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* Licensed to CS Systèmes d'Information (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
* 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.
*/
package org.orekit.propagation.events;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.NoSuchElementException;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitException;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.ContinueOnEvent;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.time.AbsoluteDate;
/**
* 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 BooleanDetector 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 EclipseDetector}, {@link ElevationDetector}, {@link
* LatitudeCrossingDetector}. Using this detector with detectors that are not based on
* entry to or exit from a region, e.g. {@link DateDetector}, {@link
* LongitudeCrossingDetector}, will likely lead to unexpected results. To apply conditions
* to this latter type of event detectors a {@link EventEnablingPredicateFilter} is
* usually more appropriate.
*
* @author Evan Ward
* @see #and(Collection)
* @see #or(Collection)
* @see #not(EventDetector)
* @see EventEnablingPredicateFilter
* @see EventSlopeFilter
*/
public class BooleanDetector extends AbstractDetector<BooleanDetector> {
/** Serializable UID. */
private static final long serialVersionUID = 20170410L;
/** Original detectors: the operands. */
private final List<EventDetector> 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 newMaxCheck max check interval in seconds.
* @param newThreshold convergence threshold in seconds.
* @param newMaxIter max iterations.
* @param newHandler event handler.
*/
private BooleanDetector(final List<EventDetector> detectors,
final Operator operator,
final double newMaxCheck,
final double newThreshold,
final int newMaxIter,
final EventHandler<? super BooleanDetector> newHandler) {
super(newMaxCheck, newThreshold, newMaxIter, 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
* ContinueOnEvent}.
*
* @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 BooleanDetector
* @see #and(Collection)
* @see #or(EventDetector...)
* @see #not(EventDetector)
*/
public static BooleanDetector and(final EventDetector... detectors) {
return and(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
* ContinueOnEvent}.
*
* @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 BooleanDetector
* @see #and(EventDetector...)
* @see #or(Collection)
* @see #not(EventDetector)
*/
public static BooleanDetector and(
final Collection<? extends EventDetector> detectors) {
return new BooleanDetector(new ArrayList<>(detectors), // copy for immutability
Operator.AND,
detectors.stream().map(EventDetector::getMaxCheckInterval).min(Double::compareTo).get(),
detectors.stream().map(EventDetector::getThreshold).min(Double::compareTo).get(),
detectors.stream().map(EventDetector::getMaxIterationCount).min(Integer::compareTo).get(),
new ContinueOnEvent<>());
}
/**
* Create a new event detector that is the logical OR or 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
* ContinueOnEvent}.
*
* @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 BooleanDetector
* @see #or(Collection)
* @see #and(EventDetector...)
* @see #not(EventDetector)
*/
public static BooleanDetector or(final EventDetector... detectors) {
return or(Arrays.asList(detectors));
}
/**
* Create a new event detector that is the logical OR or 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
* ContinueOnEvent}.
*
* @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 BooleanDetector
* @see #or(EventDetector...)
* @see #and(Collection)
* @see #not(EventDetector)
*/
public static BooleanDetector or(
final Collection<? extends EventDetector> detectors) {
return new BooleanDetector(new ArrayList<>(detectors), // copy for immutability
Operator.OR,
detectors.stream().map(EventDetector::getMaxCheckInterval).min(Double::compareTo).get(),
detectors.stream().map(EventDetector::getThreshold).min(Double::compareTo).get(),
detectors.stream().map(EventDetector::getMaxIterationCount).min(Integer::compareTo).get(),
new ContinueOnEvent<>());
}
/**
* Create a new event detector that negates the g function of another detector.
*
* <p> This detector will be initialized with the same {@link
* EventDetector#getMaxCheckInterval()}, {@link EventDetector#getThreshold()}, and
* {@link EventDetector#getMaxIterationCount()} as {@code detector}. The event handler
* of the underlying detector is not used, instead the default handler is {@link
* ContinueOnEvent}.
*
* @param detector to negate.
* @return an new event detector whose g function is the same magnitude but opposite
* sign of {@code detector}.
* @see #and(Collection)
* @see #or(Collection)
* @see BooleanDetector
*/
public static NegateDetector not(final EventDetector detector) {
return new NegateDetector(detector);
}
@Override
public double g(final SpacecraftState s) throws OrekitException {
// can't use stream/lambda here because g(s) throws a checked exception
// so write out and combine the map and reduce loops
double ret = Double.NaN; // return value
boolean first = true;
for (final EventDetector 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 BooleanDetector create(final double newMaxCheck,
final double newThreshold,
final int newMaxIter,
final EventHandler<? super BooleanDetector> newHandler) {
return new BooleanDetector(detectors, operator, newMaxCheck, newThreshold,
newMaxIter, newHandler);
}
@Override
public void init(final SpacecraftState s0, final AbsoluteDate t) {
super.init(s0, t);
for (final EventDetector detector : detectors) {
detector.init(s0, t);
}
}
/** Local, serializable class for operator. */
private enum Operator {
/** And operator. */
AND() {
@Override
/** {@inheritDoc} */
public double combine(final double g1, final double g2) {
return FastMath.min(g1, g2);
}
},
/** Or operator. */
OR() {
@Override
/** {@inheritDoc} */
public double combine(final double g1, final double g2) {
return FastMath.max(g1, g2);
}
};
/** Combine two g functions evaluations.
* @param g1 first evaluation
* @param g2 second evaluation
* @return combined evaluation
*/
public abstract double combine(double g1, double g2);
};
}