NadirPointing.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.attitudes;
import java.util.ArrayList;
import java.util.List;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.bodies.BodyShape;
import org.orekit.bodies.FieldGeodeticPoint;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.frames.FieldStaticTransform;
import org.orekit.frames.FieldTransform;
import org.orekit.frames.Frame;
import org.orekit.frames.StaticTransform;
import org.orekit.frames.Transform;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.time.FieldTimeInterpolator;
import org.orekit.time.TimeInterpolator;
import org.orekit.utils.CartesianDerivativesFilter;
import org.orekit.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.PVCoordinatesProvider;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
import org.orekit.utils.TimeStampedFieldPVCoordinatesHermiteInterpolator;
import org.orekit.utils.TimeStampedPVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinatesHermiteInterpolator;
/**
* This class handles nadir pointing attitude provider.
* <p>
* This class represents the attitude provider where the satellite z axis is
* pointing to the vertical of the ground point under satellite.</p>
* <p>
* The object <code>NadirPointing</code> is guaranteed to be immutable.
* </p>
* @see GroundPointing
* @author Véronique Pommier-Maurussane
*/
public class NadirPointing extends GroundPointing {
/** Body shape. */
private final BodyShape shape;
/** Creates new instance.
* @param inertialFrame frame in which orbital velocities are computed
* @param shape Body shape
* @since 7.1
*/
public NadirPointing(final Frame inertialFrame, final BodyShape shape) {
// Call constructor of superclass
super(inertialFrame, shape.getBodyFrame());
this.shape = shape;
}
/** {@inheritDoc} */
public TimeStampedPVCoordinates getTargetPV(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame) {
// transform from specified reference frame to body frame
final Transform refToBody = frame.getTransformTo(shape.getBodyFrame(), date);
// sample intersection points in current date neighborhood
final double h = 0.01;
final List<TimeStampedPVCoordinates> sample = new ArrayList<>();
sample.add(nadirRef(pvProv.getPVCoordinates(date.shiftedBy(-2 * h), frame), refToBody.staticShiftedBy(-2 * h)));
sample.add(nadirRef(pvProv.getPVCoordinates(date.shiftedBy(-h), frame), refToBody.staticShiftedBy(-h)));
sample.add(nadirRef(pvProv.getPVCoordinates(date, frame), refToBody));
sample.add(nadirRef(pvProv.getPVCoordinates(date.shiftedBy(+h), frame), refToBody.staticShiftedBy(+h)));
sample.add(nadirRef(pvProv.getPVCoordinates(date.shiftedBy(+2 * h), frame), refToBody.staticShiftedBy(+2 * h)));
// create interpolator
final TimeInterpolator<TimeStampedPVCoordinates> interpolator =
new TimeStampedPVCoordinatesHermiteInterpolator(sample.size(), CartesianDerivativesFilter.USE_P);
// use interpolation to compute properly the time-derivatives
return interpolator.interpolate(date, sample);
}
/** {@inheritDoc} */
public <T extends CalculusFieldElement<T>> TimeStampedFieldPVCoordinates<T> getTargetPV(final FieldPVCoordinatesProvider<T> pvProv,
final FieldAbsoluteDate<T> date,
final Frame frame) {
// zero
final T zero = date.getField().getZero();
// transform from specified reference frame to body frame
final FieldTransform<T> refToBody = frame.getTransformTo(shape.getBodyFrame(), date);
// sample intersection points in current date neighborhood
final double h = 0.01;
final List<TimeStampedFieldPVCoordinates<T>> sample = new ArrayList<>();
sample.add(nadirRef(pvProv.getPVCoordinates(date.shiftedBy(-2 * h), frame), refToBody.staticShiftedBy(zero.add(-2 * h))));
sample.add(nadirRef(pvProv.getPVCoordinates(date.shiftedBy(-h), frame), refToBody.staticShiftedBy(zero.add(-h))));
sample.add(nadirRef(pvProv.getPVCoordinates(date, frame), refToBody));
sample.add(nadirRef(pvProv.getPVCoordinates(date.shiftedBy(+h), frame), refToBody.staticShiftedBy(zero.add(+h))));
sample.add(nadirRef(pvProv.getPVCoordinates(date.shiftedBy(+2 * h), frame), refToBody.staticShiftedBy(zero.add(+2 * h))));
// create interpolator
final FieldTimeInterpolator<TimeStampedFieldPVCoordinates<T>, T> interpolator =
new TimeStampedFieldPVCoordinatesHermiteInterpolator<>(sample.size(), CartesianDerivativesFilter.USE_P);
// use interpolation to compute properly the time-derivatives
return interpolator.interpolate(date, sample);
}
/** Compute ground point in nadir direction, in reference frame.
* @param scRef spacecraft coordinates in reference frame
* @param refToBody transform from reference frame to body frame
* @return intersection point in body frame (only the position is set!)
*/
private TimeStampedPVCoordinates nadirRef(final TimeStampedPVCoordinates scRef,
final StaticTransform refToBody) {
final Vector3D satInBodyFrame = refToBody.transformPosition(scRef.getPosition());
// satellite position in geodetic coordinates
final GeodeticPoint gpSat = shape.transform(satInBodyFrame, getBodyFrame(), scRef.getDate());
// nadir position in geodetic coordinates
final GeodeticPoint gpNadir = new GeodeticPoint(gpSat.getLatitude(), gpSat.getLongitude(), 0.0);
// nadir point position in body frame
final Vector3D pNadirBody = shape.transform(gpNadir);
// nadir point position in reference frame
final Vector3D pNadirRef = refToBody.getInverse().transformPosition(pNadirBody);
return new TimeStampedPVCoordinates(scRef.getDate(), pNadirRef, Vector3D.ZERO, Vector3D.ZERO);
}
/** Compute ground point in nadir direction, in reference frame.
* @param scRef spacecraft coordinates in reference frame
* @param refToBody transform from reference frame to body frame
* @param <T> type of the field elements
* @return intersection point in body frame (only the position is set!)
* @since 9.0
*/
private <T extends CalculusFieldElement<T>> TimeStampedFieldPVCoordinates<T> nadirRef(final TimeStampedFieldPVCoordinates<T> scRef,
final FieldStaticTransform<T> refToBody) {
final FieldVector3D<T> satInBodyFrame = refToBody.transformPosition(scRef.getPosition());
// satellite position in geodetic coordinates
final FieldGeodeticPoint<T> gpSat = shape.transform(satInBodyFrame, getBodyFrame(), scRef.getDate());
// nadir position in geodetic coordinates
final FieldGeodeticPoint<T> gpNadir = new FieldGeodeticPoint<>(gpSat.getLatitude(), gpSat.getLongitude(),
gpSat.getAltitude().getField().getZero());
// nadir point position in body frame
final FieldVector3D<T> pNadirBody = shape.transform(gpNadir);
// nadir point position in reference frame
final FieldVector3D<T> pNadirRef = refToBody.getInverse().transformPosition(pNadirBody);
final FieldVector3D<T> zero = FieldVector3D.getZero(gpSat.getAltitude().getField());
return new TimeStampedFieldPVCoordinates<>(scRef.getDate(), pNadirRef, zero, zero);
}
}