EventEnablingPredicateFilter.java

  1. /* Copyright 2002-2024 CS GROUP
  2.  * Licensed to CS GROUP (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.propagation.events;

  19. import java.util.Arrays;

  21. import org.hipparchus.ode.events.Action;
  22. import org.orekit.propagation.SpacecraftState;
  23. import org.orekit.propagation.events.handlers.EventHandler;
  24. import org.orekit.time.AbsoluteDate;

  26. /** Wrapper used to detect events only when enabled by an external predicated function.
  27.  *
  28.  * <p>General {@link EventDetector events} are defined implicitly
  29.  * by a {@link EventDetector#g(SpacecraftState) g function} crossing
  30.  * zero. This implies that during an orbit propagation, events are
  31.  * triggered at all zero crossings.
  32.  * </p>
  33.  *
  34.  * <p>Sometimes, users would like to enable or disable events by themselves,
  35.  * for example to trigger them only for certain orbits, or to check elevation
  36.  * maximums only when elevation itself is positive (i.e. they want to
  37.  * discard elevation maximums below ground). In these cases, looking precisely
  38.  * for all events location and triggering events that will later be ignored
  39.  * is a waste of computing time.</p>
  40.  *
  41.  * <p>Users can wrap a regular {@link EventDetector event detector} in
  42.  * an instance of this class and provide this wrapping instance to
  43.  * a {@link org.orekit.propagation.Propagator}
  44.  * in order to avoid wasting time looking for uninteresting events.
  45.  * The wrapper will intercept the calls to the {@link
  46.  * EventDetector#g(SpacecraftState) g function} and to the {@link
  47.  * EventHandler#eventOccurred(SpacecraftState, EventDetector, boolean)
  48.  * eventOccurred} method in order to ignore uninteresting events. The
  49.  * wrapped regular {@link EventDetector event detector} will the see only
  50.  * the interesting events, i.e. either only events that occur when a
  51.  * user-provided event enabling predicate function is true, ignoring all events
  52.  * that occur when the event enabling predicate function is false. The number of
  53.  * calls to the {@link EventDetector#g(SpacecraftState) g function} will also be
  54.  * reduced.</p>
  55.  * @see EventSlopeFilter
  56.  * @since 7.1
  57.  */

  59. public class EventEnablingPredicateFilter
  60.     extends AbstractDetector<EventEnablingPredicateFilter> {

  62.     /** Number of past transformers updates stored. */
  63.     private static final int HISTORY_SIZE = 100;

  65.     /** Wrapped event detector. */
  66.     private final EventDetector rawDetector;

  68.     /** Enabling predicate function. */
  69.     private final EnablingPredicate enabler;

  71.     /** Transformers of the g function. */
  72.     private final Transformer[] transformers;

  74.     /** Update time of the transformers. */
  75.     private final AbsoluteDate[] updates;

  77.     /** Indicator for forward integration. */
  78.     private boolean forward;

  80.     /** Extreme time encountered so far. */
  81.     private AbsoluteDate extremeT;

  83.     /** Detector function value at extremeT. */
  84.     private double extremeG;

  86.     /** Wrap an {@link EventDetector event detector}.
  87.      * @param rawDetector event detector to wrap
  88.      * @param enabler event enabling predicate function to use
  89.      */
  90.     public EventEnablingPredicateFilter(final EventDetector rawDetector,
  91.                                         final EnablingPredicate enabler) {
  92.         this(rawDetector.getMaxCheckInterval(), rawDetector.getThreshold(),
  93.              rawDetector.getMaxIterationCount(), new LocalHandler(),
  94.              rawDetector, enabler);
  95.     }

