Range.java
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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;
import java.util.Map;
import org.hipparchus.Field;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.orekit.frames.Frame;
import org.orekit.propagation.SpacecraftState;
import org.orekit.signal.FieldAdjustableEmitterSignalTimer;
import org.orekit.signal.FieldSignalReceptionCondition;
import org.orekit.signal.SignalTravelTimeModel;
import org.orekit.signal.TwoLeggedSignalTimer;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.Constants;
import org.orekit.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.TimeStampedPVCoordinates;
/** Class modeling a range measurement received by an observer.
* <p>
* For one-way measurements, a signal is emitted by the satellite
* and received by the observer. The measurement value is the
* elapsed time between emission and reception multiplied by c where
* c is the speed of light.
* </p>
* <p>
* For two-way measurements, the measurement is considered to be a signal
* emitted from a observer, reflected on spacecraft, and received
* on the same observer. Its value is the elapsed time between
* emission and reception multiplied by c/2 where c is the speed of light.
* </p>
* <p>
* The motion of both the sensor 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 or reflected signal.
* </p>
* <p>
* The clock offsets of both the observer and the satellite are taken
* into account. These offsets correspond to the values that must be subtracted
* from sensor (resp. satellite) reading of time to compute the real physical
* date. These offsets have two effects:
* </p>
* <ul>
* <li>as measurement date is evaluated at reception time, the real physical date
* of the measurement is the observed date to which the receiving observer
* clock offset is subtracted</li>
* <li>as range is evaluated using the total signal time of flight, for one-way
* measurements the observed range is the real physical signal time of flight to
* which (Δtg - Δts) ⨯ c is added, where Δtg (resp. Δts) is the clock offset for the
* receiving observer (resp. emitting satellite). A similar effect exists in
* two-way measurements but it is computed as (Δtg - Δtg) ⨯ c / 2 as the same clock
* is used for initial emission and final reception and therefore it evaluates
* to zero.</li>
* </ul>
* @author Thierry Ceolin
* @author Luc Maisonobe
* @author Maxime Journot
* @since 8.0
*/
public class Range extends AbstractRangeRelatedMeasurement<Range> {
/** Type of the measurement. */
public static final String MEASUREMENT_TYPE = "Range";
/** Simple constructor.
* @param observer observer that performs the measurement
* @param twoWay flag indicating whether it is a two-way measurement
* @param date date of the measurement
* @param range observed value
* @param sigma theoretical standard deviation
* @param baseWeight base weight
* @param satellite satellite related to this measurement
* @since 9.3
*/
public Range(final Observer observer, final boolean twoWay, final AbsoluteDate date,
final double range, final double sigma, final double baseWeight,
final ObservableSatellite satellite) {
super(observer, date, range, new MeasurementQuality(sigma, baseWeight), twoWay, new SignalTravelTimeModel(), satellite);
}
/** Simple constructor.
* @param observer observer that performs the measurement
* @param twoWay flag indicating whether it is a two-way measurement
* @param date date of the measurement
* @param range observed value
* @param measurementQuality measurement quality data as used in orbit determination
* @param signalTravelTimeModel signal model
* @param satellite satellite related to this measurement
* @since 14.0
*/
public Range(final Observer observer, final boolean twoWay, final AbsoluteDate date,
final double range, final MeasurementQuality measurementQuality,
final SignalTravelTimeModel signalTravelTimeModel, final ObservableSatellite satellite) {
super(observer, date, range, measurementQuality, twoWay, signalTravelTimeModel, satellite);
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurementBase<Range> theoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
// compute reception date
final double clockOffset = getObserver().getQuadraticClockModel().getOffset(getDate()).getBias();
final AbsoluteDate receptionDate = getDate().shiftedBy(-clockOffset);
if (isTwoWay()) {
return twoWayTheoreticalEvaluationWithoutDerivatives(iteration, evaluation, receptionDate, states[0]);
} else {
return oneWayTheoreticalEvaluationWithoutDerivatives(iteration, evaluation, receptionDate, states[0]);
}
}
/** Evaluate measurement in two-way without derivatives.
* @param iteration iteration number
* @param evaluation evaluations counter
* @param receptionDate signal final reception date
* @param state state
* @return theoretical value
* @since 14.0
*/
private EstimatedMeasurementBase<Range> twoWayTheoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final AbsoluteDate receptionDate,
final SpacecraftState state) {
final EstimatedMeasurementBase<Range> estimated = initializeTwoWayTheoreticalEvaluation(this, iteration, evaluation,
receptionDate, state);
// Compute range
final AbsoluteDate emissionDate = estimated.getParticipants()[0].getDate();
final double range = receptionDate.durationFrom(emissionDate) * Constants.SPEED_OF_LIGHT / 2.;
estimated.setEstimatedValue(range);
return estimated;
}
/** Evaluate measurement in one-way without derivatives.
