1 /* Copyright 2022-2025 Luc Maisonobe
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.propagation.events;
18
19 import org.hipparchus.CalculusFieldElement;
20 import org.hipparchus.Field;
21 import org.hipparchus.analysis.differentiation.FieldUnivariateDerivative1;
22 import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
23 import org.hipparchus.ode.events.FieldEventSlopeFilter;
24 import org.orekit.frames.FieldStaticTransform;
25 import org.orekit.frames.TopocentricFrame;
26 import org.orekit.propagation.FieldSpacecraftState;
27 import org.orekit.propagation.events.handlers.FieldEventHandler;
28 import org.orekit.propagation.events.handlers.FieldStopOnIncreasing;
29
30 /** Detector for elevation extremum with respect to a ground point.
31 * <p>This detector identifies when a spacecraft reaches its
32 * extremum elevation with respect to a ground point.</p>
33 * <p>
34 * As in most cases only the elevation maximum is needed and the
35 * minimum is often irrelevant, this detector is often wrapped into
36 * an {@link FieldEventSlopeFilter event slope filter} configured with
37 * {@link FilterType#TRIGGER_ONLY_DECREASING_EVENTS} (i.e. when the
38 * elevation derivative decreases from positive values to negative values,
39 * which correspond to a maximum). Setting up this filter saves some computation
40 * time as the elevation minimum occurrences are not even looked at. It is
41 * however still often necessary to do an additional filtering
42 * </p>
43 * @param <T> type of the field element
44 * @author Luc Maisonobe
45 * @since 12.0
46 */
47 public class FieldElevationExtremumDetector<T extends CalculusFieldElement<T>>
48 extends FieldAbstractTopocentricDetector<FieldElevationExtremumDetector<T>, T> {
49
50 /** Build a new detector.
51 * <p>The new instance uses default values for maximal checking interval
52 * ({@link #DEFAULT_MAX_CHECK}) and convergence threshold ({@link
53 * #DEFAULT_THRESHOLD}).</p>
54 * @param field field to which elements belong
55 * @param topo topocentric frame centered on ground point
56 */
57 public FieldElevationExtremumDetector(final Field<T> field, final TopocentricFrame topo) {
58 this(field.getZero().newInstance(DEFAULT_MAX_CHECK),
59 field.getZero().newInstance(DEFAULT_THRESHOLD),
60 topo);
61 }
62
63 /** Build a detector.
64 * @param maxCheck maximal checking interval (s)
65 * @param threshold convergence threshold (s)
66 * @param topo topocentric frame centered on ground point
67 */
68 public FieldElevationExtremumDetector(final T maxCheck, final T threshold,
69 final TopocentricFrame topo) {
70 this(new FieldEventDetectionSettings<>(maxCheck.getReal(), threshold, DEFAULT_MAX_ITER), new FieldStopOnIncreasing<>(),
71 topo);
72 }
73
74 /** Protected constructor with full parameters.
75 * <p>
76 * This constructor is not public as users are expected to use the builder
77 * API with the various {@code withXxx()} methods to set up the instance
78 * in a readable manner without using a huge amount of parameters.
79 * </p>
80 * @param detectionSettings event detection settings
81 * @param handler event handler to call at event occurrences
82 * @param topo topocentric frame centered on ground point
83 */
84 protected FieldElevationExtremumDetector(final FieldEventDetectionSettings<T> detectionSettings,
85 final FieldEventHandler<T> handler,
86 final TopocentricFrame topo) {
87 super(detectionSettings, handler, topo);
88 }
89
90 /** {@inheritDoc} */
91 @Override
92 protected FieldElevationExtremumDetector<T> create(final FieldEventDetectionSettings<T> detectionSettings,
93 final FieldEventHandler<T> newHandler) {
94 return new FieldElevationExtremumDetector<>(detectionSettings, newHandler, getTopocentricFrame());
95 }
96
97 /** Get the elevation value.
98 * @param s the current state information: date, kinematics, attitude
99 * @return spacecraft elevation
100 */
101 public T getElevation(final FieldSpacecraftState<T> s) {
102 return getTopocentricFrame().getElevation(s.getPosition(), s.getFrame(), s.getDate());
103 }
104
105 /** Compute the value of the detection function.
106 * <p>
107 * The value is the spacecraft elevation first time derivative.
108 * </p>
109 * @param s the current state information: date, kinematics, attitude
110 * @return spacecraft elevation first time derivative
111 */
112 public T g(final FieldSpacecraftState<T> s) {
113
114 // get position, velocity acceleration of spacecraft in topocentric frame
115 final FieldStaticTransform<FieldUnivariateDerivative1<T>> inertToTopo = s.getFrame().getStaticTransformTo(getTopocentricFrame(),
116 s.getDate().toFUD1Field());
117 final FieldVector3D<FieldUnivariateDerivative1<T>> positionInert = s.getPVCoordinates().toUnivariateDerivative1Vector();
118 final FieldVector3D<FieldUnivariateDerivative1<T>> posTopo = inertToTopo.transformPosition(positionInert);
119
120 // compute elevation and its first time derivative
121 final FieldUnivariateDerivative1<T> elevation = posTopo.getDelta();
122
123 // return elevation first time derivative
124 return elevation.getFirstDerivative();
125
126 }
127
128 }