AbstractOneWayGNSS.java
/* Copyright 2022-2026 RomainSerra
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
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*/
package org.orekit.estimation.measurements.gnss;
import java.util.Arrays;
import java.util.Collections;
import java.util.Map;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.analysis.differentiation.GradientField;
import org.orekit.estimation.measurements.AbstractMeasurement;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.MeasurementQuality;
import org.orekit.estimation.measurements.ObservableSatellite;
import org.orekit.estimation.measurements.ObservedMeasurement;
import org.orekit.estimation.measurements.Observer;
import org.orekit.estimation.measurements.SignalBasedMeasurement;
import org.orekit.frames.Frame;
import org.orekit.propagation.SpacecraftState;
import org.orekit.signal.AdjustableEmitterSignalTimer;
import org.orekit.signal.FieldAdjustableEmitterSignalTimer;
import org.orekit.signal.FieldSignalReceptionCondition;
import org.orekit.signal.SignalReceptionCondition;
import org.orekit.signal.SignalTravelTimeModel;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.time.clocks.ClockOffset;
import org.orekit.time.clocks.FieldClockOffset;
import org.orekit.time.clocks.QuadraticFieldClockModel;
import org.orekit.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.PVCoordinatesProvider;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.TimeSpanMap.Span;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinates;
/** Abstract class for one-way GNSS measurement.
* @author Romain Serra
* @since 14.0
*/
public abstract class AbstractOneWayGNSS<T extends ObservedMeasurement<T>> extends SignalBasedMeasurement<T> {
/** Observer sending measurement data. */
private final Observer observer;
/** Simple constructor.
* @param observer sender of GNSS signal
* @param date date of the measurement
* @param observedValue observed value
* @param measurementQuality measurement quality
* @param signalTravelTimeModel time delay computer
* @param local satellite which receives the signal and perform the measurement
*/
protected AbstractOneWayGNSS(final Observer observer, final AbsoluteDate date,
final double observedValue, final MeasurementQuality measurementQuality,
final SignalTravelTimeModel signalTravelTimeModel, final ObservableSatellite local) {
// Call super constructor
this(observer, date, new double[] { observedValue }, measurementQuality,
signalTravelTimeModel, local);
}
/** Simple constructor.
* @param observer sender of GNSS signal
* @param date date of the measurement
* @param observedValue observed value
* @param measurementQuality measurement quality
* @param signalTravelTimeModel time delay computer
* @param local satellite which receives the signal and perform the measurement
*/
protected AbstractOneWayGNSS(final Observer observer, final AbsoluteDate date,
final double[] observedValue, final MeasurementQuality measurementQuality,
final SignalTravelTimeModel signalTravelTimeModel, final ObservableSatellite local) {
// Call super constructor
super(date, false, observedValue, measurementQuality,
signalTravelTimeModel, Collections.singletonList(local));
this.observer = observer;
}
/** Observer object sending signal.
* @return observer object
*/
public final Observer getObserver() {
return observer;
}
/** Compute common estimation parameters in case where measured object is the
* receiver of the signal value (e.g. GNSS to ObservableSatellite).
* @param states state(s) of all measured spacecraft
* @param localSat satellite whose state is being estimated
* @param measurementDate date when measurement was taken
* by the receiver clock (i.e. clock offset <em>not</em> compensated), if false,
* the specified {@code date} was already compensated and is a physical absolute date
* @return common parameters
*/
CommonParametersWithoutDerivatives computeLocalParametersWithout(final SpacecraftState[] states,
final ObservableSatellite localSat,
final AbsoluteDate measurementDate) {
// Coordinates of the observed spacecraft
final Frame frame = states[0].getFrame();
final TimeStampedPVCoordinates pvaLocal = states[0].getPVCoordinates(frame);
// Clock values of the observed spacecraft and signal receiver
final ClockOffset localClock = localSat.getQuadraticClockModel().getOffset(measurementDate);
final double localClockBias = localClock.getBias();
// take clock bias of receiver (in this case, ObservableSatellite) into account
final AbsoluteDate arrivalDate = measurementDate.shiftedBy(-localClockBias);
// Coordinates provider of the Observer object providing the signal information
final PVCoordinatesProvider remotePV = getObserver().getPVCoordinatesProvider();
// Downlink delay / determine time-of-emission of signal information from remote object
final double deltaT = arrivalDate.durationFrom(states[0]);
final TimeStampedPVCoordinates pvaDownlink = pvaLocal.shiftedBy(deltaT);
final AdjustableEmitterSignalTimer signalTimeOfFlight = getSignalTravelTimeModel()
.getAdjustableEmitterComputer(remotePV);
final double tauD = signalTimeOfFlight.computeDelay(new SignalReceptionCondition(arrivalDate,
pvaDownlink.getPosition(), frame), arrivalDate);
// Remote object pos/vel at time of signal emission
final AbsoluteDate emissionDate = arrivalDate.shiftedBy(-tauD);
final ClockOffset remoteClock = getObserver().getQuadraticClockModel().getOffset(emissionDate);
return new CommonParametersWithoutDerivatives(states[0], tauD,
localClock, remoteClock,
states[0].shiftedBy(deltaT),
pvaDownlink,
remotePV.getPVCoordinates(emissionDate, frame));
}
/** Compute common estimation parameters with derivatives when the measured object is the
* receiver of the signal sent by the Observer.
