AngularSeparationDetector.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
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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.propagation.events;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.ode.events.Action;
import org.orekit.bodies.CelestialBodies;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnDecreasing;
import org.orekit.utils.PVCoordinates;
import org.orekit.utils.PVCoordinatesProvider;
/** Detects when spacecraft comes close to a moving beacon, as seen from a moving observer.
* <p>The main use case for this detector is when the observer is in fact a ground
* station, modeled as a {@link org.orekit.frames.TopocentricFrame} and when the beacon
* is the {@link CelestialBodies#getSun() Sun}, for computing
* interferences for the telemetry link. Another similar case is when the beacon is
* another spacecraft, for interferences computation.</p>
* <p>The default handler behavior is to {@link Action#STOP stop}
* propagation when spacecraft enters the proximity zone. This can be changed by calling
* {@link #withHandler(EventHandler)} after construction.</p>
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @author Luc Maisonobe
* @since 8.0
*/
public class AngularSeparationDetector extends AbstractDetector<AngularSeparationDetector> {
/** Beacon at the center of the proximity zone. */
private final PVCoordinatesProvider beacon;
/** Observer for the spacecraft, that may also see the beacon at the same time if they are too close. */
private final PVCoordinatesProvider observer;
/** Proximity angle (rad). */
private final double proximityAngle;
/** Build a new angular separation detector.
* @param beacon beacon at the center of the proximity zone
* @param observer observer for the spacecraft, that may also see
* the beacon at the same time if they are too close to each other
* @param proximityAngle proximity angle as seen from observer, at which events are triggered (rad)
*/
public AngularSeparationDetector(final PVCoordinatesProvider beacon,
final PVCoordinatesProvider observer,
final double proximityAngle) {
this(60.0, 1.0e-3, 100, new StopOnDecreasing<AngularSeparationDetector>(),
beacon, observer, proximityAngle);
}
/** 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 beacon beacon at the center of the proximity zone
* @param observer observer for the spacecraft, that may also see
* the beacon at the same time if they are too close to each other
* @param proximityAngle proximity angle as seen from observer, at which events are triggered (rad)
*/
private AngularSeparationDetector(final double maxCheck, final double threshold,
final int maxIter,
final EventHandler<? super AngularSeparationDetector> handler,
final PVCoordinatesProvider beacon,
final PVCoordinatesProvider observer,
final double proximityAngle) {
super(maxCheck, threshold, maxIter, handler);
this.beacon = beacon;
this.observer = observer;
this.proximityAngle = proximityAngle;
}
/** {@inheritDoc} */
@Override
protected AngularSeparationDetector create(final double newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler<? super AngularSeparationDetector> newHandler) {
return new AngularSeparationDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
beacon, observer, proximityAngle);
}
/** Get the beacon at the center of the proximity zone.
* @return beacon at the center of the proximity zone
*/
public PVCoordinatesProvider getBeacon() {
return beacon;
}
/** Get the observer for the spacecraft.
* @return observer for the spacecraft
*/
public PVCoordinatesProvider getObserver() {
return observer;
}
/** Get the proximity angle (rad).
* @return the proximity angle
*/
public double getProximityAngle() {
return proximityAngle;
}
/** Compute the value of the switching function.
* <p>
* This function measures the angular separation between beacon and spacecraft
* as seen from the observer minus the proximity angle. It therefore triggers
* decreasing events when the spacecraft enters the proximity zone and increasing
* events when it leaves the proximity zone.
* </p>
* <p>
* No shadowing effect is taken into account, so this method is computed and
* may trigger events even when the spacecraft is below horizon for an observer
* which is a ground station. If such effects must be taken into account the
* detector must be associated with a {@link EventEnablingPredicateFilter predicate
* filter} where the {@link EnablingPredicate predicate function} is based on elevation.
* </p>
* @param s the current state information: date, kinematics, attitude
* @return value of the switching function
*/
public double g(final SpacecraftState s) {
final PVCoordinates sPV = s.getPVCoordinates();
final PVCoordinates bPV = beacon.getPVCoordinates(s.getDate(), s.getFrame());
final PVCoordinates oPV = observer.getPVCoordinates(s.getDate(), s.getFrame());
final double separation = Vector3D.angle(sPV.getPosition().subtract(oPV.getPosition()),
bPV.getPosition().subtract(oPV.getPosition()));
return separation - proximityAngle;
}
}