* @param iteration iteration number
* @param evaluation evaluations counter
* @param receptionDate signal reception date
* @param state state
* @return theoretical value
* @since 14.0
*/
private EstimatedMeasurementBase<Range> oneWayTheoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final AbsoluteDate receptionDate,
final SpacecraftState state) {
final EstimatedMeasurementBase<Range> estimated = initializeOneWayTheoreticalEvaluation(this, iteration, evaluation,
receptionDate, state);
final AbsoluteDate emissionDate = estimated.getParticipants()[0].getDate();
// clock bias, taken in account only in case of one way
final ObservableSatellite satellite = getSatellites().get(0);
final double dts = satellite.getOffsetValue(emissionDate);
final double dtg = getObserver().getOffsetValue(receptionDate);
final double clockBias = dtg - dts;
final double range = (clockBias + receptionDate.durationFrom(emissionDate)) * Constants.SPEED_OF_LIGHT;
estimated.setEstimatedValue(range);
return estimated;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurement<Range> twoWayTheoreticalEvaluation(final int iteration, final int evaluation,
final FieldPVCoordinatesProvider<Gradient> satellitePVProvider,
final SpacecraftState state,
final Map<String, Integer> indices,
final int nbParams) {
// Compute light time delays
final Frame frame = state.getFrame();
final FieldPVCoordinatesProvider<Gradient> observerPVProvider = getObserver().getFieldPVCoordinatesProvider(nbParams, indices);
final FieldAbsoluteDate<Gradient> receptionDate = getCorrectedReceptionDateField(nbParams, indices);
final FieldVector3D<Gradient> receiverPosition = observerPVProvider.getPosition(receptionDate, frame);
final TwoLeggedSignalTimer twoLeggedSignalTimer = new TwoLeggedSignalTimer(getSignalTravelTimeModel());
final FieldSignalReceptionCondition<Gradient> receptionCondition = new FieldSignalReceptionCondition<>(receptionDate,
receiverPosition, frame);
final Gradient[] delays = twoLeggedSignalTimer.computeDelays(receptionCondition, satellitePVProvider, observerPVProvider);
// Prepare the evaluation
final FieldAbsoluteDate<Gradient> transitDate = receptionDate.shiftedBy(delays[1].negate());
final SpacecraftState transitState = state.shiftedBy(transitDate.toAbsoluteDate().durationFrom(state));
final FieldAbsoluteDate<Gradient> emissionDate = transitDate.shiftedBy(delays[0].negate());
final EstimatedMeasurement<Range> estimated = new EstimatedMeasurement<>(this, iteration, evaluation,
new SpacecraftState[] { transitState },
new TimeStampedPVCoordinates[] {
getObserver().getPVCoordinatesProvider().getPVCoordinates(emissionDate.toAbsoluteDate(), frame),
transitState.getPVCoordinates(),
getObserver().getPVCoordinatesProvider().getPVCoordinates(receptionDate.toAbsoluteDate(), frame)});
// Compute range
final Gradient range = delays[0].add(delays[1]).multiply(Constants.SPEED_OF_LIGHT / 2.);
fillEstimation(range, indices, estimated);
return estimated;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurement<Range> oneWayTheoreticalEvaluation(final int iteration, final int evaluation,
final FieldPVCoordinatesProvider<Gradient> satellitePVProvider,
final SpacecraftState state,
final Map<String, Integer> indices,
final int nbParams) {
// compute reception and emission dates
final FieldAbsoluteDate<Gradient> receptionDate = getCorrectedReceptionDateField(nbParams, indices);
final Frame frame = state.getFrame();
final Field<Gradient> field = receptionDate.getField();
final FieldAdjustableEmitterSignalTimer<Gradient> adjustableEmitter = getSignalTravelTimeModel().getFieldAdjustableEmitterComputer(
field, satellitePVProvider);
final FieldVector3D<Gradient> observerPositionAtReception = getObserver().getFieldPVCoordinatesProvider(nbParams, indices)
.getPosition(receptionDate, frame);
final FieldSignalReceptionCondition<Gradient> receptionCondition = new FieldSignalReceptionCondition<>(receptionDate,
observerPositionAtReception, frame);
final Gradient delay = adjustableEmitter.computeDelay(receptionCondition);
// prepare the evaluation
final FieldAbsoluteDate<Gradient> emissionDate = receptionDate.shiftedBy(delay.negate());
final SpacecraftState emissionState = state.shiftedBy(emissionDate.toAbsoluteDate().durationFrom(state));
final EstimatedMeasurement<Range> estimated =
new EstimatedMeasurement<>(this, iteration, evaluation,
new SpacecraftState[] { emissionState }, new TimeStampedPVCoordinates[] {
emissionState.getPVCoordinates(),
getObserver().getPVCoordinatesProvider().getPVCoordinates(receptionDate.toAbsoluteDate(), frame) });
// clock offset, taken in account only in case of one way
final ObservableSatellite satellite = getSatellites().get(0);
final Gradient dts = satellite.getFieldOffsetValue(nbParams, emissionDate.toAbsoluteDate(), indices);
final Gradient dtg = getObserver().getFieldOffsetValue(nbParams, receptionDate.toAbsoluteDate(), indices);
final Gradient clockBias = dtg.subtract(dts);
final Gradient range = clockBias.add(delay).multiply(Constants.SPEED_OF_LIGHT);
fillEstimation(range, indices, estimated);
return estimated;
}
}