EventEnablingPredicateFilter.java
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* 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.propagation.events;
import java.util.Arrays;
import org.hipparchus.ode.events.Action;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.time.AbsoluteDate;
/** Wrapper used to detect events only when enabled by an external predicated function.
*
* <p>General {@link EventDetector events} are defined implicitly
* by a {@link EventDetector#g(SpacecraftState) g function} crossing
* zero. This implies that during an orbit propagation, events are
* triggered at all zero crossings.
* </p>
*
* <p>Sometimes, users would like to enable or disable events by themselves,
* for example to trigger them only for certain orbits, or to check elevation
* maximums only when elevation itself is positive (i.e. they want to
* discard elevation maximums below ground). In these cases, looking precisely
* for all events location and triggering events that will later be ignored
* is a waste of computing time.</p>
*
* <p>Users can wrap a regular {@link EventDetector event detector} in
* an instance of this class and provide this wrapping instance to
* a {@link org.orekit.propagation.Propagator}
* in order to avoid wasting time looking for uninteresting events.
* The wrapper will intercept the calls to the {@link
* EventDetector#g(SpacecraftState) g function} and to the {@link
* EventDetector#eventOccurred(SpacecraftState, boolean)
* eventOccurred} method in order to ignore uninteresting events. The
* wrapped regular {@link EventDetector event detector} will the see only
* the interesting events, i.e. either only events that occur when a
* user-provided event enabling predicate function is true, ignoring all events
* that occur when the event enabling predicate function is false. The number of
* calls to the {@link EventDetector#g(SpacecraftState) g function} will also be
* reduced.</p>
* @see EventSlopeFilter
* @since 7.1
*/
public class EventEnablingPredicateFilter<T extends EventDetector>
extends AbstractDetector<EventEnablingPredicateFilter<T>> {
/** Number of past transformers updates stored. */
private static final int HISTORY_SIZE = 100;
/** Wrapped event detector. */
private final T rawDetector;
/** Enabling predicate function. */
private final EnablingPredicate<? super T> enabler;
/** Transformers of the g function. */
private final Transformer[] transformers;
/** Update time of the transformers. */
private final AbsoluteDate[] updates;
/** Indicator for forward integration. */
private boolean forward;
/** Extreme time encountered so far. */
private AbsoluteDate extremeT;
/** Detector function value at extremeT. */
private double extremeG;
/** Wrap an {@link EventDetector event detector}.
* @param rawDetector event detector to wrap
* @param enabler event enabling predicate function to use
*/
public EventEnablingPredicateFilter(final T rawDetector,
final EnablingPredicate<? super T> enabler) {
this(rawDetector.getMaxCheckInterval(), rawDetector.getThreshold(),
rawDetector.getMaxIterationCount(), new LocalHandler<T>(),
rawDetector, enabler);
}
/** 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 rawDetector event detector to wrap
* @param enabler event enabling function to use
*/
private EventEnablingPredicateFilter(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<? super EventEnablingPredicateFilter<T>> handler,
final T rawDetector,
final EnablingPredicate<? super T> enabler) {
super(maxCheck, threshold, maxIter, handler);
this.rawDetector = rawDetector;
this.enabler = enabler;
this.transformers = new Transformer[HISTORY_SIZE];
this.updates = new AbsoluteDate[HISTORY_SIZE];
}
/** {@inheritDoc} */
@Override
protected EventEnablingPredicateFilter<T> create(final double newMaxCheck, final double newThreshold,
final int newMaxIter,
final EventHandler<? super EventEnablingPredicateFilter<T>> newHandler) {
return new EventEnablingPredicateFilter<T>(newMaxCheck, newThreshold, newMaxIter, newHandler, rawDetector, enabler);
}
/** {@inheritDoc} */
public void init(final SpacecraftState s0,
final AbsoluteDate t) {
super.init(s0, t);
// delegate to raw detector
rawDetector.init(s0, t);
// initialize events triggering logic
forward = t.compareTo(s0.getDate()) >= 0;
extremeT = forward ? AbsoluteDate.PAST_INFINITY : AbsoluteDate.FUTURE_INFINITY;
extremeG = Double.NaN;
Arrays.fill(transformers, Transformer.UNINITIALIZED);
Arrays.fill(updates, extremeT);
}
/** {@inheritDoc} */
public double g(final SpacecraftState s) {
final double rawG = rawDetector.g(s);
final boolean isEnabled = enabler.eventIsEnabled(s, rawDetector, rawG);
if (Double.isNaN(extremeG)) {
extremeG = rawG;
}
// search which transformer should be applied to g
if (forward) {
final int last = transformers.length - 1;
if (extremeT.compareTo(s.getDate()) < 0) {
// we are at the forward end of the history
// check if enabled status has changed
final Transformer previous = transformers[last];
final Transformer next = selectTransformer(previous, extremeG, isEnabled);
if (next != previous) {
// there is a status change somewhere between extremeT and t.
