ExtremumApproachDetector.java
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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.propagation.PropagatorsParallelizer;
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 extremum approach events.
* <p>
* This class finds extremum approach events (i.e. closest or farthest approach).
* </p>
* <p>
* The default implementation behavior is to {@link Action#CONTINUE continue} propagation at farthest approach and to
* {@link Action#STOP stop} propagation at closest approach. This can be changed by calling
* {@link #withHandler(EventHandler)} after construction (go to the end of the documentation to see an example).
* </p>
* <p>
* As this detector needs two objects (moving relative to each other), it embeds one
* {@link PVCoordinatesProvider coordinates provider} for the secondary object and is registered as an event detector in
* the propagator of the primary object. The secondary object {@link PVCoordinatesProvider coordinates provider} will
* therefore be driven by this detector (and hence by the propagator in which this detector is registered).
* </p>
* <p><b>
* In order to avoid infinite recursion, care must be taken to have the secondary object provider being <em>completely
* independent</em> from anything else. In particular, if the provider is a propagator, it should <em>not</em> be run
* together in a {@link PropagatorsParallelizer propagators parallelizer} with the propagator this detector is
* registered in. It is fine however to configure two separate propagators PsA and PsB with similar settings for the
* secondary object and one propagator Pm for the primary object and then use Psa in this detector registered within Pm
* while Pm and Psb are run in the context of a {@link PropagatorsParallelizer propagators parallelizer}.
* </b></p>
* <p>
* For efficiency reason during the event search loop, it is recommended to have the secondary provider be an analytical
* propagator or an ephemeris. A numerical propagator as a secondary propagator works but is expected to be
* computationally costly.
* </p>
* <p>
* Also, it is possible to detect solely one type of event using an {@link EventSlopeFilter event slope filter}. For
* example in order to only detect closest approach, one should type the following :
* </p>
* <pre>{@code
* ExtremumApproachDetector extremumApproachDetector = new ExtremumApproachDetector(secondaryPVProvider);
* EventDetector closeApproachDetector = new EventSlopeFilter<ExtremumApproachDetector>(extremumApproachDetector,FilterType.TRIGGER_ONLY_INCREASING_EVENTS);
* }
* </pre>
*
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @see EventSlopeFilter
* @see FilterType
* @author Vincent Cucchietti
* @since 11.3
*/
public class ExtremumApproachDetector extends AbstractDetector<ExtremumApproachDetector> {
/**
* PVCoordinates provider of the other object with which we want to find out the extremum approach.
*/
private final PVCoordinatesProvider secondaryPVProvider;
/**
* Constructor with default values.
* <p>
* By default, the implemented behavior is to {@link Action#CONTINUE continue} propagation at farthest approach and
* to {@link Action#STOP stop} propagation at closest approach.
* </p>
*
* @param secondaryPVProvider PVCoordinates provider of the other object with which we want to find out the extremum
* approach.
*/
public ExtremumApproachDetector(final PVCoordinatesProvider secondaryPVProvider) {
this(AdaptableInterval.of(DEFAULT_MAXCHECK), DEFAULT_THRESHOLD, DEFAULT_MAX_ITER, new StopOnIncreasing(), secondaryPVProvider);
}
/**
* Constructor.
* <p>
* This constructor is to be used if the user wants to change the default behavior of the detector.
* </p>
*
* @param maxCheck Maximum checking interval.
* @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 secondaryPVProvider PVCoordinates provider of the other object with which we want to find out the extremum
* approach.
* @see EventHandler
*/
protected ExtremumApproachDetector(final AdaptableInterval maxCheck, final double threshold, final int maxIter,
final EventHandler handler, final PVCoordinatesProvider secondaryPVProvider) {
super(maxCheck, threshold, maxIter, handler);
this.secondaryPVProvider = secondaryPVProvider;
}
/**
* The {@code g} is positive when the primary object is getting further away from the secondary object and is
* negative when it is getting closer to it.
*
* @param s the current state information: date, kinematics, attitude
* @return value of the switching function
*/
public double g(final SpacecraftState s) {
final PVCoordinates deltaPV = computeDeltaPV(s);
return Vector3D.dotProduct(deltaPV.getPosition(), deltaPV.getVelocity());
}
/**
* Compute the relative PV between primary and secondary objects.
*
* @param s Spacecraft state.
* @return Relative position between primary (=s) and secondaryPVProvider.
*/
public PVCoordinates computeDeltaPV(final SpacecraftState s) {
return new PVCoordinates(s.getPVCoordinates(),
secondaryPVProvider.getPVCoordinates(s.getDate(), s.getFrame()));
}
/** {@inheritDoc} */
@Override
protected ExtremumApproachDetector create(final AdaptableInterval newMaxCheck, final double newThreshold, final int newMaxIter,
final EventHandler newHandler) {
return new ExtremumApproachDetector(newMaxCheck, newThreshold, newMaxIter, newHandler, secondaryPVProvider);
}
/**
* Get the secondary position-velocity provider stored in this instance.
*
* @return the secondary position-velocity provider stored in this instance
*/
public PVCoordinatesProvider getSecondaryPVProvider() {
return secondaryPVProvider;
}
}