Phase.java
/* Copyright 2002-2024 CS GROUP
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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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*
* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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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.GroundReceiverCommonParametersWithDerivatives;
import org.orekit.estimation.measurements.GroundReceiverCommonParametersWithoutDerivatives;
import org.orekit.estimation.measurements.GroundReceiverMeasurement;
import org.orekit.estimation.measurements.GroundStation;
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;
/** 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 GroundReceiverMeasurement<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;
/** Simple constructor.
* @param station ground station from which measurement is performed
* @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 GroundStation station, final AbsoluteDate date,
final double phase, final double wavelength, final double sigma,
final double baseWeight, final ObservableSatellite satellite,
final AmbiguityCache cache) {
super(station, false, date, phase, sigma, baseWeight, satellite);
ambiguityDriver = cache.getAmbiguity(satellite.getName(),
station.getBaseFrame().getName(),
wavelength);
addParameterDriver(ambiguityDriver);
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
* @since 10.3
*/
public AmbiguityDriver getAmbiguityDriver() {
return ambiguityDriver;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurementBase<Phase> theoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
final GroundReceiverCommonParametersWithoutDerivatives common = computeCommonParametersWithout(states[0]);
// prepare the evaluation
final EstimatedMeasurementBase<Phase> estimated =
new EstimatedMeasurementBase<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getTransitState()
}, new TimeStampedPVCoordinates[] {
common.getTransitPV(),
common.getStationDownlink()
});
// Clock offsets
final ObservableSatellite satellite = getSatellites().get(0);
final double dts = satellite.getClockOffsetDriver().getValue(common.getState().getDate());
final double dtg = getStation().getClockOffsetDriver().getValue(getDate());
// Phase value
final double cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
final double ambiguity = ambiguityDriver.getValue(common.getState().getDate());
final double phase = (common.getTauD() + dtg - dts) * cOverLambda + ambiguity;
estimated.setEstimatedValue(phase);
return estimated;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurement<Phase> theoreticalEvaluation(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
final SpacecraftState state = states[0];
// Phase derivatives are computed with respect to spacecraft state in inertial frame
// and station parameters
// ----------------------
//
// Parameters:
// - 0..2 - Position of the spacecraft in inertial frame
// - 3..5 - Velocity of the spacecraft in inertial frame
// - 6..n - station parameters (ambiguity, clock offset, station offsets, pole, prime meridian...)
final GroundReceiverCommonParametersWithDerivatives common = computeCommonParametersWithDerivatives(state);
final int nbParams = common.getTauD().getFreeParameters();
// prepare the evaluation
final EstimatedMeasurement<Phase> estimated =
new EstimatedMeasurement<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getTransitState()
}, new TimeStampedPVCoordinates[] {
common.getTransitPV().toTimeStampedPVCoordinates(),
common.getStationDownlink().toTimeStampedPVCoordinates()
});
// Clock offsets
final ObservableSatellite satellite = getSatellites().get(0);
final Gradient dts = satellite.getClockOffsetDriver().getValue(nbParams, common.getIndices(), state.getDate());
final Gradient dtg = getStation().getClockOffsetDriver().getValue(nbParams, common.getIndices(), getDate());
// Phase value
final double cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
final Gradient ambiguity = ambiguityDriver.getValue(nbParams, common.getIndices(), state.getDate());
final Gradient phase = common.getTauD().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 = common.getIndices().get(span.getData());
if (index != null) {
estimated.setParameterDerivatives(driver, span.getStart(), derivatives[index]);
}
}
}
return estimated;
}
}