EventSlopeFilter.java
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF 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
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
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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 only increasing or decreasing events.
*
* <p>This class is heavily based on the class EventFilter from the
* Hipparchus library. The changes performed consist in replacing
* raw types (double and double arrays) with space dynamics types
* ({@link AbsoluteDate}, {@link SpacecraftState}).</p>
*
* <p>General {@link EventDetector events} are defined implicitly
* by a {@link EventDetector#g(SpacecraftState) g function} crossing
* zero. This function needs to be continuous in the event neighborhood,
* and its sign must remain consistent between events. This implies that
* during an orbit propagation, events triggered are alternately events
* for which the function increases from negative to positive values,
* and events for which the function decreases from positive to
* negative values.
* </p>
*
* <p>Sometimes, users are only interested in one type of event (say
* increasing events for example) and not in the other type. 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 then see only
* the interesting events, i.e. either only {@code increasing} events or
* only {@code decreasing} events. The number of calls to the {@link
* EventDetector#g(SpacecraftState) g function} will also be reduced.</p>
* @see EventEnablingPredicateFilter
*/
public class EventSlopeFilter<T extends EventDetector> extends AbstractDetector<EventSlopeFilter<T>> {
/** Number of past transformers updates stored. */
private static final int HISTORY_SIZE = 100;
/** Wrapped event detector. */
private final T rawDetector;
/** Filter to use. */
private final FilterType filter;
/** 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;
/** Wrap an {@link EventDetector event detector}.
* @param rawDetector event detector to wrap
* @param filter filter to use
*/
public EventSlopeFilter(final T rawDetector, final FilterType filter) {
this(rawDetector.getMaxCheckInterval(), rawDetector.getThreshold(),
rawDetector.getMaxIterationCount(), new LocalHandler<T>(),
rawDetector, filter);
}
/** 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 filter filter to use
* @since 6.1
*/
private EventSlopeFilter(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<? super EventSlopeFilter<T>> handler,
final T rawDetector, final FilterType filter) {
super(maxCheck, threshold, maxIter, handler);
this.rawDetector = rawDetector;
this.filter = filter;
this.transformers = new Transformer[HISTORY_SIZE];
this.updates = new AbsoluteDate[HISTORY_SIZE];
}
/** {@inheritDoc} */
@Override
protected EventSlopeFilter<T> create(final double newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler<? super EventSlopeFilter<T>> newHandler) {
return new EventSlopeFilter<T>(newMaxCheck, newThreshold, newMaxIter, newHandler, rawDetector, filter);
}
/**
* Get the wrapped raw detector.
* @return the wrapped raw detector
* @since 11.1
*/
public EventDetector getDetector() {
return rawDetector;
}
/** {@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;
Arrays.fill(transformers, Transformer.UNINITIALIZED);
Arrays.fill(updates, extremeT);
}
/** {@inheritDoc} */
public double g(final SpacecraftState s) {
final double rawG = rawDetector.g(s);
// 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 a new rough root has been crossed
final Transformer previous = transformers[last];
final Transformer next = filter.selectTransformer(previous, rawG, forward);
if (next != previous) {
// there is a root 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 root, 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();
// 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 = filter.selectTransformer(previous, rawG, forward);
if (next != previous) {
// there is a root 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 root, 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();
// 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);
}
}
}
/** Local handler. */
private static class LocalHandler<T extends EventDetector> implements EventHandler<EventSlopeFilter<T>> {
/** {@inheritDoc} */
public Action eventOccurred(final SpacecraftState s, final EventSlopeFilter<T> ef, final boolean increasing) {
return ef.rawDetector.eventOccurred(s, ef.filter.getTriggeredIncreasing());
}
/** {@inheritDoc} */
@Override
public SpacecraftState resetState(final EventSlopeFilter<T> ef, final SpacecraftState oldState) {
return ef.rawDetector.resetState(oldState);
}
}
}