OnBoardAntennaPhaseModifier.java
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* http://www.apache.org/licenses/LICENSE-2.0
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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.EstimatedMeasurement;
import org.orekit.estimation.measurements.EstimationModifier;
import org.orekit.estimation.measurements.gnss.Phase;
import org.orekit.frames.Transform;
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 phase measurements.
* @author David Soulard
* @since 10.2
*/
public class OnBoardAntennaPhaseModifier implements EstimationModifier<Phase> {
/** Position of the Antenna Phase Center in satellite frame. */
private final Vector3D antennaPhaseCenter;
/** Simple constructor.
* @param antennaPhaseCenter position of the Antenna Phase Center in satellite frame
*/
public OnBoardAntennaPhaseModifier(final Vector3D antennaPhaseCenter) {
this.antennaPhaseCenter = antennaPhaseCenter;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return Collections.emptyList();
}
/** {@inheritDoc} */
@Override
public void modify(final EstimatedMeasurement<Phase> estimated) {
// the participants are spacecraft at emission, ground station at reception
final TimeStampedPVCoordinates[] participants = estimated.getParticipants();
final AbsoluteDate emissionDate = participants[0].getDate();
final Vector3D pReception = participants[1].getPosition();
// transform from spacecraft to inertial frame at emission date
final SpacecraftState refState = estimated.getStates()[0];
final SpacecraftState emissionState = refState.shiftedBy(emissionDate.durationFrom(refState.getDate()));
final Transform spacecraftToInert = emissionState.toTransform().getInverse();
// compute the geometrical value of the 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 pSpacecraft = spacecraftToInert.transformPosition(Vector3D.ZERO);
final double rangeUsingSpacecraftCenter = Vector3D.distance(pSpacecraft, pReception);
// compute the geometrical value of the range replacing
// the spacecraft position with antenna phase center position
final Vector3D pAPC = spacecraftToInert.transformPosition(antennaPhaseCenter);
final double rangeUsingAntennaPhaseCenter = Vector3D.distance(pAPC, pReception);
// get the estimated value before this modifier is applied
final double[] value = estimated.getEstimatedValue();
// modify the value
value[0] += (rangeUsingAntennaPhaseCenter - rangeUsingSpacecraftCenter) / estimated.getObservedMeasurement().getWavelength();
estimated.setEstimatedValue(value);
}
}