OnBoardAntennaInterSatellitesRangeModifier.java
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package org.orekit.estimation.measurements.modifiers;
import java.util.Collections;
import java.util.List;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.estimation.measurements.EstimatedMeasurementBase;
import org.orekit.estimation.measurements.EstimationModifier;
import org.orekit.estimation.measurements.InterSatellitesRange;
import org.orekit.frames.StaticTransform;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.TimeStampedPVCoordinates;
/** On-board antenna offset effect on inter-satellites range measurements.
* @author Luc Maisonobe
* @since 9.0
*/
public class OnBoardAntennaInterSatellitesRangeModifier implements EstimationModifier<InterSatellitesRange> {
/** Position of the Antenna Phase Center in satellite 1 frame. */
private final Vector3D antennaPhaseCenter1;
/** Position of the Antenna Phase Center in satellite 2 frame. */
private final Vector3D antennaPhaseCenter2;
/** Simple constructor.
* @param antennaPhaseCenter1 position of the Antenna Phase Center in satellite 1 frame
* (i.e. the satellite which receives the signal and performs the measurement)
* @param antennaPhaseCenter2 position of the Antenna Phase Center in satellite 2 frame
* (i.e. the satellite which simply emits the signal in the one-way
* case, or reflects the signal in the two-way case)
*/
public OnBoardAntennaInterSatellitesRangeModifier(final Vector3D antennaPhaseCenter1,
final Vector3D antennaPhaseCenter2) {
this.antennaPhaseCenter1 = antennaPhaseCenter1;
this.antennaPhaseCenter2 = antennaPhaseCenter2;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return Collections.emptyList();
}
/** {@inheritDoc} */
@Override
public void modifyWithoutDerivatives(final EstimatedMeasurementBase<InterSatellitesRange> estimated) {
if (estimated.getParticipants().length < 3) {
modifyOneWay(estimated);
} else {
modifyTwoWay(estimated);
}
}
/** Apply a modifier to an estimated measurement in the one-way case.
* @param estimated estimated measurement to modify
*/
private void modifyOneWay(final EstimatedMeasurementBase<InterSatellitesRange> estimated) {
// the participants are satellite 2 at emission, satellite 1 at reception
final TimeStampedPVCoordinates[] participants = estimated.getParticipants();
final AbsoluteDate emissionDate = participants[0].getDate();
final AbsoluteDate receptionDate = participants[1].getDate();
// transforms from spacecraft to inertial frame at emission/reception dates
final SpacecraftState refState1 = estimated.getStates()[0];
final SpacecraftState receptionState = refState1.shiftedBy(receptionDate.durationFrom(refState1.getDate()));
final StaticTransform receptionSpacecraftToInert = receptionState.toStaticTransform().getInverse();
final SpacecraftState refState2 = estimated.getStates()[1];
final SpacecraftState emissionState = refState2.shiftedBy(emissionDate.durationFrom(refState2.getDate()));
final StaticTransform emissionSpacecraftToInert = emissionState.toStaticTransform().getInverse();
// compute the geometrical value of the inter-satellites range directly from participants positions.
// Note that this may be different from the value returned by estimated.getEstimatedValue(),
// because other modifiers may already have been taken into account
final Vector3D pSpacecraftReception = receptionSpacecraftToInert.transformPosition(Vector3D.ZERO);
final Vector3D pSpacecraftEmission = emissionSpacecraftToInert.transformPosition(Vector3D.ZERO);
final double interSatellitesRangeUsingSpacecraftCenter =
Vector3D.distance(pSpacecraftEmission, pSpacecraftReception);
// compute the geometrical value of the range replacing
// the spacecraft positions with antenna phase center positions
final Vector3D pAPCReception = receptionSpacecraftToInert.transformPosition(antennaPhaseCenter1);
final Vector3D pAPCEmission = emissionSpacecraftToInert.transformPosition(antennaPhaseCenter2);
final double interSatellitesRangeUsingAntennaPhaseCenter =
Vector3D.distance(pAPCEmission, pAPCReception);
// get the estimated value before this modifier is applied
final double[] value = estimated.getEstimatedValue();
// modify the value
value[0] += interSatellitesRangeUsingAntennaPhaseCenter - interSatellitesRangeUsingSpacecraftCenter;
estimated.setEstimatedValue(value);
}
/** Apply a modifier to an estimated measurement in the two-way case.
* @param estimated estimated measurement to modify
*/
private void modifyTwoWay(final EstimatedMeasurementBase<InterSatellitesRange> estimated) {
// the participants are satellite 1 at emission, satellite 2 at transit, satellite 1 at reception
final TimeStampedPVCoordinates[] participants = estimated.getParticipants();
final AbsoluteDate emissionDate = participants[0].getDate();
final AbsoluteDate transitDate = participants[1].getDate();
final AbsoluteDate receptionDate = participants[2].getDate();
// transforms from spacecraft to inertial frame at emission/reception dates
final SpacecraftState refState1 = estimated.getStates()[0];
final SpacecraftState receptionState = refState1.shiftedBy(receptionDate.durationFrom(refState1.getDate()));
final StaticTransform receptionSpacecraftToInert = receptionState.toStaticTransform().getInverse();
final SpacecraftState refState2 = estimated.getStates()[1];
final SpacecraftState transitState = refState2.shiftedBy(transitDate.durationFrom(refState2.getDate()));
final StaticTransform transitSpacecraftToInert = transitState.toStaticTransform().getInverse();
final SpacecraftState emissionState = refState1.shiftedBy(emissionDate.durationFrom(refState1.getDate()));
final StaticTransform emissionSpacecraftToInert = emissionState.toStaticTransform().getInverse();
// compute the geometrical value of the inter-satellites range directly from participants positions.
// Note that this may be different from the value returned by estimated.getEstimatedValue(),
// because other modifiers may already have been taken into account
final Vector3D pSpacecraftReception = receptionSpacecraftToInert.transformPosition(Vector3D.ZERO);
final Vector3D pSpacecraftTransit = transitSpacecraftToInert.transformPosition(Vector3D.ZERO);
final Vector3D pSpacecraftEmission = emissionSpacecraftToInert.transformPosition(Vector3D.ZERO);
final double interSatellitesRangeUsingSpacecraftCenter =
0.5 * (Vector3D.distance(pSpacecraftEmission, pSpacecraftTransit) +
Vector3D.distance(pSpacecraftTransit, pSpacecraftReception));
// compute the geometrical value of the range replacing
// the spacecraft positions with antenna phase center positions
final Vector3D pAPCReception = receptionSpacecraftToInert.transformPosition(antennaPhaseCenter1);
final Vector3D pAPCTransit = transitSpacecraftToInert.transformPosition(antennaPhaseCenter2);
final Vector3D pAPCEmission = emissionSpacecraftToInert.transformPosition(antennaPhaseCenter1);
final double interSatellitesRangeUsingAntennaPhaseCenter =
0.5 * (Vector3D.distance(pAPCEmission, pAPCTransit) +
Vector3D.distance(pAPCTransit, pAPCReception));
// get the estimated value before this modifier is applied
final double[] value = estimated.getEstimatedValue();
// modify the value
value[0] += interSatellitesRangeUsingAntennaPhaseCenter - interSatellitesRangeUsingSpacecraftCenter;
estimated.setEstimatedValue(value);
}
}