1 /* Copyright 2002-2019 CS Systèmes d'Information
2 * Licensed to CS Systèmes d'Information (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.estimation.measurements;
18
19 import java.util.Arrays;
20 import java.util.HashMap;
21 import java.util.Map;
22
23 import org.hipparchus.Field;
24 import org.hipparchus.analysis.differentiation.DSFactory;
25 import org.hipparchus.analysis.differentiation.DerivativeStructure;
26 import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
27 import org.orekit.frames.FieldTransform;
28 import org.orekit.propagation.SpacecraftState;
29 import org.orekit.time.AbsoluteDate;
30 import org.orekit.time.FieldAbsoluteDate;
31 import org.orekit.utils.Constants;
32 import org.orekit.utils.ParameterDriver;
33 import org.orekit.utils.TimeStampedFieldPVCoordinates;
34 import org.orekit.utils.TimeStampedPVCoordinates;
35
36 /** Class modeling a range measurement from a ground station.
37 * <p>
38 * For one-way measurements, a signal is emitted by the satellite
39 * and received by the ground station. The measurement value is the
40 * elapsed time between emission and reception multiplied by c where
41 * c is the speed of light.
42 * </p>
43 * <p>
44 * For two-way measurements, the measurement is considered to be a signal
45 * emitted from a ground station, reflected on spacecraft, and received
46 * on the same ground station. Its value is the elapsed time between
47 * emission and reception multiplied by c/2 where c is the speed of light.
48 * </p>
49 * <p>
50 * The motion of both the station and the spacecraft during the signal
51 * flight time are taken into account. The date of the measurement
52 * corresponds to the reception on ground of the emitted or reflected signal.
53 * </p>
54 * <p>
55 * The clock offsets of both the ground station and the satellite are taken
56 * into account. These offsets correspond to the values that must be subtracted
57 * from station (resp. satellite) reading of time to compute the real physical
58 * date. These offsets have two effects:
59 * </p>
60 * <ul>
61 * <li>as measurement date is evaluated at reception time, the real physical date
62 * of the measurement is the observed date to which the receiving ground station
63 * clock offset is subtracted</li>
64 * <li>as range is evaluated using the total signal time of flight, for one-way
65 * measurements the observed range is the real physical signal time of flight to
66 * which (Δtg - Δts) ⨉ c is added, where Δtg (resp. Δts) is the clock offset for the
67 * receiving ground station (resp. emitting satellite). A similar effect exists in
68 * two-way measurements but it is computed as (Δtg - Δtg) ⨉ c / 2 as the same ground
69 * station clock is used for initial emission and final reception and therefore it evaluates
70 * to zero.</li>
71 * </ul>
72 * <p>
73 * @author Thierry Ceolin
74 * @author Luc Maisonobe
75 * @author Maxime Journot
76 * @since 8.0
77 */
78 public class Range extends AbstractMeasurement<Range> {
79
80 /** Ground station from which measurement is performed. */
81 private final GroundStation station;
82
83 /** Flag indicating whether it is a two-way measurement. */
84 private final boolean twoway;
85
86 /** Simple constructor.
87 * <p>
88 * This constructor uses 0 as the index of the propagator related
89 * to this measurement, thus being well suited for mono-satellite
90 * orbit determination.
91 * </p>
92 * @param station ground station from which measurement is performed
93 * @param date date of the measurement
94 * @param range observed value
95 * @param sigma theoretical standard deviation
96 * @param baseWeight base weight
97 * @deprecated as of 9.3, replaced by {@link #Range(GroundStation, boolean, AbsoluteDate,
98 * double, double, double, ObservableSatellite)}
99 */
100 @Deprecated
101 public Range(final GroundStation station, final AbsoluteDate date,
102 final double range, final double sigma, final double baseWeight) {
103 this(station, true, date, range, sigma, baseWeight, new ObservableSatellite(0));
104 }
105
106 /** Simple constructor.
107 * <p>
108 * This constructor uses 0 as the index of the propagator related
109 * to this measurement, thus being well suited for mono-satellite
110 * orbit determination.
111 * </p>
112 * @param station ground station from which measurement is performed
113 * @param date date of the measurement
114 * @param range observed value
115 * @param sigma theoretical standard deviation
116 * @param baseWeight base weight
117 * @param twoWay flag indicating whether it is a two-way measurement
118 * @deprecated as of 9.3, replaced by {@link #Range(GroundStation, boolean, AbsoluteDate,
119 * double, double, double, ObservableSatellite)}
120 */
121 @Deprecated
122 public Range(final GroundStation station, final AbsoluteDate date, final double range,
123 final double sigma, final double baseWeight, final boolean twoWay) {
124 this(station, twoWay, date, range, sigma, baseWeight, new ObservableSatellite(0));
125 }
126
127 /** Simple constructor.
