Phase.java
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* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
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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.AbstractParticipant;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.EstimatedMeasurementBase;
import org.orekit.estimation.measurements.MeasurementQuality;
import org.orekit.estimation.measurements.ObservableSatellite;
import org.orekit.estimation.measurements.Observer;
import org.orekit.estimation.measurements.SignalBasedMeasurement;
import org.orekit.frames.FieldTransform;
import org.orekit.frames.Frame;
import org.orekit.frames.Transform;
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.utils.Constants;
import org.orekit.utils.FieldPVCoordinates;
import org.orekit.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.PVCoordinates;
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;
/** Class modeling a phase measurement from a ground station.
* <p>
* The measurement is considered to be a signal emitted from
* a spacecraft and received on a ground station.
* Its value is the number of cycles between emission and
* reception. The motion of both the station and the
* spacecraft during the signal flight time are taken into
* account. The date of the measurement corresponds to the
* reception on ground of the emitted signal.
* </p>
* @author Thierry Ceolin
* @author Luc Maisonobe
* @author Maxime Journot
* @since 9.2
*/
public class Phase extends SignalBasedMeasurement<Phase> {
/** Type of the measurement. */
public static final String MEASUREMENT_TYPE = "Phase";
/** Driver for ambiguity. */
private final AmbiguityDriver ambiguityDriver;
/** Wavelength of the phase observed value [m]. */
private final double wavelength;
/** Observer that receives signal from satellite. */
private final Observer observer;
/** Simple constructor.
* @param observer observer that performs the measurement
* @param date date of the measurement
* @param phase observed value (cycles)
* @param wavelength phase observed value wavelength (m)
* @param sigma theoretical standard deviation
* @param baseWeight base weight
* @param satellite satellite related to this measurement
* @param cache from which ambiguity drive should come
* @since 12.1
*/
public Phase(final Observer observer, final AbsoluteDate date,
final double phase, final double wavelength, final double sigma,
final double baseWeight, final ObservableSatellite satellite,
final AmbiguityCache cache) {
this(observer, date, phase, wavelength, new MeasurementQuality(sigma, baseWeight), new SignalTravelTimeModel(),
satellite, cache);
}
/** Simple constructor.
* @param observer observer that performs the measurement
* @param date date of the measurement
* @param phase observed value (cycles)
* @param wavelength phase observed value wavelength (m)
* @param measurementQuality measurement quality data as used in orbit determination
* @param signalTravelTimeModel signal model
* @param satellite satellite related to this measurement
* @param cache from which ambiguity drive should come
* @since 14.0
*/
public Phase(final Observer observer, final AbsoluteDate date,
final double phase, final double wavelength, final MeasurementQuality measurementQuality,
final SignalTravelTimeModel signalTravelTimeModel, final ObservableSatellite satellite,
final AmbiguityCache cache) {
super(date, false, phase, measurementQuality, signalTravelTimeModel,
Collections.singletonList(satellite));
ambiguityDriver = cache.getAmbiguity(satellite.getName(), observer.getName(), wavelength);
addParametersDrivers(observer.getParametersDrivers());
addParameterDriver(ambiguityDriver);
this.observer = observer;
this.wavelength = wavelength;
}
/** Get receiving observer.
* @return observer
*/
public final Observer getObserver() {
return observer;
}
/** Get the wavelength.
* @return wavelength (m)
*/
public double getWavelength() {
return wavelength;
}
/** Get the driver for phase ambiguity.
* @return the driver for phase ambiguity
* @since 10.3
*/
public AmbiguityDriver getAmbiguityDriver() {
return ambiguityDriver;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurementBase<Phase> theoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
// Coordinates of the measured spacecraft
final SpacecraftState state = states[0];
final Frame frame = state.getFrame();
final TimeStampedPVCoordinates pva = state.getPVCoordinates();
// transform between remote observer frame and inertial frame
final AbsoluteDate measurementDate = getDate();
final Transform offsetToInertialDownlink = getObserver().getOffsetToInertial(frame, measurementDate, false);
final AbsoluteDate downlinkDate = offsetToInertialDownlink.getDate();
// Observer position in inertial frame at end of the downlink leg
final TimeStampedPVCoordinates origin = new TimeStampedPVCoordinates(downlinkDate, PVCoordinates.ZERO);
final TimeStampedPVCoordinates satelliteDownlink = offsetToInertialDownlink.transformPVCoordinates(origin);
// Coordinates provider for emitting object (observed spacecraft)
final PVCoordinatesProvider pvCoordinatesProvider = AbstractParticipant.extractPVCoordinatesProvider(states[0], pva);