  97.     /** Protected constructor with full parameters.
  98.      * <p>
  99.      * This constructor is not public as users are expected to use the builder
  100.      * API with the various {@code withXxx()} methods to set up the instance
  101.      * in a readable manner without using a huge amount of parameters.
  102.      * </p>
  103.      * @param maxCheck maximum checking interval
  104.      * @param threshold convergence threshold (s)
  105.      * @param maxIter maximum number of iterations in the event time search
  106.      * @param handler event handler to call at event occurrences
  107.      * @param rawDetector event detector to wrap
  108.      * @param enabler event enabling function to use
  109.      */
  110.     protected EventEnablingPredicateFilter(final AdaptableInterval maxCheck, final double threshold,
  111.                                            final int maxIter, final EventHandler handler,
  112.                                            final EventDetector rawDetector,
  113.                                            final EnablingPredicate enabler) {
  114.         super(new EventDetectionSettings(maxCheck, threshold, maxIter), handler);
  115.         this.rawDetector  = rawDetector;
  116.         this.enabler      = enabler;
  117.         this.transformers = new Transformer[HISTORY_SIZE];
  118.         this.updates      = new AbsoluteDate[HISTORY_SIZE];
  119.     }

  121.     /** {@inheritDoc} */
  122.     @Override
  123.     protected EventEnablingPredicateFilter create(final AdaptableInterval newMaxCheck, final double newThreshold,
  124.                                                   final int newMaxIter,
  125.                                                   final EventHandler newHandler) {
  126.         return new EventEnablingPredicateFilter(newMaxCheck, newThreshold, newMaxIter, newHandler, rawDetector, enabler);
  127.     }

  129.     /**
  130.      * Get the wrapped raw detector.
  131.      * @return the wrapped raw detector
  132.      * @since 11.1
  133.      */
  134.     public EventDetector getDetector() {
  135.         return rawDetector;
  136.     }

  138.     /**  {@inheritDoc} */
  139.     @Override
  140.     public void init(final SpacecraftState s0,
  141.                      final AbsoluteDate t) {
  142.         super.init(s0, t);

  144.         // delegate to raw detector
  145.         rawDetector.init(s0, t);

  147.         // initialize events triggering logic
  148.         forward  = t.compareTo(s0.getDate()) >= 0;
  149.         extremeT = forward ? AbsoluteDate.PAST_INFINITY : AbsoluteDate.FUTURE_INFINITY;
  150.         extremeG = Double.NaN;
  151.         Arrays.fill(transformers, Transformer.UNINITIALIZED);
  152.         Arrays.fill(updates, extremeT);

  154.     }

  156.     /**  {@inheritDoc} */
  157.     public double g(final SpacecraftState s) {

  159.         final double  rawG      = rawDetector.g(s);
  160.         final boolean isEnabled = enabler.eventIsEnabled(s, rawDetector, rawG);
  161.         if (Double.isNaN(extremeG)) {
  162.             extremeG = rawG;
  163.         }

  165.         // search which transformer should be applied to g
  166.         if (forward) {
  167.             final int last = transformers.length - 1;
  168.             if (extremeT.compareTo(s.getDate()) < 0) {
  169.                 // we are at the forward end of the history

  171.                 // check if enabled status has changed
  172.                 final Transformer previous = transformers[last];
  173.                 final Transformer next     = selectTransformer(previous, extremeG, isEnabled);
  174.                 if (next != previous) {
  175.                     // there is a status change somewhere between extremeT and t.
  176.                     // the new transformer is valid for t (this is how we have just computed
  177.                     // it above), but it is in fact valid on both sides of the change, so
  178.                     // it was already valid before t and even up to previous time. We store
  179.                     // the switch at extremeT for safety, to ensure the previous transformer
  180.                     // is not applied too close of the root
  181.                     System.arraycopy(updates,      1, updates,      0, last);
  182.                     System.arraycopy(transformers, 1, transformers, 0, last);
  183.                     updates[last]      = extremeT;
  184.                     transformers[last] = next;
  185.                 }

  187.                 extremeT = s.getDate();
  188.                 extremeG = rawG;

  190.                 // apply the transform
  191.                 return next.transformed(rawG);

  193.             } else {
  194.                 // we are in the middle of the history

  196.                 // select the transformer
  197.                 for (int i = last; i > 0; --i) {
  198.                     if (updates[i].compareTo(s.getDate()) <= 0) {
  199.                         // apply the transform
  200.                         return transformers[i].transformed(rawG);
  201.                     }
  202.                 }

  204.                 return transformers[0].transformed(rawG);

  206.             }
  207.         } else {
  208.             if (s.getDate().compareTo(extremeT) < 0) {
  209.                 // we are at the backward end of the history

