1 /* Copyright 2002-2025 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.geometry.euclidean.threed.FieldVector3D;
21 import org.orekit.frames.Frame;
22 import org.orekit.frames.TopocentricFrame;
23 import org.orekit.models.AtmosphericRefractionModel;
24 import org.orekit.propagation.FieldSpacecraftState;
25 import org.orekit.propagation.events.handlers.FieldContinueOnEvent;
26 import org.orekit.propagation.events.handlers.FieldEventHandler;
27 import org.orekit.time.FieldAbsoluteDate;
28 import org.orekit.utils.ExtendedPositionProvider;
29
30
31 /** Detector for ground location being at night.
32 * <p>
33 * This detector is mainly useful for scheduling optical measurements
34 * (either passive telescope observation of satellites against the stars background
35 * or active satellite laser ranging).
36 * </p>
37 * <p>
38 * The {@code g} function of this detector is positive when ground is at night
39 * (i.e. Sun is below dawn/dusk elevation angle).
40 * </p>
41 * @author Luc Maisonobe
42 * @author Romain Serra
43 * @see GroundAtNightDetector
44 * @since 13.1
45 */
46 public class FieldGroundAtNightDetector<T extends CalculusFieldElement<T>>
47 extends FieldAbstractTopocentricDetector<FieldGroundAtNightDetector<T>, T> {
48
49 /** Provider for Sun position. */
50 private final ExtendedPositionProvider sun;
51
52 /** Sun elevation below which we consider night is dark enough. */
53 private final T dawnDuskElevation;
54
55 /** Atmospheric Model used for calculations, if defined. */
56 private final AtmosphericRefractionModel refractionModel;
57
58 /** Simple constructor.
59 * @param topocentricFrame ground location to check
60 * @param sun provider for Sun position
61 * @param dawnDuskElevation Sun elevation below which we consider night is dark enough (rad)
62 * @param refractionModel reference to refraction model (null if refraction should be ignored)
63 */
64 public FieldGroundAtNightDetector(final TopocentricFrame topocentricFrame, final ExtendedPositionProvider sun,
65 final T dawnDuskElevation,
66 final AtmosphericRefractionModel refractionModel) {
67 this(topocentricFrame, sun, dawnDuskElevation, refractionModel, new FieldEventDetectionSettings<>(dawnDuskElevation.getField(),
68 EventDetectionSettings.getDefaultEventDetectionSettings()), new FieldContinueOnEvent<>());
69 }
70
71 /** Private constructor.
72 * @param topocentricFrame ground location from which measurement is performed
73 * @param sun provider for Sun position
74 * @param dawnDuskElevation Sun elevation below which we consider night is dark enough (rad)
75 * @param refractionModel reference to refraction model (null if refraction should be ignored),
76 * @param detectionSettings event detection settings
77 * @param handler event handler to call at event occurrences
78 */
79 protected FieldGroundAtNightDetector(final TopocentricFrame topocentricFrame, final ExtendedPositionProvider sun,
80 final T dawnDuskElevation,
81 final AtmosphericRefractionModel refractionModel,
82 final FieldEventDetectionSettings<T> detectionSettings,
83 final FieldEventHandler<T> handler) {
84 super(detectionSettings, handler, topocentricFrame);
85 this.sun = sun;
86 this.dawnDuskElevation = dawnDuskElevation;
87 this.refractionModel = refractionModel;
88 }
89
90 /** {@inheritDoc} */
91 @Override
92 protected FieldGroundAtNightDetector<T> create(final FieldEventDetectionSettings<T> detectionSettings,
93 final FieldEventHandler<T> newHandler) {
94 return new FieldGroundAtNightDetector<>(getTopocentricFrame(), sun, dawnDuskElevation, refractionModel,
95 detectionSettings, newHandler);
96 }
97
98 @Override
99 public boolean dependsOnTimeOnly() {
100 return true;
101 }
102
103 /** {@inheritDoc}
104 * <p>
105 * The {@code g} function of this detector is positive when ground is at night
106 * (i.e. Sun is below dawn/dusk elevation angle).
107 * </p>
108 * <p>
109 * This function only depends on date, not on the actual position of the spacecraft.
110 * </p>
111 */
112 @Override
113 public T g(final FieldSpacecraftState<T> state) {
114
115 final FieldAbsoluteDate<T> date = state.getDate();
116 final Frame frame = state.getFrame();
117 final FieldVector3D<T> position = sun.getPosition(date, frame);
118 final T trueElevation = getTopocentricFrame().getElevation(position, frame, date);
119
120 final T calculatedElevation;
121 if (refractionModel != null) {
122 calculatedElevation = trueElevation.add(refractionModel.getRefraction(trueElevation.getReal()));
123 } else {
124 calculatedElevation = trueElevation;
125 }
126
127 return dawnDuskElevation.subtract(calculatedElevation);
128
129 }
130
131 }