EventEnablingPredicateFilter.java

  1. /* Copyright 2002-2025 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 implements DetectorModifier {

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

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

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

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

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

  76.     /** Event detection settings. */
  77.     private final EventDetectionSettings detectionSettings;

  79.     /** Specialized event handler. */
  80.     private final LocalHandler handler;

  82.     /** Indicator for forward integration. */
  83.     private boolean forward;

  85.     /** Extreme time encountered so far. */
  86.     private AbsoluteDate extremeT;

  88.     /** Detector function value at extremeT. */
  89.     private double extremeG;

  91.     /** Wrap an {@link EventDetector event detector}.
  92.      * @param rawDetector event detector to wrap (its detection settings are taken as well)
  93.      * @param enabler event enabling predicate function to use
  94.      */
  95.     public EventEnablingPredicateFilter(final EventDetector rawDetector,
  96.                                         final EnablingPredicate enabler) {
  97.         this(rawDetector.getDetectionSettings(), rawDetector, enabler);
  98.     }

  100.     /** Constructor with full parameters.
  101.      * @param detectionSettings event detection settings
  102.      * @param rawDetector event detector to wrap
  103.      * @param enabler event enabling function to use
  104.      * @since 13.0
  105.      */
  106.     public EventEnablingPredicateFilter(final EventDetectionSettings detectionSettings,
  107.                                         final EventDetector rawDetector, final EnablingPredicate enabler) {
  108.         this.detectionSettings = detectionSettings;
  109.         this.handler = new LocalHandler();
  110.         this.rawDetector  = rawDetector;
  111.         this.enabler      = enabler;
  112.         this.transformers = new Transformer[HISTORY_SIZE];
  113.         this.updates      = new AbsoluteDate[HISTORY_SIZE];
  114.     }

  116.     /**
  117.      * Builds a new instance from the input detection settings.
  118.      * @param settings event detection settings to be used
  119.      * @return a new detector
  120.      */
  121.     public EventEnablingPredicateFilter withDetectionSettings(final EventDetectionSettings settings) {
  122.         return new EventEnablingPredicateFilter(settings, rawDetector, enabler);
  123.     }

  125.     /**
  126.      * Get the wrapped raw detector.
  127.      * @return the wrapped raw detector
  128.      * @since 11.1
  129.      */
  130.     public EventDetector getDetector() {
  131.         return rawDetector;
  132.     }

  134.     /** {@inheritDoc} */
  135.     @Override
  136.     public EventHandler getHandler() {
  137.         return handler;
  138.     }

  140.     /** {@inheritDoc} */
  141.     @Override
  142.     public EventDetectionSettings getDetectionSettings() {
  143.         return detectionSettings;
  144.     }

  146.     /**  {@inheritDoc} */
  147.     @Override
  148.     public void init(final SpacecraftState s0, final AbsoluteDate t) {
  149.         DetectorModifier.super.init(s0, t);

  151.         // initialize events triggering logic
  152.         forward  = AbstractDetector.checkIfForward(s0, t);
  153.         extremeT = forward ? AbsoluteDate.PAST_INFINITY : AbsoluteDate.FUTURE_INFINITY;
  154.         extremeG = Double.NaN;

  156.         Arrays.fill(transformers, Transformer.UNINITIALIZED);
  157.         Arrays.fill(updates, extremeT);

  159.     }

  161.     /**  {@inheritDoc} */
  162.     @Override
  163.     public void reset(final SpacecraftState state, final AbsoluteDate target) {
  164.         DetectorModifier.super.reset(state, target);
  165.         forward  = AbstractDetector.checkIfForward(state, target);
  166.         extremeT = forward ? AbsoluteDate.PAST_INFINITY : AbsoluteDate.FUTURE_INFINITY;
  167.         extremeG = Double.NaN;
  168.     }

  170.     /**  {@inheritDoc} */
  171.     @Override
  172.     public double g(final SpacecraftState s) {

  174.         final double  rawG      = rawDetector.g(s);
  175.         final boolean isEnabled = enabler.eventIsEnabled(s, rawDetector, rawG);
  176.         if (Double.isNaN(extremeG)) {
  177.             extremeG = rawG;
  178.         }

  180.         // search which transformer should be applied to g
  181.         if (isForward()) {
  182.             final int last = transformers.length - 1;
  183.             if (extremeT.compareTo(s.getDate()) < 0) {
  184.                 // we are at the forward end of the history

  186.                 // check if enabled status has changed
  187.                 final Transformer previous = transformers[last];
  188.                 final Transformer next     = selectTransformer(previous, extremeG, isEnabled);
  189.                 if (next != previous) {
  190.                     // there is a status change somewhere between extremeT and t.
  191.                     // the new transformer is valid for t (this is how we have just computed
  192.                     // it above), but it is in fact valid on both sides of the change, so
  193.                     // it was already valid before t and even up to previous time. We store
  194.                     // the switch at extremeT for safety, to ensure the previous transformer
  195.                     // is not applied too close of the root
  196.                     System.arraycopy(updates,      1, updates,      0, last);
  197.                     System.arraycopy(transformers, 1, transformers, 0, last);
  198.                     updates[last]      = extremeT;
  199.                     transformers[last] = next;
  200.                 }