128 * @param station ground station from which measurement is performed
129 * @param date date of the measurement
130 * @param range observed value
131 * @param sigma theoretical standard deviation
132 * @param baseWeight base weight
133 * @param propagatorIndex index of the propagator related to this measurement
134 * @deprecated as of 9.3, replaced by {@link #Range(GroundStation, boolean, AbsoluteDate,
135 * double, double, double, ObservableSatellite)}
136 */
137 @Deprecated
138 public Range(final GroundStation station, final AbsoluteDate date,
139 final double range, final double sigma, final double baseWeight,
140 final int propagatorIndex) {
141 this(station, true, date, range, sigma, baseWeight, new ObservableSatellite(0));
142 }
143
144 /** Simple constructor.
145 * @param station ground station from which measurement is performed
146 * @param twoWay flag indicating whether it is a two-way measurement
147 * @param date date of the measurement
148 * @param range observed value
149 * @param sigma theoretical standard deviation
150 * @param baseWeight base weight
151 * @param propagatorIndex index of the propagator related to this measurement
152 * @since 9.0
153 * @deprecated as of 9.3, replaced by {@link #Range(GroundStation, boolean, AbsoluteDate,
154 * double, double, double, ObservableSatellite)}
155 */
156 @Deprecated
157 public Range(final GroundStation station, final boolean twoWay, final AbsoluteDate date,
158 final double range, final double sigma, final double baseWeight,
159 final int propagatorIndex) {
160 this(station, twoWay, date, range, sigma, baseWeight, new ObservableSatellite(propagatorIndex));
161 }
162
163 /** Simple constructor.
164 * @param station ground station from which measurement is performed
165 * @param twoWay flag indicating whether it is a two-way measurement
166 * @param date date of the measurement
167 * @param range observed value
168 * @param sigma theoretical standard deviation
169 * @param baseWeight base weight
170 * @param satellite satellite related to this measurement
171 * @since 9.3
172 */
173 public Range(final GroundStation station, final boolean twoWay, final AbsoluteDate date,
174 final double range, final double sigma, final double baseWeight,
175 final ObservableSatellite satellite) {
176 super(date, range, sigma, baseWeight, Arrays.asList(satellite));
177 addParameterDriver(station.getClockOffsetDriver());
178 addParameterDriver(station.getEastOffsetDriver());
179 addParameterDriver(station.getNorthOffsetDriver());
180 addParameterDriver(station.getZenithOffsetDriver());
181 addParameterDriver(station.getPrimeMeridianOffsetDriver());
182 addParameterDriver(station.getPrimeMeridianDriftDriver());
183 addParameterDriver(station.getPolarOffsetXDriver());
184 addParameterDriver(station.getPolarDriftXDriver());
185 addParameterDriver(station.getPolarOffsetYDriver());
186 addParameterDriver(station.getPolarDriftYDriver());
187 if (!twoWay) {
188 // for one way measurements, the satellite clock offset affects the measurement
189 addParameterDriver(satellite.getClockOffsetDriver());
190 }
191 this.station = station;
192 this.twoway = twoWay;
193 }
194
195 /** Get the ground station from which measurement is performed.
196 * @return ground station from which measurement is performed
197 */
198 public GroundStation getStation() {
199 return station;
200 }
201
202 /** Check if the instance represents a two-way measurement.
203 * @return true if the instance represents a two-way measurement
204 */
205 public boolean isTwoWay() {
206 return twoway;
207 }
208
209 /** {@inheritDoc} */
210 @Override
211 protected EstimatedMeasurement<Range> theoreticalEvaluation(final int iteration,
212 final int evaluation,
213 final SpacecraftState[] states) {
214
215 final ObservableSatellite satellite = getSatellites().get(0);
216 final SpacecraftState state = states[satellite.getPropagatorIndex()];
217
218 // Range derivatives are computed with respect to spacecraft state in inertial frame
219 // and station parameters
220 // ----------------------
221 //
222 // Parameters:
223 // - 0..2 - Position of the spacecraft in inertial frame
224 // - 3..5 - Velocity of the spacecraft in inertial frame
225 // - 6..n - measurements parameters (clock offset, station offsets, pole, prime meridian, sat clock offset...)