  211.                 // check if a new rough root has been crossed
  212.                 final Transformer previous = transformers[0];
  213.                 final Transformer next     = selectTransformer(previous, extremeG, isEnabled);
  214.                 if (next != previous) {
  215.                     // there is a status change somewhere between extremeT and t.
  216.                     // the new transformer is valid for t (this is how we have just computed
  217.                     // it above), but it is in fact valid on both sides of the change, so
  218.                     // it was already valid before t and even up to previous time. We store
  219.                     // the switch at extremeT for safety, to ensure the previous transformer
  220.                     // is not applied too close of the root
  221.                     System.arraycopy(updates,      0, updates,      1, updates.length - 1);
  222.                     System.arraycopy(transformers, 0, transformers, 1, transformers.length - 1);
  223.                     updates[0]      = extremeT;
  224.                     transformers[0] = next;
  225.                 }

  227.                 extremeT = s.getDate();
  228.                 extremeG = rawG;

  230.                 // apply the transform
  231.                 return next.transformed(rawG);

  233.             } else {
  234.                 // we are in the middle of the history

  236.                 // select the transformer
  237.                 for (int i = 0; i < updates.length - 1; ++i) {
  238.                     if (s.getDate().compareTo(updates[i]) <= 0) {
  239.                         // apply the transform
  240.                         return transformers[i].transformed(rawG);
  241.                     }
  242.                 }

  244.                 return transformers[updates.length - 1].transformed(rawG);

  246.             }
  247.         }

  249.     }

  251.     /** Get next function transformer in the specified direction.
  252.      * @param previous transformer active on the previous point with respect
  253.      * to integration direction (may be null if no previous point is known)
  254.      * @param previousG value of the g function at the previous point
  255.      * @param isEnabled if true the event should be enabled now
  256.      * @return next transformer transformer
  257.      */
  258.     private Transformer selectTransformer(final Transformer previous, final double previousG, final boolean isEnabled) {
  259.         if (isEnabled) {
  260.             // we need to select a transformer that can produce zero crossings,
  261.             // so it is either Transformer.PLUS or Transformer.MINUS
  262.             switch (previous) {
  263.                 case UNINITIALIZED :
  264.                     return Transformer.PLUS; // this initial choice is arbitrary, it could have been Transformer.MINUS
  265.                 case MIN :
  266.                     return previousG >= 0 ? Transformer.MINUS : Transformer.PLUS;
  267.                 case MAX :
  268.                     return previousG >= 0 ? Transformer.PLUS : Transformer.MINUS;
  269.                 default :
  270.                     return previous;
  271.             }
  272.         } else {
  273.             // we need to select a transformer that cannot produce any zero crossings,
  274.             // so it is either Transformer.MAX or Transformer.MIN
  275.             switch (previous) {
  276.                 case UNINITIALIZED :
  277.                     return Transformer.MAX; // this initial choice is arbitrary, it could have been Transformer.MIN
  278.                 case PLUS :
  279.                     return previousG >= 0 ? Transformer.MAX : Transformer.MIN;
  280.                 case MINUS :
  281.                     return previousG >= 0 ? Transformer.MIN : Transformer.MAX;
  282.                 default :
  283.                     return previous;
  284.             }
  285.         }
  286.     }

  288.     /** Local handler. */
  289.     private static class LocalHandler implements EventHandler {

  291.         /** {@inheritDoc} */
  292.         public Action eventOccurred(final SpacecraftState s, final EventDetector detector, final boolean increasing) {
  293.             final EventEnablingPredicateFilter ef = (EventEnablingPredicateFilter) detector;
  294.             final Transformer transformer = ef.forward ? ef.transformers[ef.transformers.length - 1] : ef.transformers[0];
  295.             return ef.rawDetector.getHandler().eventOccurred(s, ef.rawDetector, transformer == Transformer.PLUS ? increasing : !increasing);
  296.         }

  298.         /** {@inheritDoc} */
  299.         @Override
  300.         public SpacecraftState resetState(final EventDetector detector, final SpacecraftState oldState) {
  301.             final EventEnablingPredicateFilter ef = (EventEnablingPredicateFilter) detector;
  302.             return ef.rawDetector.getHandler().resetState(ef.rawDetector, oldState);
  303.         }

  305.     }

  307. }
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