  202.                 extremeT = s.getDate();
  203.                 extremeG = rawG;

  205.                 // apply the transform
  206.                 return next.transformed(rawG);

  208.             } else {
  209.                 // we are in the middle of the history

  211.                 // select the transformer
  212.                 for (int i = last; i > 0; --i) {
  213.                     if (updates[i].compareTo(s.getDate()) <= 0) {
  214.                         // apply the transform
  215.                         return transformers[i].transformed(rawG);
  216.                     }
  217.                 }

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

  221.             }
  222.         } else {
  223.             if (s.getDate().compareTo(extremeT) < 0) {
  224.                 // we are at the backward end of the history

  226.                 // check if a new rough root has been crossed
  227.                 final Transformer previous = transformers[0];
  228.                 final Transformer next     = selectTransformer(previous, extremeG, isEnabled);
  229.                 if (next != previous) {
  230.                     // there is a status change somewhere between extremeT and t.
  231.                     // the new transformer is valid for t (this is how we have just computed
  232.                     // it above), but it is in fact valid on both sides of the change, so
  233.                     // it was already valid before t and even up to previous time. We store
  234.                     // the switch at extremeT for safety, to ensure the previous transformer
  235.                     // is not applied too close of the root
  236.                     System.arraycopy(updates,      0, updates,      1, updates.length - 1);
  237.                     System.arraycopy(transformers, 0, transformers, 1, transformers.length - 1);
  238.                     updates[0]      = extremeT;
  239.                     transformers[0] = next;
  240.                 }

  242.                 extremeT = s.getDate();
  243.                 extremeG = rawG;

  245.                 // apply the transform
  246.                 return next.transformed(rawG);

  248.             } else {
  249.                 // we are in the middle of the history

  251.                 // select the transformer
  252.                 for (int i = 0; i < updates.length - 1; ++i) {
  253.                     if (s.getDate().compareTo(updates[i]) <= 0) {
  254.                         // apply the transform
  255.                         return transformers[i].transformed(rawG);
  256.                     }
  257.                 }

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

  261.             }
  262.         }

  264.     }

  266.     /** Get next function transformer in the specified direction.
  267.      * @param previous transformer active on the previous point with respect
  268.      * to integration direction (may be null if no previous point is known)
  269.      * @param previousG value of the g function at the previous point
  270.      * @param isEnabled if true the event should be enabled now
  271.      * @return next transformer transformer
  272.      */
  273.     private Transformer selectTransformer(final Transformer previous, final double previousG, final boolean isEnabled) {
  274.         if (isEnabled) {
  275.             // we need to select a transformer that can produce zero crossings,
  276.             // so it is either Transformer.PLUS or Transformer.MINUS
  277.             switch (previous) {
  278.                 case UNINITIALIZED :
  279.                     return Transformer.PLUS; // this initial choice is arbitrary, it could have been Transformer.MINUS
  280.                 case MIN :
  281.                     return previousG >= 0 ? Transformer.MINUS : Transformer.PLUS;
  282.                 case MAX :
  283.                     return previousG >= 0 ? Transformer.PLUS : Transformer.MINUS;
  284.                 default :
  285.                     return previous;
  286.             }
  287.         } else {
  288.             // we need to select a transformer that cannot produce any zero crossings,
  289.             // so it is either Transformer.MAX or Transformer.MIN
  290.             switch (previous) {
  291.                 case UNINITIALIZED :
  292.                     return Transformer.MAX; // this initial choice is arbitrary, it could have been Transformer.MIN
  293.                 case PLUS :
  294.                     return previousG >= 0 ? Transformer.MAX : Transformer.MIN;
  295.                 case MINUS :
  296.                     return previousG >= 0 ? Transformer.MIN : Transformer.MAX;
  297.                 default :
  298.                     return previous;
  299.             }
  300.         }
  301.     }

  303.     /** Check if the current propagation is forward or backward.
  304.      * @return true if the current propagation is forward
  305.      */
  306.     public boolean isForward() {
  307.         return forward;
  308.     }

  310.     /** Local handler. */
  311.     private static class LocalHandler implements EventHandler {

  313.         /** {@inheritDoc} */
  314.         public Action eventOccurred(final SpacecraftState s, final EventDetector detector, final boolean increasing) {
  315.             final EventEnablingPredicateFilter ef = (EventEnablingPredicateFilter) detector;
  316.             final Transformer transformer = ef.isForward() ? ef.transformers[ef.transformers.length - 1] : ef.transformers[0];
  317.             return ef.rawDetector.getHandler().eventOccurred(s, ef.rawDetector, transformer == Transformer.PLUS ? increasing : !increasing);
  318.         }

  320.         /** {@inheritDoc} */
  321.         @Override
  322.         public SpacecraftState resetState(final EventDetector detector, final SpacecraftState oldState) {
  323.             final EventEnablingPredicateFilter ef = (EventEnablingPredicateFilter) detector;
  324.             return ef.rawDetector.getHandler().resetState(ef.rawDetector, oldState);
  325.         }

  327.     }

  329. }
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