* @param states state(s) of all measured spacecraft
* @param localSat satellite whose state is being estimated
* @param measurementDate date when measurement was taken
* @return common parameters
*/
CommonParametersWithDerivatives computeLocalParametersWith(final SpacecraftState[] states,
final ObservableSatellite localSat,
final AbsoluteDate measurementDate) {
// Create the parameter indices map
final Frame frame = states[0].getFrame();
final Map<String, Integer> paramIndices = getParameterIndices(states);
final int nbParams = 6 * states.length + paramIndices.size();
// Turn measurement date into FieldAbsoluteDate<Gradient>
final FieldAbsoluteDate<Gradient> gDate = new FieldAbsoluteDate<>(GradientField.getField(nbParams), measurementDate);
// Measured satellite object data
final TimeStampedFieldPVCoordinates<Gradient> pvaLocal = AbstractMeasurement.getCoordinates(states[0], 0, nbParams);
final QuadraticFieldClockModel<Gradient> localClock = localSat.getQuadraticClockModel().
toGradientModel(nbParams, paramIndices, measurementDate);
final FieldClockOffset<Gradient> localClockOffset = localClock.getOffset(gDate);
// take clock offset into account for arrival date
final FieldAbsoluteDate<Gradient> arrivalDate = gDate.shiftedBy(localClockOffset.getBias().negate());
// Coords provider for observer object that is sending signal
final FieldPVCoordinatesProvider<Gradient> remotePV = getObserver().getFieldPVCoordinatesProvider(nbParams, paramIndices);
// Downlink delay
final Gradient deltaT = arrivalDate.durationFrom(states[0].getDate());
final TimeStampedFieldPVCoordinates<Gradient> pvaDownlink = pvaLocal.shiftedBy(deltaT);
final FieldAdjustableEmitterSignalTimer<Gradient> fieldComputer = getSignalTravelTimeModel().
getFieldAdjustableEmitterComputer(arrivalDate.getField(), remotePV);
final FieldSignalReceptionCondition<Gradient> receptionCondition = new FieldSignalReceptionCondition<>(arrivalDate,
pvaDownlink.getPosition(), frame);
final Gradient tauD = fieldComputer.computeDelay(receptionCondition, arrivalDate);
// Remote observer at signal emission time
final FieldAbsoluteDate<Gradient> emissionDate = arrivalDate.shiftedBy(tauD.negate());
final QuadraticFieldClockModel<Gradient> remoteClock = getObserver().getQuadraticFieldClock(nbParams,
emissionDate.toAbsoluteDate(), paramIndices);
final FieldClockOffset<Gradient> remoteClockOffset = remoteClock.getOffset(emissionDate);
return new CommonParametersWithDerivatives(states[0], paramIndices, tauD,
localClockOffset, remoteClockOffset,
states[0].shiftedBy(deltaT.getValue()),
pvaDownlink,
remotePV.getPVCoordinates(emissionDate, frame));
}
/**
* Method filling estimated measurement.
* @param observedValue theoretical value with automatic differentiation
* @param indices mapping between parameter name and variable index
* @param estimated object to fill
*/
protected void fillDerivatives(final Gradient observedValue, final Map<String, Integer> indices,
final EstimatedMeasurement<T> estimated) {
final double[] derivatives = observedValue.getGradient();
// Set value and state first order derivatives of the estimated measurement
estimated.setEstimatedValue(observedValue.getValue());
estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));
// Set first order derivatives with respect to parameters
for (final ParameterDriver measurementDriver : getParametersDrivers()) {
for (Span<String> span = measurementDriver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
final Integer index = indices.get(span.getData());
if (index != null) {
estimated.setParameterDerivatives(measurementDriver, span.getStart(), derivatives[index]);
}
}
}
}
}