InterSatellitesPhase.java
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* CS licenses this file to You under the Apache License, Version 2.0
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*
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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.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;
/** Phase measurement between two satellites.
* <p>
* The measurement is considered to be a signal emitted from
* a remote satellite and received by a local satellite.
* Its value is the number of cycles between emission and reception.
* The motion of both 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 Bryan Cazabonne
* @since 10.3
*/
public class InterSatellitesPhase extends AbstractInterSatellitesMeasurement<InterSatellitesPhase> {
/** Type of the measurement. */
public static final String MEASUREMENT_TYPE = "InterSatellitesPhase";
/** Driver for ambiguity. */
private final AmbiguityDriver ambiguityDriver;
/** Wavelength of the phase observed value [m]. */
private final double wavelength;
/** Constructor.
* @param local satellite which receives the signal and performs the measurement
* @param remote remote satellite which simply emits the signal
* @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 cache from which ambiguity drive should come
* @since 12.1
*/
public InterSatellitesPhase(final ObservableSatellite local,
final ObservableSatellite remote,
final AbsoluteDate date, final double phase,
final double wavelength, final double sigma,
final double baseWeight,
final AmbiguityCache cache) {
// Call to super constructor
super(date, phase, sigma, baseWeight, local, remote);
// Initialize phase ambiguity driver
ambiguityDriver = cache.getAmbiguity(remote.getName(), local.getName(), wavelength);
// Add parameter drivers
addParameterDriver(ambiguityDriver);
// Initialize 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 ParameterDriver getAmbiguityDriver() {
return ambiguityDriver;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurementBase<InterSatellitesPhase> theoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
final OnBoardCommonParametersWithoutDerivatives common = computeCommonParametersWithout(states, false);
// prepare the evaluation
final EstimatedMeasurementBase<InterSatellitesPhase> estimatedPhase =
new EstimatedMeasurementBase<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getState(),
states[1]
}, 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;
estimatedPhase.setEstimatedValue(phase);
// Return the estimated measurement
return estimatedPhase;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurement<InterSatellitesPhase> theoreticalEvaluation(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
final OnBoardCommonParametersWithDerivatives common = computeCommonParametersWith(states, false);
// prepare the evaluation
final EstimatedMeasurement<InterSatellitesPhase> estimatedPhase =
new EstimatedMeasurement<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getState(),
states[1]
}, 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);
estimatedPhase.setEstimatedValue(phase.getValue());
// Range first order derivatives with respect to states
final double[] derivatives = phase.getGradient();
estimatedPhase.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));
estimatedPhase.setStateDerivatives(1, Arrays.copyOfRange(derivatives, 6, 12));
// 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 = common.getIndices().get(span.getData());
if (index != null) {
estimatedPhase.setParameterDerivatives(driver, span.getStart(), derivatives[index]);
}
}
}
// Return the estimated measurement
return estimatedPhase;
}
}