1 /* Copyright 2002-2024 CS GROUP
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.ode.events.Action;
21 import org.hipparchus.util.FastMath;
22 import org.hipparchus.util.MathUtils;
23 import org.orekit.frames.Frame;
24 import org.orekit.orbits.FieldOrbit;
25 import org.orekit.orbits.KeplerianOrbit;
26 import org.orekit.orbits.Orbit;
27 import org.orekit.orbits.OrbitType;
28 import org.orekit.orbits.PositionAngleType;
29 import org.orekit.propagation.FieldSpacecraftState;
30 import org.orekit.propagation.events.handlers.FieldEventHandler;
31 import org.orekit.propagation.events.handlers.FieldStopOnIncreasing;
32
33 /** Finder for node crossing events.
34 * <p>This class finds equator crossing events (i.e. ascending
35 * or descending node crossing).</p>
36 * <p>The default implementation behavior is to {@link Action#CONTINUE continue}
37 * propagation at descending node crossing and to {@link Action#STOP stop} propagation
38 * at ascending node crossing. This can be changed by calling
39 * {@link #withHandler(FieldEventHandler)} after construction.</p>
40 * <p>Beware that node detection will fail for almost equatorial orbits. If
41 * for example a node detector is used to trigger an {@link
42 * org.orekit.forces.maneuvers.ImpulseManeuver ImpulseManeuver} and the maneuver
43 * turn the orbit plane to equator, then the detector may completely fail just
44 * after the maneuver has been performed! This is a real case that has been
45 * encountered during validation ...</p>
46 * @see org.orekit.propagation.FieldPropagator#addEventDetector(FieldEventDetector)
47 * @author Luc Maisonobe
48 * @param <T> type of the field elements
49 */
50 public class FieldNodeDetector<T extends CalculusFieldElement<T>> extends FieldAbstractDetector<FieldNodeDetector<T>, T> {
51
52 /** Frame in which the equator is defined. */
53 private final Frame frame;
54
55 /** Build a new instance.
56 * <p>The orbit is used only to set an upper bound for the max check interval
57 * to period/3 and to set the convergence threshold according to orbit size.</p>
58 * @param orbit initial orbit
59 * @param frame frame in which the equator is defined (typical
60 * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
61 * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
62 */
63 public FieldNodeDetector(final FieldOrbit<T> orbit, final Frame frame) {
64 this(orbit.getKeplerianPeriod().multiply(1.0e-13), orbit, frame);
65 }
66
67 /** Build a new instance.
68 * <p>The orbit is used only to set an upper bound for the max check interval
69 * to period/3.</p>
70 * @param threshold convergence threshold (s)
71 * @param orbit initial orbit
72 * @param frame frame in which the equator is defined (typical
73 * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
74 * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
75 */
76 public FieldNodeDetector(final T threshold, final FieldOrbit<T> orbit, final Frame frame) {
77 this(FieldAdaptableInterval.of(orbit.getA().getField().getZero().newInstance(2 * estimateNodesTimeSeparation(orbit.toOrbit()) / 3).getReal()),
78 threshold, DEFAULT_MAX_ITER, new FieldStopOnIncreasing<>(), frame);
79 }
80
81 /** Protected constructor with full parameters.
82 * <p>
83 * This constructor is not public as users are expected to use the builder
84 * API with the various {@code withXxx()} methods to set up the instance
85 * in a readable manner without using a huge amount of parameters.
86 * </p>
87 * @param maxCheck maximum checking interval
88 * @param threshold convergence threshold (s)
89 * @param maxIter maximum number of iterations in the event time search
90 * @param handler event handler to call at event occurrences
91 * @param frame frame in which the equator is defined (typical
92 * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
93 * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
94 * @since 6.1
95 */
96 protected FieldNodeDetector(final FieldAdaptableInterval<T> maxCheck, final T threshold,
97 final int maxIter, final FieldEventHandler<T> handler,
98 final Frame frame) {
99 super(maxCheck, threshold, maxIter, handler);
100 this.frame = frame;
101 }
102
103 /** {@inheritDoc} */
104 @Override
105 protected FieldNodeDetector<T> create(final FieldAdaptableInterval<T> newMaxCheck, final T newThreshold,
106 final int newMaxIter, final FieldEventHandler<T> newHandler) {
107 return new FieldNodeDetector<>(newMaxCheck, newThreshold, newMaxIter, newHandler, frame);
108 }
109
110 /** Find time separation between nodes.
111 * <p>
112 * The estimation of time separation is based on Keplerian motion, it is only
113 * used as a rough guess for a safe setting of default max check interval for
114 * event detection.
115 * </p>
116 * @param orbit initial orbit
117 * @return minimum time separation between nodes
118 */
119 private static double estimateNodesTimeSeparation(final Orbit orbit) {
120
121 final KeplerianOrbit keplerian = (KeplerianOrbit) OrbitType.KEPLERIAN.convertType(orbit);
122
123 // mean anomaly of ascending node
124 final double ascendingM = new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
125 keplerian.getI(),
126 keplerian.getPerigeeArgument(),
127 keplerian.getRightAscensionOfAscendingNode(),
128 -keplerian.getPerigeeArgument(), PositionAngleType.TRUE,
129 keplerian.getFrame(), keplerian.getDate(),
130 keplerian.getMu()).getMeanAnomaly();
131
132 // mean anomaly of descending node
133 final double descendingM = new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
134 keplerian.getI(),
135 keplerian.getPerigeeArgument(),
136 keplerian.getRightAscensionOfAscendingNode(),
137 FastMath.PI - keplerian.getPerigeeArgument(), PositionAngleType.TRUE,
138 keplerian.getFrame(), keplerian.getDate(),
139 keplerian.getMu()).getMeanAnomaly();
140
141 // differences between mean anomalies
142 final double delta1 = MathUtils.normalizeAngle(ascendingM, descendingM + FastMath.PI) - descendingM;
143 final double delta2 = 2 * FastMath.PI - delta1;
144
145 // minimum time separation between the two nodes
146 return FastMath.min(delta1, delta2) / keplerian.getKeplerianMeanMotion();
147
148 }
149
150 /** Get the frame in which the equator is defined.
151 * @return the frame in which the equator is defined
152 */
153 public Frame getFrame() {
154 return frame;
155 }
156
157 /** Compute the value of the switching function.
158 * This function computes the Z position in the defined frame.
159 * @param s the current state information: date, kinematics, attitude
160 * @return value of the switching function
161 */
162 public T g(final FieldSpacecraftState<T> s) {
163 return s.getPosition(frame).getZ();
164 }
165
166 // public NodeDetector toNoField() {
167 // return new NodeDetector(getThreshold().getReal(), orbit.toOrbit(), frame);
168 // }
169
170 }