AlignmentDetector.java
/* Copyright 2002-2021 CS GROUP
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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
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* 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.propagation.events;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.ode.events.Action;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.SinCos;
import org.orekit.orbits.Orbit;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnIncreasing;
import org.orekit.utils.PVCoordinates;
import org.orekit.utils.PVCoordinatesProvider;
/** Finder for satellite/body alignment events in orbital plane.
* <p>This class finds alignment events.</p>
* <p>Alignment means the conjunction, with some threshold angle, between the satellite
* position and the projection in the orbital plane of some body position.</p>
* <p>The default handler behavior is to {@link Action#STOP stop}
* propagation when alignment is reached. This can be changed by calling
* {@link #withHandler(EventHandler)} after construction.</p>
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @author Pascal Parraud
*/
public class AlignmentDetector extends AbstractDetector<AlignmentDetector> {
/** Body to align. */
private final PVCoordinatesProvider body;
/** Alignment angle (rad). */
private final double alignAngle;
/** Cosinus of alignment angle. */
private final double cosAlignAngle;
/** Sinus of alignment angle. */
private final double sinAlignAngle;
/** Build a new alignment detector.
* <p>The orbit is used only to set an upper bound for the max check interval
* to period/3 and to set the convergence threshold according to orbit size.</p>
* @param orbit initial orbit
* @param body the body to align
* @param alignAngle the alignment angle (rad)
*/
public AlignmentDetector(final Orbit orbit,
final PVCoordinatesProvider body,
final double alignAngle) {
this(1.0e-13 * orbit.getKeplerianPeriod(), orbit, body, alignAngle);
}
/** Build a new alignment detector.
* @param maxCheck maximum checking interval (s)
* @param threshold convergence threshold (s)
* @param body the body to align
* @param alignAngle the alignment angle (rad)
*/
public AlignmentDetector(final double maxCheck, final double threshold,
final PVCoordinatesProvider body,
final double alignAngle) {
this(maxCheck, threshold, DEFAULT_MAX_ITER,
new StopOnIncreasing<AlignmentDetector>(),
body, alignAngle);
}
/** Build a new alignment detector.
* <p>The orbit is used only to set an upper bound for the max check interval
* to period/3.</p>
* @param threshold convergence threshold (s)
* @param orbit initial orbit
* @param body the body to align
* @param alignAngle the alignment angle (rad)
*/
public AlignmentDetector(final double threshold,
final Orbit orbit,
final PVCoordinatesProvider body,
final double alignAngle) {
this(orbit.getKeplerianPeriod() / 3, threshold, body, alignAngle);
}
/** Private constructor with full parameters.
* <p>
* This constructor is private as users are expected to use the builder
* API with the various {@code withXxx()} methods to set up the instance
* in a readable manner without using a huge amount of parameters.
* </p>
* @param maxCheck maximum checking interval (s)
* @param threshold convergence threshold (s)
* @param maxIter maximum number of iterations in the event time search
* @param handler event handler to call at event occurrences
* @param body the body to align
* @param alignAngle the alignment angle (rad)
*/
private AlignmentDetector(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<? super AlignmentDetector> handler,
final PVCoordinatesProvider body,
final double alignAngle) {
super(maxCheck, threshold, maxIter, handler);
final SinCos sc = FastMath.sinCos(alignAngle);
this.body = body;
this.alignAngle = alignAngle;
this.cosAlignAngle = sc.cos();
this.sinAlignAngle = sc.sin();
}
/** {@inheritDoc} */
@Override
protected AlignmentDetector create(final double newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler<? super AlignmentDetector> newHandler) {
return new AlignmentDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
body, alignAngle);
}
/** Get the body to align.
* @return the body to align
*/
public PVCoordinatesProvider getPVCoordinatesProvider() {
return body;
}
/** Get the alignment angle (rad).
* @return the alignment angle
*/
public double getAlignAngle() {
return alignAngle;
}
/** Compute the value of the switching function.
* This function measures the difference between the alignment angle and the
* angle between the satellite position and the body position projection in the
* orbital plane.
* @param s the current state information: date, kinematics, attitude
* @return value of the switching function
*/
public double g(final SpacecraftState s) {
final PVCoordinates pv = s.getPVCoordinates();
final Vector3D a = pv.getPosition().normalize();
final Vector3D b = Vector3D.crossProduct(pv.getMomentum(), a).normalize();
final Vector3D x = new Vector3D(cosAlignAngle, a, sinAlignAngle, b);
final Vector3D y = new Vector3D(sinAlignAngle, a, -cosAlignAngle, b);
final Vector3D pb = body.getPVCoordinates(s.getDate(), s.getFrame()).getPosition();
final double beta = FastMath.atan2(Vector3D.dotProduct(pb, y), Vector3D.dotProduct(pb, x));
final double betm = -FastMath.PI - beta;
final double betp = FastMath.PI - beta;
if (beta < betm) {
return betm;
} else if (beta < betp) {
return beta;
} else {
return betp;
}
}
}