Phase.java
/* Copyright 2002-2020 CS GROUP
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* 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,
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package org.orekit.estimation.measurements.gnss;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.analysis.differentiation.GradientField;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.orekit.estimation.measurements.AbstractMeasurement;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.GroundStation;
import org.orekit.estimation.measurements.ObservableSatellite;
import org.orekit.frames.FieldTransform;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.Constants;
import org.orekit.utils.ParameterDriver;
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 AbstractMeasurement<Phase> {
/** Name for ambiguity driver. */
public static final String AMBIGUITY_NAME = "ambiguity";
/** Driver for ambiguity. */
private final ParameterDriver ambiguityDriver;
/** Ground station from which measurement is performed. */
private final GroundStation station;
/** 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
* @since 9.3
*/
public Phase(final GroundStation station, final AbsoluteDate date,
final double phase, final double wavelength, final double sigma,
final double baseWeight, final ObservableSatellite satellite) {
super(date, phase, sigma, baseWeight, Arrays.asList(satellite));
ambiguityDriver = new ParameterDriver(AMBIGUITY_NAME,
0.0, 1.0,
Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
addParameterDriver(ambiguityDriver);
addParameterDriver(station.getClockOffsetDriver());
addParameterDriver(station.getEastOffsetDriver());
addParameterDriver(station.getNorthOffsetDriver());
addParameterDriver(station.getZenithOffsetDriver());
addParameterDriver(station.getPrimeMeridianOffsetDriver());
addParameterDriver(station.getPrimeMeridianDriftDriver());
addParameterDriver(station.getPolarOffsetXDriver());
addParameterDriver(station.getPolarDriftXDriver());
addParameterDriver(station.getPolarOffsetYDriver());
addParameterDriver(station.getPolarDriftYDriver());
this.station = station;
this.wavelength = wavelength;
}
/** Get the ground station from which measurement is performed.
* @return ground station from which measurement is performed
*/
public GroundStation getStation() {
return station;
}
/** Get the wavelength.
* @return wavelength (m)
*/
public double getWavelength() {
return wavelength;
}
/** {@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...)
int nbParams = 6;
final Map<String, Integer> indices = new HashMap<>();
for (ParameterDriver driver : getParametersDrivers()) {
if (driver.isSelected()) {
indices.put(driver.getName(), nbParams++);
}
}
final FieldVector3D<Gradient> zero = FieldVector3D.getZero(GradientField.getField(nbParams));
// Coordinates of the spacecraft expressed as a gradient
final TimeStampedFieldPVCoordinates<Gradient> pvaDS = getCoordinates(state, 0, nbParams);
// transform between station and inertial frame, expressed as a gradient
// The components of station's position in offset frame are the 3 last derivative parameters
final FieldTransform<Gradient> offsetToInertialDownlink =
station.getOffsetToInertial(state.getFrame(), getDate(), nbParams, indices);
final FieldAbsoluteDate<Gradient> downlinkDateDS =
offsetToInertialDownlink.getFieldDate();
// Station position in inertial frame at end of the downlink leg
final TimeStampedFieldPVCoordinates<Gradient> stationDownlink =
offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
zero, zero, zero));
// Compute propagation times
// (if state has already been set up to pre-compensate propagation delay,
// we will have delta == tauD and transitState will be the same as state)
// Downlink delay
final Gradient tauD = signalTimeOfFlight(pvaDS, stationDownlink.getPosition(), downlinkDateDS);
// Transit state & Transit state (re)computed with gradients
final Gradient delta = downlinkDateDS.durationFrom(state.getDate());
final Gradient deltaMTauD = tauD.negate().add(delta);
final SpacecraftState transitState = state.shiftedBy(deltaMTauD.getValue());
final TimeStampedFieldPVCoordinates<Gradient> transitStateDS = pvaDS.shiftedBy(deltaMTauD);
// prepare the evaluation
final EstimatedMeasurement<Phase> estimated =
new EstimatedMeasurement<Phase>(this, iteration, evaluation,
new SpacecraftState[] {
transitState
}, new TimeStampedPVCoordinates[] {
transitStateDS.toTimeStampedPVCoordinates(),
stationDownlink.toTimeStampedPVCoordinates()
});
// Clock offsets
final ObservableSatellite satellite = getSatellites().get(0);
final Gradient dts = satellite.getClockOffsetDriver().getValue(nbParams, indices);
final Gradient dtg = station.getClockOffsetDriver().getValue(nbParams, indices);
// Phase value
final double cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
final Gradient ambiguity = ambiguityDriver.getValue(nbParams, indices);
final Gradient phase = tauD.add(dtg).subtract(dts).multiply(cOverLambda).add(ambiguity);
estimated.setEstimatedValue(phase.getValue());
// Phase partial derivatives with respect to state
final double[] derivatives = phase.getGradient();
estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));
// set partial derivatives with respect to parameters
// (beware element at index 0 is the value, not a derivative)
for (final ParameterDriver driver : getParametersDrivers()) {
final Integer index = indices.get(driver.getName());
if (index != null) {
estimated.setParameterDerivatives(driver, derivatives[index]);
}
}
return estimated;
}
}