FieldExtremumApproachDetector.java
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package org.orekit.propagation.events;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.Field;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.ode.events.Action;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.PropagatorsParallelizer;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.FieldEventHandler;
import org.orekit.propagation.events.handlers.FieldStopOnIncreasing;
import org.orekit.utils.FieldPVCoordinates;
import org.orekit.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.PVCoordinatesProvider;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinates;
/**
* 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 FieldAbstractDetector#withHandler(FieldEventHandler)} 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 FieldPVCoordinatesProvider fielded coordinates provider} for the secondary object and is registered as an event
* detector in the propagator of the primary object. The secondary object
* {@link FieldPVCoordinatesProvider fielded coordinates provider} will therefore be driven by this detector (and hence by
* the propagator in which this detector is registered). Note that you can also create this detector using a standard
* {@link PVCoordinatesProvider coordinates provider}
* </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
* FieldExtremumApproachDetector<Type> extremumApproachDetector = new FieldExtremumApproachDetector<>(field, secondaryPVProvider);
* FieldEventDetector<Type> closeApproachDetector = new FieldEventSlopeFilter<>(extremumApproachDetector, FilterType.TRIGGER_ONLY_INCREASING_EVENTS);
* }
* </pre>
*
* @author Vincent Cucchietti
* @see org.orekit.propagation.FieldPropagator#addEventDetector(FieldEventDetector)
* @see FieldEventSlopeFilter
* @see FilterType
* @since 11.3
*/
public class FieldExtremumApproachDetector<T extends CalculusFieldElement<T>>
extends FieldAbstractDetector<FieldExtremumApproachDetector<T>, T> {
/**
* PVCoordinates provider of the other object with which we want to find out the extremum approach.
*/
private final FieldPVCoordinatesProvider<T> 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>
* <b>BEWARE : This constructor will "fieldify" given secondary PV coordinates provider.</b>
*
* @param field field the type of number to use
* @param secondaryPVProvider PVCoordinates provider of the other object with which we want to find out the extremum
* approach.
*/
public FieldExtremumApproachDetector(final Field<T> field, final PVCoordinatesProvider secondaryPVProvider) {
this(field, (FieldPVCoordinatesProvider<T>) (date, frame) -> {
final TimeStampedPVCoordinates timeStampedPV =
secondaryPVProvider.getPVCoordinates(date.toAbsoluteDate(), frame);
return new TimeStampedFieldPVCoordinates<>(field, timeStampedPV);
});
}
/**
* 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 field field the type of number to use
* @param secondaryPVProvider PVCoordinates provider of the other object with which we want to find out the extremum
* approach.
*/
public FieldExtremumApproachDetector(final Field<T> field, final FieldPVCoordinatesProvider<T> secondaryPVProvider) {
this(field.getZero().newInstance(DEFAULT_MAXCHECK), field.getZero().newInstance(DEFAULT_THRESHOLD), DEFAULT_MAX_ITER,
new FieldStopOnIncreasing<>(), 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 FieldEventHandler
*/
protected FieldExtremumApproachDetector(final T maxCheck, final T threshold, final int maxIter,
final FieldEventHandler<T> handler,
final FieldPVCoordinatesProvider<T> secondaryPVProvider) {
this(FieldAdaptableInterval.of(maxCheck.getReal()), threshold, maxIter, handler, 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 FieldExtremumApproachDetector(final FieldAdaptableInterval<T> maxCheck, final T threshold, final int maxIter,
final FieldEventHandler<T> handler,
final FieldPVCoordinatesProvider<T> secondaryPVProvider) {
super(maxCheck, threshold, maxIter, handler);
this.secondaryPVProvider = secondaryPVProvider;
}
/**
* Compute the relative PV between primary and secondary objects.
*
* @param s Spacecraft state.
*
* @return Relative position between primary (=s) and secondaryPVProvider.
*
* @deprecated The output type of this method shall be modified in the future to improve code efficiency (though it will
* still give access to the relative position and velocity)
*/
@Deprecated
public FieldPVCoordinates<T> computeDeltaPV(final FieldSpacecraftState<T> s) {
final FieldVector3D<T> primaryPos = s.getPosition();
final FieldVector3D<T> primaryVel = s.getPVCoordinates().getVelocity();
final FieldPVCoordinates<T> secondaryPV = secondaryPVProvider.getPVCoordinates(s.getDate(), s.getFrame());
final FieldVector3D<T> secondaryPos = secondaryPV.getPosition();
final FieldVector3D<T> secondaryVel = secondaryPV.getVelocity();
final FieldVector3D<T> relativePos = secondaryPos.subtract(primaryPos);
final FieldVector3D<T> relativeVel = secondaryVel.subtract(primaryVel);
return new FieldPVCoordinates<>(relativePos, relativeVel);
}
/**
* Get the secondary position-velocity provider stored in this instance.
*
* @return the secondary position-velocity provider stored in this instance
*/
public FieldPVCoordinatesProvider<T> getSecondaryPVProvider() {
return 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
*/
@Override
public T g(final FieldSpacecraftState<T> s) {
final FieldPVCoordinates<T> deltaPV = computeDeltaPV(s);
return FieldVector3D.dotProduct(deltaPV.getPosition(), deltaPV.getVelocity());
}
/** {@inheritDoc} */
@Override
protected FieldExtremumApproachDetector<T> create(final FieldAdaptableInterval<T> newMaxCheck, final T newThreshold,
final int newMaxIter, final FieldEventHandler<T> newHandler) {
return new FieldExtremumApproachDetector<>(newMaxCheck, newThreshold, newMaxIter, newHandler, secondaryPVProvider);
}
}