// Downlink delay / determine time of emission of signal by ObservableSatellite
final AdjustableEmitterSignalTimer signalTimeOfFlight = getSignalTravelTimeModel()
.getAdjustableEmitterComputer(pvCoordinatesProvider);
final SignalReceptionCondition receptionCondition = new SignalReceptionCondition(downlinkDate,
satelliteDownlink.getPosition(), frame);
final double tauD = signalTimeOfFlight.computeDelay(receptionCondition, pva.getDate());
// Transit state & Transit state (re)computed with gradients
final double delta = downlinkDate.durationFrom(state.getDate());
final double deltaMTauD = delta - tauD;
final SpacecraftState transitState = states[0].shiftedBy(deltaMTauD);
// prepare the evaluation
final EstimatedMeasurementBase<Phase> estimated =
new EstimatedMeasurementBase<>(this, iteration, evaluation,
new SpacecraftState[] {
transitState
}, new TimeStampedPVCoordinates[] {
transitState.getPVCoordinates(), satelliteDownlink
});
// Clock offsets
final ObservableSatellite satellite = getSatellites().get(0);
final double dts = satellite.getOffsetValue(state.getDate());
final double dtg = getObserver().getOffsetValue(getDate());
// Phase value
final double cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
final double ambiguity = ambiguityDriver.getValue(state.getDate());
final double phase = (tauD + dtg - dts) * cOverLambda + ambiguity;
estimated.setEstimatedValue(phase);
return estimated;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurement<Phase> theoreticalEvaluation(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
// Create the parameter indices map
final SpacecraftState state = states[0];
final Frame frame = state.getFrame();
final Map<String, Integer> paramIndices = getParameterIndices(states);
final int nbParams = 6 * states.length + paramIndices.size();
// Coordinates of the spacecraft expressed as a gradient
final TimeStampedFieldPVCoordinates<Gradient> pva = AbstractMeasurement.getCoordinates(states[0], 0, nbParams);
// transform between Observer object and inertial frame, expressed as a gradient
// The components of the Observer's position in offset frame are the 3 last derivative parameters
final FieldTransform<Gradient> offsetToInertialDownlink = getObserver().
getOffsetToInertial(frame, getDate(), nbParams, paramIndices);
final FieldAbsoluteDate<Gradient> downlinkDate = offsetToInertialDownlink.getFieldDate();
// Observer position in inertial frame at end of the downlink leg
final GradientField field = GradientField.getField(nbParams);
final TimeStampedFieldPVCoordinates<Gradient> satelliteDownlink =
offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDate,
FieldPVCoordinates.getZero(field)));
// Form coordinates provider
final FieldPVCoordinatesProvider<Gradient> fieldPVCoordinatesProvider = AbstractParticipant.extractFieldPVCoordinatesProvider(states[0], pva);
// Downlink delay
final FieldAdjustableEmitterSignalTimer<Gradient> fieldComputer = getSignalTravelTimeModel()
.getFieldAdjustableEmitterComputer(field, fieldPVCoordinatesProvider);
final FieldSignalReceptionCondition<Gradient> receptionCondition = new FieldSignalReceptionCondition<>(downlinkDate,
satelliteDownlink.getPosition(), frame);
final Gradient tauD = fieldComputer.computeDelay(receptionCondition, pva.getDate());
// Transit state & Transit state (re)computed with gradients
final Gradient delta = downlinkDate.durationFrom(states[0].getDate());
final Gradient deltaMTauD = tauD.negate().add(delta);
final SpacecraftState transitState = states[0].shiftedBy(deltaMTauD.getValue());
final FieldAbsoluteDate<Gradient> fieldDate = new FieldAbsoluteDate<>(field, states[0].getDate()).shiftedBy(deltaMTauD);
final TimeStampedFieldPVCoordinates<Gradient> transitPV = fieldPVCoordinatesProvider.getPVCoordinates(fieldDate, frame);
// prepare the evaluation
final EstimatedMeasurement<Phase> estimated =
new EstimatedMeasurement<>(this, iteration, evaluation,
new SpacecraftState[] { transitState},
new TimeStampedPVCoordinates[] {
transitPV.toTimeStampedPVCoordinates(),
satelliteDownlink.toTimeStampedPVCoordinates()});
// Clock offsets
final ObservableSatellite satellite = getSatellites().get(0);
final Gradient dts = satellite.getFieldOffsetValue(nbParams, state.getDate(), paramIndices);
final Gradient dtg = getObserver().getFieldOffsetValue(nbParams, getDate(), paramIndices);
// Phase value
final double cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
final Gradient ambiguity = ambiguityDriver.getValue(nbParams, paramIndices, state.getDate());
final Gradient phase = tauD.add(dtg).subtract(dts).multiply(cOverLambda).add(ambiguity);
estimated.setEstimatedValue(phase.getValue());
// Phase first order derivatives with respect to state
final double[] derivatives = phase.getGradient();
estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));
// Set first order derivatives with respect to parameters
for (final ParameterDriver driver : getParametersDrivers()) {
for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
final Integer index = paramIndices.get(span.getData());
if (index != null) {
estimated.setParameterDerivatives(driver, span.getStart(), derivatives[index]);
}
}
}
return estimated;
}
}