// the new transformer is valid for t (this is how we have just computed
// it above), but it is in fact valid on both sides of the change, so
// it was already valid before t and even up to previous time. We store
// the switch at extremeT for safety, to ensure the previous transformer
// is not applied too close of the root
System.arraycopy(updates, 1, updates, 0, last);
System.arraycopy(transformers, 1, transformers, 0, last);
updates[last] = extremeT;
transformers[last] = next;
}
extremeT = s.getDate();
extremeG = rawG;
// apply the transform
return next.transformed(rawG);
} else {
// we are in the middle of the history
// select the transformer
for (int i = last; i > 0; --i) {
if (updates[i].compareTo(s.getDate()) <= 0) {
// apply the transform
return transformers[i].transformed(rawG);
}
}
return transformers[0].transformed(rawG);
}
} else {
if (s.getDate().compareTo(extremeT) < 0) {
// we are at the backward end of the history
// check if a new rough root has been crossed
final Transformer previous = transformers[0];
final Transformer next = selectTransformer(previous, extremeG, isEnabled);
if (next != previous) {
// there is a status change somewhere between extremeT and t.
// the new transformer is valid for t (this is how we have just computed
// it above), but it is in fact valid on both sides of the change, so
// it was already valid before t and even up to previous time. We store
// the switch at extremeT for safety, to ensure the previous transformer
// is not applied too close of the root
System.arraycopy(updates, 0, updates, 1, updates.length - 1);
System.arraycopy(transformers, 0, transformers, 1, transformers.length - 1);
updates[0] = extremeT;
transformers[0] = next;
}
extremeT = s.getDate();
extremeG = rawG;
// apply the transform
return next.transformed(rawG);
} else {
// we are in the middle of the history
// select the transformer
for (int i = 0; i < updates.length - 1; ++i) {
if (s.getDate().compareTo(updates[i]) <= 0) {
// apply the transform
return transformers[i].transformed(rawG);
}
}
return transformers[updates.length - 1].transformed(rawG);
}
}
}
/** Get next function transformer in the specified direction.
* @param previous transformer active on the previous point with respect
* to integration direction (may be null if no previous point is known)
* @param previousG value of the g function at the previous point
* @param isEnabled if true the event should be enabled now
* @return next transformer transformer
*/
private Transformer selectTransformer(final Transformer previous, final double previousG, final boolean isEnabled) {
if (isEnabled) {
// we need to select a transformer that can produce zero crossings,
// so it is either Transformer.PLUS or Transformer.MINUS
switch (previous) {
case UNINITIALIZED :
return Transformer.PLUS; // this initial choice is arbitrary, it could have been Transformer.MINUS
case MIN :
return previousG >= 0 ? Transformer.MINUS : Transformer.PLUS;
case MAX :
return previousG >= 0 ? Transformer.PLUS : Transformer.MINUS;
default :
return previous;
}
} else {
// we need to select a transformer that cannot produce any zero crossings,
// so it is either Transformer.MAX or Transformer.MIN
switch (previous) {
case UNINITIALIZED :
return Transformer.MAX; // this initial choice is arbitrary, it could have been Transformer.MIN
case PLUS :
return previousG >= 0 ? Transformer.MAX : Transformer.MIN;
case MINUS :
return previousG >= 0 ? Transformer.MIN : Transformer.MAX;
default :
return previous;
}
}
}
/** Local handler. */
private static class LocalHandler<T extends EventDetector> implements EventHandler<EventEnablingPredicateFilter<T>> {
/** {@inheritDoc} */
public Action eventOccurred(final SpacecraftState s, final EventEnablingPredicateFilter<T> ef, final boolean increasing) {
final Transformer transformer = ef.forward ? ef.transformers[ef.transformers.length - 1] : ef.transformers[0];
return ef.rawDetector.eventOccurred(s, transformer == Transformer.PLUS ? increasing : !increasing);
}
/** {@inheritDoc} */
@Override
public SpacecraftState resetState(final EventEnablingPredicateFilter<T> ef, final SpacecraftState oldState) {
return ef.rawDetector.resetState(oldState);
}
}
}