1 /* Copyright 2022-2026 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 * @param <T> type of the field elements
47 * @see org.orekit.propagation.FieldPropagator#addEventDetector(FieldEventDetector)
48 * @author Romain Serra
49 * @since 12.1
50 */
51 public class FieldRelativeDistanceDetector<T extends CalculusFieldElement<T>>
52 extends FieldAbstractDetector<FieldRelativeDistanceDetector<T>, T> {
53
54 /**
55 * PVCoordinates provider of the other object used to define relative distance.
56 */
57 private final FieldPVCoordinatesProvider<T> secondaryPVProvider;
58
59 /** Relative distance value triggering detection. */
60 private final T distanceThreshold;
61
62 /**
63 * Constructor with default values.
64 * <p>
65 * By default, the implemented behavior is to {@link Action#STOP stop} propagation at detection.
66 * </p>
67 *
68 * @param secondaryPVProvider PVCoordinates provider of the other object defining relative distance.
69 * @param distanceThreshold Relative distance threshold for event detection
70 */
71 public FieldRelativeDistanceDetector(final FieldPVCoordinatesProvider<T> secondaryPVProvider,
72 final T distanceThreshold) {
73 this(new FieldEventDetectionSettings<>(distanceThreshold.getField(), EventDetectionSettings.getDefaultEventDetectionSettings()),
74 new FieldStopOnEvent<>(), secondaryPVProvider, distanceThreshold);
75 }
76
77 /**
78 * Constructor.
79 * <p>
80 * This constructor is to be used if the user wants to change the default behavior of the detector.
81 * </p>
82 *
83 * @param detectionSettings Detection settings.
84 * @param handler Event handler to call at event occurrences.
85 * @param secondaryPVProvider PVCoordinates provider of the other object defining relative distance.
86 * @param distanceThreshold Relative distance threshold for event detection
87 * @see FieldEventHandler
88 * @since 12.2
89 */
90 protected FieldRelativeDistanceDetector(final FieldEventDetectionSettings<T> detectionSettings,
91 final FieldEventHandler<T> handler, final FieldPVCoordinatesProvider<T> secondaryPVProvider,
92 final T distanceThreshold) {
93 super(detectionSettings, handler);
94 this.secondaryPVProvider = secondaryPVProvider;
95 this.distanceThreshold = distanceThreshold;
96 }
97
98 /**
99 * The {@code g} is positive when the relative distance is larger or equal than the threshold,
100 * non-positive otherwise.
101 *
102 * @param s the current state information: date, kinematics, attitude
103 * @return value of the switching function
104 */
105 @Override
106 public T g(final FieldSpacecraftState<T> s) {
107 final FieldVector3D<T> secondaryPosition = getSecondaryPVProvider().getPosition(s.getDate(), s.getFrame());
108 final T relativeDistance = s.getPosition().subtract(secondaryPosition).getNorm();
109 return relativeDistance.subtract(distanceThreshold);
110 }
111
112 /** {@inheritDoc} */
113 @Override
114 protected FieldRelativeDistanceDetector<T> create(final FieldEventDetectionSettings<T> detectionSettings,
115 final FieldEventHandler<T> newHandler) {
116 return new FieldRelativeDistanceDetector<>(detectionSettings, newHandler, secondaryPVProvider,
117 distanceThreshold);
118 }
119
120 /**
121 * Get the secondary position-velocity provider stored in this instance.
122 *
123 * @return the secondary position-velocity provider stored in this instance
124 */
125 public FieldPVCoordinatesProvider<T> getSecondaryPVProvider() {
126 return secondaryPVProvider;
127 }
128
129 /**
130 * Get the relative distance threshold.
131 *
132 * @return threshold triggering detection
133 */
134 public T getDistanceThreshold() {
135 return distanceThreshold;
136 }
137 }