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.analytical.gnss;
18
19 import org.hipparchus.CalculusFieldElement;
20 import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
21 import org.hipparchus.util.MathArrays;
22 import org.orekit.propagation.FieldAdditionalDataProvider;
23 import org.orekit.propagation.FieldSpacecraftState;
24 import org.orekit.propagation.analytical.gnss.data.FieldGNSSClockElements;
25 import org.orekit.time.FieldAbsoluteDate;
26 import org.orekit.utils.Constants;
27 import org.orekit.utils.FieldPVCoordinates;
28
29 /** Provider for clock corrections as additional states.
30 * <p>
31 * The value of this additional state is a three elements array containing
32 * </p>
33 * <ul>
34 * <li>at index 0, the polynomial satellite clock model
35 * Δtₛₐₜ = {@link FieldGNSSClockElements#getAf0() a₀} +
36 * {@link FieldGNSSClockElements#getAf1() a₁} (t - {@link FieldGNSSClockElements#getToc() toc}) +
37 * {@link FieldGNSSClockElements#getAf1() a₂} (t - {@link FieldGNSSClockElements#getToc() toc})²
38 * </li>
39 * <li>at index 1 the relativistic clock correction due to eccentricity</li>
40 * <li>at index 2 the estimated group delay differential {@link FieldGNSSClockElements#getTGD() TGD} for L1-L2 correction</li>
41 * </ul>
42 *
43 * @param <T> type of the field elements
44 * @author Luc Maisonobe
45 * @since 13.0
46 */
47 public class FieldClockCorrectionsProvider<T extends CalculusFieldElement<T>>
48 implements FieldAdditionalDataProvider<T[], T> {
49
50 /** The GPS clock elements. */
51 private final FieldGNSSClockElements<T> gnssClk;
52
53 /** Clock reference epoch. */
54 private final FieldAbsoluteDate<T> clockRef;
55
56 /** Duration of the GNSS cycle in seconds. */
57 private final double cycleDuration;
58
59 /** Simple constructor.
60 * @param gnssClk GNSS clock elements
61 * @param cycleDuration duration of the GNSS cycle in seconds
62 */
63 public FieldClockCorrectionsProvider(final FieldGNSSClockElements<T> gnssClk,
64 final double cycleDuration) {
65 this.gnssClk = gnssClk;
66 this.clockRef = gnssClk.getDate();
67 this.cycleDuration = cycleDuration;
68 }
69
70 /** {@inheritDoc} */
71 @Override
72 public String getName() {
73 return ClockCorrectionsProvider.CLOCK_CORRECTIONS;
74 }
75
76 /**
77 * Get the duration from clock Reference epoch.
78 * <p>This takes the GNSS week roll-over into account.</p>
79 *
80 * @param date the considered date
81 * @return the duration from clock Reference epoch (s)
82 */
83 private T getDT(final FieldAbsoluteDate<T> date) {
84 // Time from ephemeris reference epoch
85 T dt = date.durationFrom(clockRef);
86 // Adjusts the time to take roll over week into account
87 while (dt.getReal() > 0.5 * cycleDuration) {
88 dt = dt.subtract(cycleDuration);
89 }
90 while (dt.getReal() < -0.5 * cycleDuration) {
91 dt = dt.add(cycleDuration);
92 }
93 // Returns the time from ephemeris reference epoch
94 return dt;
95 }
96
97 /** {@inheritDoc} */
98 @Override
99 public T[] getAdditionalData(final FieldSpacecraftState<T> state) {
100
101 // polynomial clock model
102 final T dt = getDT(state.getDate());
103 final T dtSat = gnssClk.getAf0().add(dt.multiply(gnssClk.getAf1().add(dt.multiply(gnssClk.getAf2()))));
104
105 // relativistic effect due to eccentricity
106 final FieldPVCoordinates<T> pv = state.getPVCoordinates();
107 final T dtRel = FieldVector3D.dotProduct(pv.getPosition(), pv.getVelocity()).
108 multiply(-2 / (Constants.SPEED_OF_LIGHT * Constants.SPEED_OF_LIGHT));
109
110 // estimated group delay differential
111 final T tg = gnssClk.getTGD();
112
113 final T[] array = MathArrays.buildArray(dt.getField(), 3);
114 array[0] = dtSat;
115 array[1] = dtRel;
116 array[2] = tg;
117 return array;
118 }
119
120 }