AngularRaDec.java
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* CS licenses this file to You under the Apache License, Version 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.Arrays;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.MathUtils;
import org.orekit.frames.FieldStaticTransform;
import org.orekit.frames.Frame;
import org.orekit.frames.StaticTransform;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.TimeSpanMap.Span;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinates;
/** Class modeling a Right Ascension - Declination measurement from a ground point (station, telescope).
* The angles are given in an inertial reference frame.
* The motion of the spacecraft during the signal flight time is taken into
* account. The date of the measurement corresponds to the reception on
* ground of the reflected signal.
*
* @author Thierry Ceolin
* @author Maxime Journot
* @since 9.0
*/
public class AngularRaDec extends GroundReceiverMeasurement<AngularRaDec> {
/** Type of the measurement. */
public static final String MEASUREMENT_TYPE = "AngularRaDec";
/** Reference frame in which the right ascension - declination angles are given. */
private final Frame referenceFrame;
/** Simple constructor.
* @param station ground station from which measurement is performed
* @param referenceFrame Reference frame in which the right ascension - declination angles are given
* @param date date of the measurement
* @param angular observed value
* @param sigma theoretical standard deviation
* @param baseWeight base weight
* @param satellite satellite related to this measurement
* @since 9.3
*/
public AngularRaDec(final GroundStation station, final Frame referenceFrame, final AbsoluteDate date,
final double[] angular, final double[] sigma, final double[] baseWeight,
final ObservableSatellite satellite) {
super(station, false, date, angular, sigma, baseWeight, satellite);
this.referenceFrame = referenceFrame;
}
/** Get the reference frame in which the right ascension - declination angles are given.
* @return reference frame in which the right ascension - declination angles are given
*/
public Frame getReferenceFrame() {
return referenceFrame;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurementBase<AngularRaDec> theoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
final GroundReceiverCommonParametersWithoutDerivatives common = computeCommonParametersWithout(states[0]);
final TimeStampedPVCoordinates transitPV = common.getTransitPV();
// Station-satellite vector expressed in inertial frame
final Vector3D staSatInertial = transitPV.getPosition().subtract(common.getStationDownlink().getPosition());
// Field transform from inertial to reference frame at station's reception date
final StaticTransform inertialToReferenceDownlink = common.getState().getFrame().
getStaticTransformTo(referenceFrame, common.getStationDownlink().getDate());
// Station-satellite vector in reference frame
final Vector3D staSatReference = inertialToReferenceDownlink.transformVector(staSatInertial);
// Compute right ascension and declination
final double baseRightAscension = staSatReference.getAlpha();
final double twoPiWrap = MathUtils.normalizeAngle(baseRightAscension, getObservedValue()[0]) - baseRightAscension;
final double rightAscension = baseRightAscension + twoPiWrap;
final double declination = staSatReference.getDelta();
// Prepare the estimation
final EstimatedMeasurementBase<AngularRaDec> estimated =
new EstimatedMeasurementBase<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getTransitState()
}, new TimeStampedPVCoordinates[] {
transitPV,
common.getStationDownlink()
});
// azimuth - elevation values
estimated.setEstimatedValue(rightAscension, declination);
return estimated;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurement<AngularRaDec> theoreticalEvaluation(final int iteration, final int evaluation,
final SpacecraftState[] states) {
final SpacecraftState state = states[0];
// Right Ascension/elevation (in reference frame )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 (clock offset, station offsets, pole, prime meridian...)
final GroundReceiverCommonParametersWithDerivatives common = computeCommonParametersWithDerivatives(state);
final TimeStampedFieldPVCoordinates<Gradient> transitPV = common.getTransitPV();
// Station-satellite vector expressed in inertial frame
final FieldVector3D<Gradient> staSatInertial = transitPV.getPosition().subtract(common.getStationDownlink().getPosition());
// Field transform from inertial to reference frame at station's reception date
final FieldStaticTransform<Gradient> inertialToReferenceDownlink =
state.getFrame().getStaticTransformTo(referenceFrame, common.getStationDownlink().getDate());
// Station-satellite vector in reference frame
final FieldVector3D<Gradient> staSatReference = inertialToReferenceDownlink.transformVector(staSatInertial);
// Compute right ascension and declination
final Gradient baseRightAscension = staSatReference.getAlpha();
final double twoPiWrap = MathUtils.normalizeAngle(baseRightAscension.getReal(),
getObservedValue()[0]) - baseRightAscension.getReal();
final Gradient rightAscension = baseRightAscension.add(twoPiWrap);
final Gradient declination = staSatReference.getDelta();
// Prepare the estimation
final EstimatedMeasurement<AngularRaDec> estimated =
new EstimatedMeasurement<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getTransitState()
}, new TimeStampedPVCoordinates[] {
transitPV.toTimeStampedPVCoordinates(),
common.getStationDownlink().toTimeStampedPVCoordinates()
});
// azimuth - elevation values
estimated.setEstimatedValue(rightAscension.getValue(), declination.getValue());
// Partial derivatives of right ascension/declination in reference frame with respect to state
final double[] raDerivatives = rightAscension.getGradient();
final double[] decDerivatives = declination.getGradient();
estimated.setStateDerivatives(0,
Arrays.copyOfRange(raDerivatives, 0, 6), Arrays.copyOfRange(decDerivatives, 0, 6));
// Partial derivatives with respect to parameters
for (final ParameterDriver driver : getParametersDrivers()) {
for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
final Integer index = common.getIndices().get(span.getData());
if (index != null) {
estimated.setParameterDerivatives(driver, span.getStart(), raDerivatives[index], decDerivatives[index]);
}
}
}
return estimated;
}
/** Calculate the Line Of Sight of the given measurement.
* @param outputFrame output frame of the line of sight vector
* @return Vector3D the line of Sight of the measurement
* @since 12.0
*/
public Vector3D getObservedLineOfSight(final Frame outputFrame) {
return referenceFrame.getStaticTransformTo(outputFrame, getDate())
.transformVector(new Vector3D(getObservedValue()[0], getObservedValue()[1]));
}
}