object defining relative distance.
68 * @param distanceThreshold Relative distance threshold for event detection
69 */
70 public FieldRelativeDistanceDetector(final FieldPVCoordinatesProvider<T> secondaryPVProvider,
71 final T distanceThreshold) {
72 this(new FieldEventDetectionSettings<>(distanceThreshold.getField(), EventDetectionSettings.getDefaultEventDetectionSettings()),
73 new FieldStopOnEvent<>(), secondaryPVProvider, distanceThreshold);
74 }
75
76 /**
77 * Constructor.
78 * <p>
79 * This constructor is to be used if the user wants to change the default behavior of the detector.
80 * </p>
81 *
82 * @param detectionSettings Detection settings.
83 * @param handler Event handler to call at event occurrences.
84 * @param secondaryPVProvider PVCoordinates provider of the other object defining relative distance.
85 * @param distanceThreshold Relative distance threshold for event detection
86 * @see FieldEventHandler
87 * @since 12.2
88 */
89 protected FieldRelativeDistanceDetector(final FieldEventDetectionSettings<T> detectionSettings,
90 final FieldEventHandler<T> handler, final FieldPVCoordinatesProvider<T> secondaryPVProvider,
91 final T distanceThreshold) {
92 super(detectionSettings, handler);
93 this.secondaryPVProvider = secondaryPVProvider;
94 this.distanceThreshold = distanceThreshold;
95 }
96
97 /**
98 * The {@code g} is positive when the relative distance is larger or equal than the threshold,
99 * non-positive otherwise.
100 *
101 * @param s the current state information: date, kinematics, attitude
102 * @return value of the switching function
103 */
104 @Override
105 public T g(final FieldSpacecraftState<T> s) {
106 final FieldVector3D<T> secondaryPosition = getSecondaryPVProvider().getPosition(s.getDate(), s.getFrame());
107 final T relativeDistance = s.getPosition().subtract(secondaryPosition).getNorm();
108 return relativeDistance.subtract(distanceThreshold);
109 }
110
111 /** {@inheritDoc} */
112 @Override
113 protected FieldRelativeDistanceDetector<T> create(final FieldEventDetectionSettings<T> detectionSettings,
114 final FieldEventHandler<T> newHandler) {
115 return new FieldRelativeDistanceDetector<>(detectionSettings, newHandler, secondaryPVProvider,
116 distanceThreshold);
117 }
118
119 /**
120 * Get the secondary position-velocity provider stored in this instance.
121 *
122 * @return the secondary position-velocity provider stored in this instance
123 */
124 public FieldPVCoordinatesProvider<T> getSecondaryPVProvider() {
125 return secondaryPVProvider;
126 }
127
128 /**
129 * Get the relative distance threshold.
130 *
131 * @return threshold triggering detection
132 */
133 public T getDistanceThreshold() {
134 return distanceThreshold;
135 }
136 }