TwoLegsSignalTravelTimer.java
/* Copyright 2022-2026 Romain Serra
* Licensed to CS GROUP (CS) under one or more
* 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,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.estimation.measurements.signal;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.MathArrays;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.PVCoordinatesProvider;
/**
* Class for two-way signal travel time.
* A signal is emitted, received a first time (relay/reflection) and received again a final time. There is no further assumption.
* @since 14.0
* @author Romain Serra
*/
public class TwoLegsSignalTravelTimer {
/** Signal travel time model. */
private final SignalTravelTimeModel signalTravelTimeModel;
/**
* Constructor.
* @param signalTravelTimeModel time delay computer
*/
public TwoLegsSignalTravelTimer(final SignalTravelTimeModel signalTravelTimeModel) {
this.signalTravelTimeModel = signalTravelTimeModel;
}
/**
* Compute first and second leg delays.
*
* @param frame frame where position is given
* @param receiverPosition end receiver position (at reception)
* @param receptionDate signal end reception date
* @param relay signal relay (initial reception) coordinates provider
* @param approxRelayDate guess for the relay date
* @param emitter signal initial emitter coordinates provider
* @param approxEmissionDate guess for the emission date
* @return delays on both legs in chronological order (s)
*/
public double[] computeDelays(final Frame frame, final Vector3D receiverPosition, final AbsoluteDate receptionDate,
final PVCoordinatesProvider relay, final AbsoluteDate approxRelayDate,
final PVCoordinatesProvider emitter, final AbsoluteDate approxEmissionDate) {
final double secondLegTravelTime = computeTravelTime(frame, receiverPosition, receptionDate, relay, approxRelayDate);
final AbsoluteDate relayDate = receptionDate.shiftedBy(-secondLegTravelTime);
final Vector3D relayPosition = relay.getPosition(relayDate, frame);
final double firstLegTravelTime = computeTravelTime(frame, relayPosition, relayDate, emitter, approxEmissionDate);
return new double[] { firstLegTravelTime, secondLegTravelTime };
}
/**
* Compute first and second leg delays without guess.
*
* @param frame frame where position is given
* @param receiverPosition end receiver position (at reception)
* @param receptionDate signal end reception date
* @param relay signal relay (initial reception) coordinates provider
* @param emitter signal initial emitter coordinates provider
* @return delays on both legs in chronological order (s)
*/
public double[] computeDelays(final Frame frame, final Vector3D receiverPosition, final AbsoluteDate receptionDate,
final PVCoordinatesProvider relay, final PVCoordinatesProvider emitter) {
final double secondLegTravelTime = computeTravelTime(frame, receiverPosition, receptionDate, relay, receptionDate);
final AbsoluteDate relayDate = receptionDate.shiftedBy(-secondLegTravelTime);
final Vector3D relayPosition = relay.getPosition(relayDate, frame);
final double firstLegTravelTime = computeTravelTime(frame, relayPosition, relayDate, emitter, relayDate);
return new double[] { firstLegTravelTime, secondLegTravelTime };
}
/**
* Compute first and second leg delays.
* @param <T> field type
* @param frame frame where position is given
* @param receiverPosition end receiver position (at reception)
* @param receptionDate signal end reception date
* @param relay signal relay (initial reception, second emission) coordinates provider
* @param approxRelayDate guess for the relay date
* @param emitter signal initial emitter coordinates provider
* @param approxEmissionDate guess for the emission date
* @return delays on both legs in chronological order (s)
*/
public <T extends CalculusFieldElement<T>> T[] computeDelays(final Frame frame, final FieldVector3D<T> receiverPosition,
final FieldAbsoluteDate<T> receptionDate,
final FieldPVCoordinatesProvider<T> relay,
final FieldAbsoluteDate<T> approxRelayDate,
final FieldPVCoordinatesProvider<T> emitter,
final FieldAbsoluteDate<T> approxEmissionDate) {
final T secondLegTravelTime = computeTravelTime(frame, receiverPosition, receptionDate, relay, approxRelayDate);
final FieldAbsoluteDate<T> relayDate = receptionDate.shiftedBy(secondLegTravelTime.negate());
final FieldVector3D<T> relayPosition = relay.getPosition(relayDate, frame);
final T firstLegTravelTime = computeTravelTime(frame, relayPosition, relayDate, emitter, approxEmissionDate);
final T[] output = MathArrays.buildArray(receiverPosition.getX().getField(), 2);
output[0] = firstLegTravelTime;
output[1] = secondLegTravelTime;
return output;
}
/**
* Compute first and second leg delays without guess.
* @param <T> field type
* @param frame frame where position is given
* @param receiverPosition end receiver position (at reception)
* @param receptionDate signal end reception date
* @param relay signal relay (initial reception, second emission) coordinates provider
* @param emitter signal initial emitter coordinates provider
* @return delays on both legs in chronological order (s)
*/
public <T extends CalculusFieldElement<T>> T[] computeDelays(final Frame frame, final FieldVector3D<T> receiverPosition,
final FieldAbsoluteDate<T> receptionDate,
final FieldPVCoordinatesProvider<T> relay,
final FieldPVCoordinatesProvider<T> emitter) {
final T secondLegTravelTime = computeTravelTime(frame, receiverPosition, receptionDate, relay, receptionDate);
final FieldAbsoluteDate<T> relayDate = receptionDate.shiftedBy(secondLegTravelTime.negate());
final FieldVector3D<T> relayPosition = relay.getPosition(relayDate, frame);
final T firstLegTravelTime = computeTravelTime(frame, relayPosition, relayDate, emitter, relayDate);
final T[] output = MathArrays.buildArray(receiverPosition.getX().getField(), 2);
output[0] = firstLegTravelTime;
output[1] = secondLegTravelTime;
return output;
}
/**
* Method for one leg travel time.
* @param frame frame where position is given
* @param receiverPosition receiver position at reception
* @param receptionDate reception date
* @param emitter emitter
* @param guessEmissionDate guess for the emission date
* @return signal travel time
*/
private double computeTravelTime(final Frame frame, final Vector3D receiverPosition, final AbsoluteDate receptionDate,
final PVCoordinatesProvider emitter, final AbsoluteDate guessEmissionDate) {
return signalTravelTimeModel.getAdjustableEmitterComputer(emitter).computeDelay(guessEmissionDate,
receiverPosition, receptionDate, frame);
}
/**
* Method for one leg travel time.
* @param <T> field type
* @param frame frame where position is given
* @param receiverPosition receiver position at reception
* @param receptionDate reception date
* @param emitter emitter
* @param guessEmissionDate guess for the emission date
* @return signal travel time
*/
private <T extends CalculusFieldElement<T>> T computeTravelTime(final Frame frame, final FieldVector3D<T> receiverPosition,
final FieldAbsoluteDate<T> receptionDate,
final FieldPVCoordinatesProvider<T> emitter,
final FieldAbsoluteDate<T> guessEmissionDate) {
return signalTravelTimeModel.getFieldAdjustableEmitterComputer(receptionDate.getField(), emitter)
.computeDelay(guessEmissionDate, receiverPosition, receptionDate, frame);
}
}