AngularAzEl.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.analysis.differentiation.GradientField;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathUtils;
import org.orekit.frames.Frame;
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 an Azimuth-Elevation measurement from a ground station.
* 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
* @since 8.0
*/
public class AngularAzEl extends GroundReceiverMeasurement<AngularAzEl> {
/** Type of the measurement. */
public static final String MEASUREMENT_TYPE = "AngularAzEl";
/** Simple constructor.
* @param station ground station from which measurement is performed
* @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 AngularAzEl(final GroundStation station, final AbsoluteDate date,
final double[] angular, final double[] sigma, final double[] baseWeight,
final ObservableSatellite satellite) {
super(station, false, date, angular, sigma, baseWeight, satellite);
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurementBase<AngularAzEl> theoreticalEvaluationWithoutDerivatives(final int iteration,
final int evaluation,
final SpacecraftState[] states) {
final GroundReceiverCommonParametersWithoutDerivatives common = computeCommonParametersWithout(states[0]);
final TimeStampedPVCoordinates transitPV = common.getTransitPV();
// Station topocentric frame (east-north-zenith) in inertial frame expressed as Gradient
final Vector3D east = common.getOffsetToInertialDownlink().transformVector(Vector3D.PLUS_I);
final Vector3D north = common.getOffsetToInertialDownlink().transformVector(Vector3D.PLUS_J);
final Vector3D zenith = common.getOffsetToInertialDownlink().transformVector(Vector3D.PLUS_K);
// Station-satellite vector expressed in inertial frame
final Vector3D staSat = transitPV.getPosition().subtract(common.getStationDownlink().getPosition());
// Compute azimuth/elevation
final double baseAzimuth = FastMath.atan2(staSat.dotProduct(east), staSat.dotProduct(north));
final double twoPiWrap = MathUtils.normalizeAngle(baseAzimuth, getObservedValue()[0]) - baseAzimuth;
final double azimuth = baseAzimuth + twoPiWrap;
final double elevation = FastMath.asin(staSat.dotProduct(zenith) / staSat.getNorm());
// Prepare the estimation
final EstimatedMeasurementBase<AngularAzEl> estimated =
new EstimatedMeasurementBase<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getTransitState()
}, new TimeStampedPVCoordinates[] {
transitPV,
common.getStationDownlink()
});
// azimuth - elevation values
estimated.setEstimatedValue(azimuth, elevation);
return estimated;
}
/** {@inheritDoc} */
@Override
protected EstimatedMeasurement<AngularAzEl> theoreticalEvaluation(final int iteration, final int evaluation,
final SpacecraftState[] states) {
final SpacecraftState state = states[0];
// Azimuth/elevation 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 topocentric frame (east-north-zenith) in inertial frame expressed as Gradient
final GradientField field = common.getTauD().getField();
final FieldVector3D<Gradient> east = common.getOffsetToInertialDownlink().transformVector(FieldVector3D.getPlusI(field));
final FieldVector3D<Gradient> north = common.getOffsetToInertialDownlink().transformVector(FieldVector3D.getPlusJ(field));
final FieldVector3D<Gradient> zenith = common.getOffsetToInertialDownlink().transformVector(FieldVector3D.getPlusK(field));
// Station-satellite vector expressed in inertial frame
final FieldVector3D<Gradient> staSat = transitPV.getPosition().subtract(common.getStationDownlink().getPosition());
// Compute azimuth/elevation
final Gradient baseAzimuth = staSat.dotProduct(east).atan2(staSat.dotProduct(north));
final double twoPiWrap = MathUtils.normalizeAngle(baseAzimuth.getReal(), getObservedValue()[0]) -
baseAzimuth.getReal();
final Gradient azimuth = baseAzimuth.add(twoPiWrap);
final Gradient elevation = staSat.dotProduct(zenith).divide(staSat.getNorm()).asin();
// Prepare the estimation
final EstimatedMeasurement<AngularAzEl> estimated =
new EstimatedMeasurement<>(this, iteration, evaluation,
new SpacecraftState[] {
common.getTransitState()
}, new TimeStampedPVCoordinates[] {
transitPV.toTimeStampedPVCoordinates(),
common.getStationDownlink().toTimeStampedPVCoordinates()
});
// azimuth - elevation values
estimated.setEstimatedValue(azimuth.getValue(), elevation.getValue());
// Partial derivatives of azimuth/elevation with respect to state
// (beware element at index 0 is the value, not a derivative)
final double[] azDerivatives = azimuth.getGradient();
final double[] elDerivatives = elevation.getGradient();
estimated.setStateDerivatives(0,
Arrays.copyOfRange(azDerivatives, 0, 6), Arrays.copyOfRange(elDerivatives, 0, 6));
// Set partial derivatives with respect to parameters
// (beware element at index 0 is the value, not a derivative)
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(), azDerivatives[index], elDerivatives[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
*/
public Vector3D getObservedLineOfSight(final Frame outputFrame) {
return getStation().getBaseFrame().getStaticTransformTo(outputFrame, getDate())
.transformVector(new Vector3D(MathUtils.SEMI_PI - getObservedValue()[0], getObservedValue()[1]));
}
}