FieldBooleanDetector.java
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* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* 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
*
* Unless required by applicable law or agreed to in writing, software
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package org.orekit.propagation.events;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.List;
import java.util.NoSuchElementException;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.util.FastMath;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.events.handlers.FieldContinueOnEvent;
import org.orekit.propagation.events.handlers.FieldEventHandler;
import org.orekit.time.FieldAbsoluteDate;
/**
* This class provides AND and OR operations for event detectors. This class treats
* positive values of the g function as true and negative values as false.
*
* <p> One example for an imaging satellite might be to only detect events when a
* satellite is overhead (elevation > 0) AND when the ground point is sunlit (Sun
* elevation > 0). Another slightly contrived example using the OR operator would be to
* detect access to a set of ground stations and only report events when the satellite
* enters or leaves the field of view of the set, but not hand-offs between the ground
* stations.
*
* <p> For the FieldBooleanDetector is important that the sign of the g function of the
* underlying event detector is not arbitrary, but has a semantic meaning, e.g. in or out,
* true or false. This class works well with event detectors that detect entry to or exit
* from a region, e.g. {@link FieldEclipseDetector}, {@link FieldElevationDetector}, {@link
* FieldLatitudeCrossingDetector}. Using this detector with detectors that are not based on
* entry to or exit from a region, e.g. {@link FieldDateDetector}, will likely lead to
* unexpected results. To apply conditions to this latter type of event detectors a
* {@link FieldEventEnablingPredicateFilter} is usually more appropriate.
*
* @param <T> type of the field elements
* @since 12.0
* @author Evan Ward
* @author luc Luc Maisonobe
* @see #andCombine(Collection)
* @see #orCombine(Collection)
* @see #notCombine(FieldEventDetector)
* @see EventEnablingPredicateFilter
* @see EventSlopeFilter
*/
public class FieldBooleanDetector<T extends CalculusFieldElement<T>> extends FieldAbstractDetector<FieldBooleanDetector<T>, T> {
/** Original detectors: the operands. */
private final List<FieldEventDetector<T>> detectors;
/** The composition function. Should be associative for predictable behavior. */
private final Operator operator;
/**
* Private constructor with all the parameters.
*
* @param detectors the operands.
* @param operator reduction operator to apply to value of the g function of the
* operands.
* @param detectionSettings event detection settings.
* @param newHandler event handler.
* @since 13.0
*/
protected FieldBooleanDetector(final List<FieldEventDetector<T>> detectors,
final Operator operator,
final FieldEventDetectionSettings<T> detectionSettings,
final FieldEventHandler<T> newHandler) {
super(detectionSettings, newHandler);
this.detectors = detectors;
this.operator = operator;
}
/**
* Create a new event detector that is the logical AND of the given event detectors.
*
* <p> The created event detector's g function is positive if and only if the g
* functions of all detectors in {@code detectors} are positive.
*
* <p> The starting interval, threshold, and iteration count are set to the most
* stringent (minimum) of all the {@code detectors}. The event handlers of the
* underlying {@code detectors} are not used, instead the default handler is {@link
* FieldContinueOnEvent}.
*
* @param <T> type of the field elements
* @param detectors the operands. Must contain at least one detector.
* @return a new event detector that is the logical AND of the operands.
* @throws NoSuchElementException if {@code detectors} is empty.
* @see FieldBooleanDetector
* @see #andCombine(Collection)
* @see #orCombine(FieldEventDetector...)
* @see #notCombine(FieldEventDetector)
*/
@SafeVarargs
public static <T extends CalculusFieldElement<T>> FieldBooleanDetector<T> andCombine(final FieldEventDetector<T>... detectors) {
return andCombine(Arrays.asList(detectors));
}
/**
* Create a new event detector that is the logical AND of the given event detectors.
*
* <p> The created event detector's g function is positive if and only if the g
* functions of all detectors in {@code detectors} are positive.
*
* <p> The starting interval, threshold, and iteration count are set to the most
* stringent (minimum) of the {@code detectors}. The event handlers of the
* underlying {@code detectors} are not used, instead the default handler is {@link
* FieldContinueOnEvent}.
*
* @param <T> type of the field elements
* @param detectors the operands. Must contain at least one detector.
* @return a new event detector that is the logical AND of the operands.
* @throws NoSuchElementException if {@code detectors} is empty.
* @see FieldBooleanDetector
* @see #andCombine(FieldEventDetector...)
* @see #orCombine(Collection)
* @see #notCombine(FieldEventDetector)
*/
public static <T extends CalculusFieldElement<T>> FieldBooleanDetector<T> andCombine(final Collection<? extends FieldEventDetector<T>> detectors) {
return new FieldBooleanDetector<>(new ArrayList<>(detectors), // copy for immutability
Operator.AND,
new FieldEventDetectionSettings<>((s, isForward) -> {
double minInterval = Double.POSITIVE_INFINITY;
for (final FieldEventDetector<T> detector : detectors) {
minInterval = FastMath.min(minInterval, detector.getMaxCheckInterval().currentInterval(s, isForward));
}
return minInterval;
},
detectors.stream().map(FieldEventDetector::getThreshold).min(new FieldComparator<>()).get(),
detectors.stream().map(FieldEventDetector::getMaxIterationCount).min(Integer::compareTo).get()),
new FieldContinueOnEvent<>());
}
/**
* Create a new event detector that is the logical OR of the given event detectors.
*
* <p> The created event detector's g function is positive if and only if at least
* one of g functions of the event detectors in {@code detectors} is positive.