226 int nbParams = 6;
227 final Map<String, Integer> indices = new HashMap<>();
228 for (ParameterDriver driver : getParametersDrivers()) {
229 if (driver.isSelected()) {
230 indices.put(driver.getName(), nbParams++);
231 }
232 }
233 final DSFactory factory = new DSFactory(nbParams, 1);
234 final Field<DerivativeStructure> field = factory.getDerivativeField();
235 final FieldVector3D<DerivativeStructure> zero = FieldVector3D.getZero(field);
236
237 // Coordinates of the spacecraft expressed as a derivative structure
238 final TimeStampedFieldPVCoordinates<DerivativeStructure> pvaDS = getCoordinates(state, 0, factory);
239
240 // transform between station and inertial frame, expressed as a derivative structure
241 // The components of station's position in offset frame are the 3 last derivative parameters
242 final FieldTransform<DerivativeStructure> offsetToInertialDownlink =
243 station.getOffsetToInertial(state.getFrame(), getDate(), factory, indices);
244 final FieldAbsoluteDate<DerivativeStructure> downlinkDateDS = offsetToInertialDownlink.getFieldDate();
245
246 // Station position in inertial frame at end of the downlink leg
247 final TimeStampedFieldPVCoordinates<DerivativeStructure> stationDownlink =
248 offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
249 zero, zero, zero));
250
251 // Compute propagation times
252 // (if state has already been set up to pre-compensate propagation delay,
253 // we will have delta == tauD and transitState will be the same as state)
254
255 // Downlink delay
256 final DerivativeStructure tauD = signalTimeOfFlight(pvaDS, stationDownlink.getPosition(), downlinkDateDS);
257
258 // Transit state & Transit state (re)computed with derivative structures
259 final DerivativeStructure delta = downlinkDateDS.durationFrom(state.getDate());
260 final DerivativeStructure deltaMTauD = tauD.negate().add(delta);
261 final SpacecraftState transitState = state.shiftedBy(deltaMTauD.getValue());
262 final TimeStampedFieldPVCoordinates<DerivativeStructure> transitStateDS = pvaDS.shiftedBy(deltaMTauD);
263
264 // prepare the evaluation
265 final EstimatedMeasurement<Range> estimated;
266 final DerivativeStructure range;
267
268 if (twoway) {
269
270 // Station at transit state date (derivatives of tauD taken into account)
271 final TimeStampedFieldPVCoordinates<DerivativeStructure> stationAtTransitDate =
272 stationDownlink.shiftedBy(tauD.negate());
273 // Uplink delay
274 final DerivativeStructure tauU =
275 signalTimeOfFlight(stationAtTransitDate, transitStateDS.getPosition(), transitStateDS.getDate());
276 final TimeStampedFieldPVCoordinates<DerivativeStructure> stationUplink =
277 stationDownlink.shiftedBy(-tauD.getValue() - tauU.getValue());
278
279 // Prepare the evaluation
280 estimated = new EstimatedMeasurement<Range>(this, iteration, evaluation,
281 new SpacecraftState[] {
282 transitState
283 }, new TimeStampedPVCoordinates[] {
284 stationUplink.toTimeStampedPVCoordinates(),
285 transitStateDS.toTimeStampedPVCoordinates(),
286 stationDownlink.toTimeStampedPVCoordinates()
287 });
288
289 // Range value
290 final double cOver2 = 0.5 * Constants.SPEED_OF_LIGHT;
291 final DerivativeStructure tau = tauD.add(tauU);
292 range = tau.multiply(cOver2);
293
294 } else {
295
296 estimated = new EstimatedMeasurement<Range>(this, iteration, evaluation,
297 new SpacecraftState[] {
298 transitState
299 }, new TimeStampedPVCoordinates[] {
300 transitStateDS.toTimeStampedPVCoordinates(),
301 stationDownlink.toTimeStampedPVCoordinates()
302 });
303
304 // Clock offsets
305 final DerivativeStructure dtg = station.getClockOffsetDriver().getValue(factory, indices);
306 final DerivativeStructure dts = satellite.getClockOffsetDriver().getValue(factory, indices);
307
308 // Range value
309 range = tauD.add(dtg).subtract(dts).multiply(Constants.SPEED_OF_LIGHT);
310
311 }
312
313 estimated.setEstimatedValue(range.getValue());
314
315 // Range partial derivatives with respect to state
316 final double[] derivatives = range.getAllDerivatives();
317 estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 1, 7));
318
319 // set partial derivatives with respect to parameters
320 // (beware element at index 0 is the value, not a derivative)
321 for (final ParameterDriver driver : getParametersDrivers()) {
322 final Integer index = indices.get(driver.getName());
323 if (index != null) {
324 estimated.setParameterDerivatives(driver, derivatives[index + 1]);
325 }
326 }
327
328 return estimated;
329
330 }
331
332 }