EventShifter.java
/* Copyright 2002-2021 CS GROUP
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* 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
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* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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package org.orekit.propagation.events;
import org.hipparchus.ode.events.Action;
import org.hipparchus.util.FastMath;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.time.AbsoluteDate;
/** Wrapper shifting events occurrences times.
* <p>This class wraps an {@link EventDetector event detector} to slightly
* shift the events occurrences times. A typical use case is for handling
* operational delays before or after some physical event really occurs.</p>
* <p>For example, the satellite attitude mode may be switched from sun pointed
* to spin-stabilized a few minutes before eclipse entry, and switched back
* to sun pointed a few minutes after eclipse exit. This behavior is handled
* by wrapping an {@link EclipseDetector eclipse detector} into an instance
* of this class with a positive times shift for increasing events (eclipse exit)
* and a negative times shift for decreasing events (eclipse entry).</p>
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @see EventDetector
* @param <T> class type for the generic version
* @author Luc Maisonobe
*/
public class EventShifter<T extends EventDetector> extends AbstractDetector<EventShifter<T>> {
/** Event detector for the raw unshifted event. */
private final T detector;
/** Indicator for using shifted or unshifted states at event occurrence. */
private final boolean useShiftedStates;
/** Offset to apply to find increasing events. */
private final double increasingOffset;
/** Offset to apply to find decreasing events. */
private final double decreasingOffset;
/** Build a new instance.
* <p>The {@link #getMaxCheckInterval() max check interval}, the
* {@link #getThreshold() convergence threshold} of the raw unshifted
* events will be used for the shifted event. When an event occurs,
* the {@link #eventOccurred(SpacecraftState, boolean) eventOccurred}
* method of the raw unshifted events will be called (with spacecraft
* state at either the shifted or the unshifted event date depending
* on the <code>useShiftedStates</code> parameter).</p>
* @param detector event detector for the raw unshifted event
* @param useShiftedStates if true, the state provided to {@link
* #eventOccurred(SpacecraftState, boolean) eventOccurred} method of
* the <code>detector</code> will remain shifted, otherwise it will
* be <i>unshifted</i> to correspond to the underlying raw event.
* @param increasingTimeShift increasing events time shift.
* @param decreasingTimeShift decreasing events time shift.
*/
public EventShifter(final T detector, final boolean useShiftedStates,
final double increasingTimeShift, final double decreasingTimeShift) {
this(detector.getMaxCheckInterval(), detector.getThreshold(),
detector.getMaxIterationCount(), new LocalHandler<T>(),
detector, useShiftedStates, increasingTimeShift, decreasingTimeShift);
}
/** 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 detector event detector for the raw unshifted event
* @param useShiftedStates if true, the state provided to {@link
* #eventOccurred(SpacecraftState, boolean) eventOccurred} method of
* the <code>detector</code> will remain shifted, otherwise it will
* be <i>unshifted</i> to correspond to the underlying raw event.
* @param increasingTimeShift increasing events time shift.
* @param decreasingTimeShift decreasing events time shift.
* @since 6.1
*/
private EventShifter(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<? super EventShifter<T>> handler,
final T detector, final boolean useShiftedStates,
final double increasingTimeShift, final double decreasingTimeShift) {
super(maxCheck, threshold, maxIter, handler);
this.detector = detector;
this.useShiftedStates = useShiftedStates;
this.increasingOffset = -increasingTimeShift;
this.decreasingOffset = -decreasingTimeShift;
}
/** {@inheritDoc} */
@Override
protected EventShifter<T> create(final double newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler<? super EventShifter<T>> newHandler) {
return new EventShifter<T>(newMaxCheck, newThreshold, newMaxIter, newHandler,
detector, useShiftedStates, -increasingOffset, -decreasingOffset);
}
/** Get the increasing events time shift.
* @return increasing events time shift
*/
public double getIncreasingTimeShift() {
return -increasingOffset;
}
/** Get the decreasing events time shift.
* @return decreasing events time shift
*/
public double getDecreasingTimeShift() {
return -decreasingOffset;
}
/** {@inheritDoc} */
public void init(final SpacecraftState s0,
final AbsoluteDate t) {
super.init(s0, t);
detector.init(s0, t);
}
/** {@inheritDoc} */
public double g(final SpacecraftState s) {
final double incShiftedG = detector.g(s.shiftedBy(increasingOffset));
final double decShiftedG = detector.g(s.shiftedBy(decreasingOffset));
return (increasingOffset >= decreasingOffset) ?
FastMath.max(incShiftedG, decShiftedG) : FastMath.min(incShiftedG, decShiftedG);
}
/** Local class for handling events. */
private static class LocalHandler<T extends EventDetector> implements EventHandler<EventShifter<T>> {
/** Shifted state at even occurrence. */
private SpacecraftState shiftedState;
/** {@inheritDoc} */
public Action eventOccurred(final SpacecraftState s, final EventShifter<T> shifter, final boolean increasing) {
if (shifter.useShiftedStates) {
// the state provided by the caller already includes the time shift
shiftedState = s;
} else {
// we need to "unshift" the state
final double offset = increasing ? shifter.increasingOffset : shifter.decreasingOffset;
shiftedState = s.shiftedBy(offset);
}
return shifter.detector.eventOccurred(shiftedState, increasing);
}
/** {@inheritDoc} */
@Override
public SpacecraftState resetState(final EventShifter<T> shifter, final SpacecraftState oldState) {
return shifter.detector.resetState(shiftedState);
}
}
}