AbstractOnBoardMeasurement.java
/* Copyright 2002-2024 Luc Maisonobe
* 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
* limitations under the License.
*/
package org.orekit.estimation.measurements.gnss;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.analysis.differentiation.GradientField;
import org.orekit.estimation.measurements.AbstractMeasurement;
import org.orekit.estimation.measurements.ObservableSatellite;
import org.orekit.estimation.measurements.ObservedMeasurement;
import org.orekit.estimation.measurements.QuadraticClockModel;
import org.orekit.estimation.measurements.QuadraticFieldClockModel;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.ClockOffset;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.time.FieldClockOffset;
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;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/** Base class modeling a measurement where receiver is a satellite.
* @param <T> type of the measurement
* @author Luc Maisonobe
* @since 12.1
*/
public abstract class AbstractOnBoardMeasurement<T extends ObservedMeasurement<T>> extends AbstractMeasurement<T> {
/** Constructor.
* @param date date of the measurement
* @param observed observed value
* @param sigma theoretical standard deviation
* @param baseWeight base weight
* @param satellites satellites related to this measurement
*/
public AbstractOnBoardMeasurement(final AbsoluteDate date, final double observed,
final double sigma, final double baseWeight,
final List<ObservableSatellite> satellites) {
// Call to super constructor
super(date, observed, sigma, baseWeight, satellites);
// Add parameter drivers
satellites.forEach(s -> {
addParameterDriver(s.getClockOffsetDriver());
addParameterDriver(s.getClockDriftDriver());
addParameterDriver(s.getClockAccelerationDriver());
});
}
/** Get emitting satellite clock provider.
* @return emitting satellite clock provider
*/
protected abstract QuadraticClockModel getRemoteClock();
/** Get emitting satellite position/velocity provider.
* @param states states of all spacecraft involved in the measurement
* @return emitting satellite position/velocity provider
*/
protected abstract PVCoordinatesProvider getRemotePV(SpacecraftState[] states);
/** Get emitting satellite position/velocity provider.
* @param states states of all spacecraft involved in the measurement
* @param freeParameters total number of free parameters in the gradient
* @return emitting satellite position/velocity provider
*/
protected abstract FieldPVCoordinatesProvider<Gradient> getRemotePV(SpacecraftState[] states,
int freeParameters);
/** Get emitting satellite clock provider.
* @param freeParameters total number of free parameters in the gradient
* @param indices indices of the differentiation parameters in derivatives computations,
* must be span name and not driver name
* @return emitting satellite clock provider
*/
protected QuadraticFieldClockModel<Gradient> getRemoteClock(final int freeParameters,
final Map<String, Integer> indices) {
return getRemoteClock().toGradientModel(freeParameters, indices, getDate());
}
/** Compute common estimation parameters.
* @param states states of all spacecraft involved in the measurement
* @param clockOffsetAlreadyApplied if true, the specified {@code date} is as read
* 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
*/
protected OnBoardCommonParametersWithoutDerivatives computeCommonParametersWithout(final SpacecraftState[] states,
final boolean clockOffsetAlreadyApplied) {
// local and remote satellites
final TimeStampedPVCoordinates pvaLocal = states[0].getPVCoordinates();
final ClockOffset localClock = getSatellites().
get(0).
getQuadraticClockModel().
getOffset(getDate());
final double localClockOffset = localClock.getOffset();
final double localClockRate = localClock.getRate();
final PVCoordinatesProvider remotePV = getRemotePV(states);
// take clock offset into account
final AbsoluteDate arrivalDate = clockOffsetAlreadyApplied ? getDate() : getDate().shiftedBy(-localClockOffset);
// Downlink delay
final double deltaT = arrivalDate.durationFrom(states[0]);
final TimeStampedPVCoordinates pvaDownlink = pvaLocal.shiftedBy(deltaT);
final double tauD = signalTimeOfFlight(remotePV, arrivalDate, pvaDownlink.getPosition(),
arrivalDate, states[0].getFrame());
// Remote satellite at signal emission
final AbsoluteDate emissionDate = arrivalDate.shiftedBy(-tauD);
final ClockOffset remoteClock = getRemoteClock().getOffset(emissionDate);
final double remoteClockOffset = remoteClock.getOffset();
final double remoteClockRate = remoteClock.getRate();
return new OnBoardCommonParametersWithoutDerivatives(states[0],
localClockOffset, localClockRate,
remoteClockOffset, remoteClockRate,
tauD, pvaDownlink,
remotePV.getPVCoordinates(emissionDate, states[0].getFrame()));
}
/** Compute common estimation parameters.
* @param states states of all spacecraft involved in the measurement
* @param clockOffsetAlreadyApplied if true, the specified {@code date} is as read
* 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
*/
protected OnBoardCommonParametersWithDerivatives computeCommonParametersWith(final SpacecraftState[] states,
final boolean clockOffsetAlreadyApplied) {
// measurement derivatives are computed with respect to spacecraft state in inertial frame
// Parameters:
// - 6k..6k+2 - Position of spacecraft k (counting k from 0 to nbSat-1) in inertial frame
// - 6k+3..6k+5 - Velocity of spacecraft k (counting k from 0 to nbSat-1) in inertial frame
// - 6nbSat..n - measurements parameters (clock offset, etc)
int nbEstimatedParams = 6 * states.length;
final Map<String, Integer> parameterIndices = new HashMap<>();
for (ParameterDriver measurementDriver : getParametersDrivers()) {
if (measurementDriver.isSelected()) {
for (Span<String> span = measurementDriver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
parameterIndices.put(span.getData(), nbEstimatedParams++);
}
}
}
final FieldAbsoluteDate<Gradient> gDate = new FieldAbsoluteDate<>(GradientField.getField(nbEstimatedParams),
getDate());
// local and remote satellites
final TimeStampedFieldPVCoordinates<Gradient> pvaLocal = getCoordinates(states[0], 0, nbEstimatedParams);
final QuadraticFieldClockModel<Gradient> localClock = getSatellites().get(0).getQuadraticClockModel().
toGradientModel(nbEstimatedParams, parameterIndices, getDate());
final FieldClockOffset<Gradient> localClockOffset = localClock.getOffset(gDate);
final FieldPVCoordinatesProvider<Gradient> remotePV = getRemotePV(states, nbEstimatedParams);
// take clock offset into account
final FieldAbsoluteDate<Gradient> arrivalDate = clockOffsetAlreadyApplied ?
gDate : gDate.shiftedBy(localClockOffset.getOffset().negate());
// Downlink delay
final Gradient deltaT = arrivalDate.durationFrom(states[0].getDate());
final TimeStampedFieldPVCoordinates<Gradient> pvaDownlink = pvaLocal.shiftedBy(deltaT);
final Gradient tauD = signalTimeOfFlight(remotePV, arrivalDate,
pvaDownlink.getPosition(), arrivalDate,
states[0].getFrame());
// Remote satellite at signal emission
final FieldAbsoluteDate<Gradient> emissionDate = arrivalDate.shiftedBy(tauD.negate());
final QuadraticFieldClockModel<Gradient> remoteClock = getRemoteClock(nbEstimatedParams, parameterIndices);
final FieldClockOffset<Gradient> remoteClockOffset = remoteClock.getOffset(emissionDate);
return new OnBoardCommonParametersWithDerivatives(states[0], parameterIndices,
localClockOffset.getOffset(), localClockOffset.getRate(),
remoteClockOffset.getOffset(), remoteClockOffset.getRate(),
tauD, pvaDownlink,
remotePV.getPVCoordinates(emissionDate, states[0].getFrame()));
}
}