*
* <p> The starting interval, threshold, and iteration count are set to the most
* stringent (minimum) of the {@code detectors}. The event handlers of the
* underlying EventDetectors are not used, instead the default handler is {@link
* FieldContinueOnEvent}.
*
* @param <T> type of the field elements
* @param detectors the operands. Must contain at least one detector.
* @return a new event detector that is the logical OR of the operands.
* @throws NoSuchElementException if {@code detectors} is empty.
* @see FieldBooleanDetector
* @see #orCombine(Collection)
* @see #andCombine(FieldEventDetector...)
* @see #notCombine(FieldEventDetector)
*/
@SafeVarargs
public static <T extends CalculusFieldElement<T>> FieldBooleanDetector<T> orCombine(final FieldEventDetector<T>... detectors) {
return orCombine(Arrays.asList(detectors));
}
/**
* Create a new event detector that is the logical OR of the given event detectors.
*
* <p> The created event detector's g function is positive if and only if at least
* one of g functions of the event detectors in {@code detectors} is positive.
*
* <p> The starting interval, threshold, and iteration count are set to the most
* stringent (minimum) of the {@code detectors}. The event handlers of the
* underlying EventDetectors are not used, instead the default handler is {@link
* FieldContinueOnEvent}.
*
* @param <T> type of the field elements
* @param detectors the operands. Must contain at least one detector.
* @return a new event detector that is the logical OR of the operands.
* @throws NoSuchElementException if {@code detectors} is empty.
* @see FieldBooleanDetector
* @see #orCombine(FieldEventDetector...)
* @see #andCombine(Collection)
* @see #notCombine(FieldEventDetector)
*/
public static <T extends CalculusFieldElement<T>> FieldBooleanDetector<T> orCombine(final Collection<? extends FieldEventDetector<T>> detectors) {
return new FieldBooleanDetector<>(new ArrayList<>(detectors), // copy for immutability
Operator.OR,
new FieldEventDetectionSettings<>((s, isForward) -> {
double minInterval = Double.POSITIVE_INFINITY;
for (final FieldEventDetector<T> detector : detectors) {
minInterval = FastMath.min(minInterval, detector.getMaxCheckInterval().currentInterval(s, isForward));
}
return minInterval;
},
detectors.stream().map(FieldEventDetector::getThreshold).min(new FieldComparator<>()).get(),
detectors.stream().map(FieldEventDetector::getMaxIterationCount).min(Integer::compareTo).get()),
new FieldContinueOnEvent<>());
}
/**
* Create a new event detector that negates the g function of another detector.
*
* <p> This detector will be initialized with the same {@link
* FieldEventDetector#getMaxCheckInterval()}, {@link FieldEventDetector#getThreshold()}, and
* {@link FieldEventDetector#getMaxIterationCount()} as {@code detector}. The event handler
* of the underlying detector is not used, instead the default handler is {@link
* FieldContinueOnEvent}.
*
* @param <T> type of the field elements
* @param detector to negate.
* @return an new event detector whose g function is the same magnitude but opposite
* sign of {@code detector}.
* @see #andCombine(Collection)
* @see #orCombine(Collection)
* @see FieldBooleanDetector
*/
public static <T extends CalculusFieldElement<T>> FieldNegateDetector<T> notCombine(final FieldEventDetector<T> detector) {
return new FieldNegateDetector<>(detector);
}
@Override
public T g(final FieldSpacecraftState<T> s) {
// can't use stream/lambda here because g(s) throws a checked exception
// so write out and combine the map and reduce loops
T ret = s.getDate().getField().getZero().newInstance(Double.NaN); // return value
boolean first = true;
for (final FieldEventDetector<T> detector : detectors) {
if (first) {
ret = detector.g(s);
first = false;
} else {
ret = operator.combine(ret, detector.g(s));
}
}
// return the result of applying the operator to all operands
return ret;
}
@Override
protected FieldBooleanDetector<T> create(final FieldEventDetectionSettings<T> detectionSettings,
final FieldEventHandler<T> newHandler) {
return new FieldBooleanDetector<>(detectors, operator, detectionSettings, newHandler);
}
@Override
public void init(final FieldSpacecraftState<T> s0,
final FieldAbsoluteDate<T> t) {
super.init(s0, t);
for (final FieldEventDetector<T> detector : detectors) {
detector.init(s0, t);
}
}
/**
* Get the list of original detectors.
* @return the list of original detectors
*/
public List<FieldEventDetector<T>> getDetectors() {
return new ArrayList<>(detectors);
}
/** Local class for operator. */
private enum Operator {
/** And operator. */
AND() {
@Override
/** {@inheritDoc} */
public <T extends CalculusFieldElement<T>> T combine(final T g1, final T g2) {
return FastMath.min(g1, g2);
}
},
/** Or operator. */
OR() {
@Override
/** {@inheritDoc} */
public <T extends CalculusFieldElement<T>> T combine(final T g1, final T g2) {
return FastMath.max(g1, g2);
}
};
/** Combine two g functions evaluations.
* @param <T> type of the field elements
* @param g1 first evaluation
* @param g2 second evaluation
* @return combined evaluation
*/
public abstract <T extends CalculusFieldElement<T>> T combine(T g1, T g2);
}
/** Comparator for field elements.
* @param <T> type of the field elements
*/
private static class FieldComparator<T extends CalculusFieldElement<T>> implements Comparator<T>, Serializable {
public int compare(final T t1, final T t2) {
return Double.compare(t1.getReal(), t2.getReal());
}
}
}