OneWayGNSSPhase.java
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package org.orekit.estimation.measurements.gnss;
import java.util.Arrays;
import org.hipparchus.analysis.differentiation.Gradient;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.EstimatedMeasurementBase;
import org.orekit.estimation.measurements.ObservableSatellite;
import org.orekit.estimation.measurements.ObserverSatellite;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.Constants;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.TimeSpanMap.Span;
import org.orekit.utils.TimeStampedPVCoordinates;
/** One-way GNSS phase measurement.
* <p>
* This class can be used in precise orbit determination applications
* for modeling a phase measurement between a GNSS satellite (emitter)
* and a LEO satellite (receiver).
* <p>
* The one-way GNSS phase measurement assumes knowledge of the orbit and
* the clock offset of the emitting GNSS satellite. For instance, it is
* possible to use a SP3 file or a GNSS navigation message to recover
* the satellite's orbit and clock.
* <p>
* This class is very similar to {@link InterSatellitesPhase} measurement
* class. However, using the one-way GNSS phase measurement, the orbit and clock
* of the emitting GNSS satellite are <b>NOT</b> estimated simultaneously with
* LEO satellite coordinates.
*
* @author Bryan Cazabonne
* @since 10.3
*/
public class OneWayGNSSPhase extends AbstractOneWayGNSSMeasurement<OneWayGNSSPhase> {
/** Type of the measurement. */
public static final String MEASUREMENT_TYPE = "OneWayGNSSPhase";
/** Driver for ambiguity. */
private final AmbiguityDriver ambiguityDriver;
/** Wavelength of the phase observed value [m]. */
private final double wavelength;
/** Simple constructor.
* @param gnssSatellite GNSS observer satellite
* @param date date of the measurement
* @param phase observed value, in cycles
* @param wavelength phase observed value wavelength, in meters
* @param sigma theoretical standard deviation
* @param baseWeight base weight
* @param local satellite which receives the signal and perform the measurement
* @param cache from which ambiguity drive should come
* @since 12.1
*/
public OneWayGNSSPhase(final ObserverSatellite gnssSatellite,
final AbsoluteDate date,
final double phase, final double wavelength, final double sigma,
final double baseWeight, final ObservableSatellite local,
final AmbiguityCache cache) {
// Call super constructor
super(gnssSatellite, date, phase, sigma, baseWeight, local);
// Initialize phase ambiguity driver
ambiguityDriver = cache.getAmbiguity(gnssSatellite.getName(), local.getName(), wavelength);
// The local satellite clock offset affects the measurement
addParameterDriver(ambiguityDriver);
// Initialise fields
this.wavelength = wavelength;
}
/** Get the wavelength.
* @return wavelength (m)
*/
public double getWavelength() {
return wavelength;
}
/** Get the driver for phase ambiguity.
* @return the driver for phase ambiguity
*/
public AmbiguityDriver getAmbiguityDriver() {
return ambiguityDriver;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurementBase<OneWayGNSSPhase> theoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
final OnBoardCommonParametersWithoutDerivatives common = computeCommonParametersWithout(states, false);
// prepare the evaluation
final EstimatedMeasurementBase<OneWayGNSSPhase> estimatedPhase =
new EstimatedMeasurementBase<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getState()
}, new TimeStampedPVCoordinates[] {
common.getRemotePV(),
common.getTransitPV()
});
// Phase value
final double cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
final double ambiguity = ambiguityDriver.getValue(common.getState().getDate());
final double phase = (common.getTauD() + common.getLocalOffset() - common.getRemoteOffset()) * cOverLambda +
ambiguity;
// Set value of the estimated measurement
estimatedPhase.setEstimatedValue(phase);
// Return the estimated measurement
return estimatedPhase;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurement<OneWayGNSSPhase> theoreticalEvaluation(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
final OnBoardCommonParametersWithDerivatives common = computeCommonParametersWith(states, false);
// prepare the evaluation
final EstimatedMeasurement<OneWayGNSSPhase> estimatedPhase =
new EstimatedMeasurement<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getState()
}, new TimeStampedPVCoordinates[] {
common.getRemotePV().toTimeStampedPVCoordinates(),
common.getTransitPV().toTimeStampedPVCoordinates()
});
// Phase value
final double cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
final Gradient ambiguity = ambiguityDriver.getValue(common.getTauD().getFreeParameters(), common.getIndices(),
common.getState().getDate());
final Gradient phase = common.getTauD().add(common.getLocalOffset()).subtract(common.getRemoteOffset()).
multiply(cOverLambda).
add(ambiguity);
final double[] phaseDerivatives = phase.getGradient();
// Set value and state first order derivatives of the estimated measurement
estimatedPhase.setEstimatedValue(phase.getValue());
estimatedPhase.setStateDerivatives(0, Arrays.copyOfRange(phaseDerivatives, 0, 6));
// Set first order derivatives with respect to parameters
for (final ParameterDriver phaseMeasurementDriver : getParametersDrivers()) {
for (Span<String> span = phaseMeasurementDriver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
final Integer index = common.getIndices().get(span.getData());
if (index != null) {
estimatedPhase.setParameterDerivatives(phaseMeasurementDriver, span.getStart(), phaseDerivatives[index]);
}
}
}
// Return the estimated measurement
return estimatedPhase;
}
}