EventSlopeFilter.java

  1. /*
  2.  * Licensed to the Apache Software Foundation (ASF) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * The ASF 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.  */

  18. package org.orekit.propagation.events;

  20. import java.util.Arrays;

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

  27. /** Wrapper used to detect only increasing or decreasing events.
  28.  *
  29.  * <p>This class is heavily based on the class EventFilter from the
  30.  * Hipparchus library. The changes performed consist in replacing
  31.  * raw types (double and double arrays) with space dynamics types
  32.  * ({@link AbsoluteDate}, {@link SpacecraftState}).</p>
  33.  *
  34.  * <p>General {@link EventDetector events} are defined implicitly
  35.  * by a {@link EventDetector#g(SpacecraftState) g function} crossing
  36.  * zero. This function needs to be continuous in the event neighborhood,
  37.  * and its sign must remain consistent between events. This implies that
  38.  * during an orbit propagation, events triggered are alternately events
  39.  * for which the function increases from negative to positive values,
  40.  * and events for which the function decreases from positive to
  41.  * negative values.
  42.  * </p>
  43.  *
  44.  * <p>Sometimes, users are only interested in one type of event (say
  45.  * increasing events for example) and not in the other type. In these
  46.  * cases, looking precisely for all events location and triggering
  47.  * events that will later be ignored is a waste of computing time.</p>
  48.  *
  49.  * <p>Users can wrap a regular {@link EventDetector event detector} in
  50.  * an instance of this class and provide this wrapping instance to
  51.  * a {@link org.orekit.propagation.Propagator}
  52.  * in order to avoid wasting time looking for uninteresting events.
  53.  * The wrapper will intercept the calls to the {@link
  54.  * EventDetector#g(SpacecraftState) g function} and to the {@link
  55.  * EventHandler#eventOccurred(SpacecraftState, EventDetector, boolean)
  56.  * eventOccurred} method in order to ignore uninteresting events. The
  57.  * wrapped regular {@link EventDetector event detector} will then see only
  58.  * the interesting events, i.e. either only {@code increasing} events or
  59.  * only {@code decreasing} events. The number of calls to the {@link
  60.  * EventDetector#g(SpacecraftState) g function} will also be reduced.</p>
  61.  * @see EventEnablingPredicateFilter
  62.  * @param <T> type of the detector
  63.  */

  65. public class EventSlopeFilter<T extends EventDetector> extends AbstractDetector<EventSlopeFilter<T>> {

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

  70.     /** Wrapped event detector. */
  71.     private final T rawDetector;

  73.     /** Filter to use. */
  74.     private final FilterType filter;

  76.     /** Transformers of the g function. */
  77.     private final Transformer[] transformers;

  79.     /** Update time of the transformers. */
  80.     private final AbsoluteDate[] updates;

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

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

  88.     /** Wrap an {@link EventDetector event detector}.
  89.      * @param rawDetector event detector to wrap
  90.      * @param filter filter to use
  91.      */
  92.     public EventSlopeFilter(final T rawDetector, final FilterType filter) {
  93.         this(rawDetector.getMaxCheckInterval(), rawDetector.getThreshold(),
  94.              rawDetector.getMaxIterationCount(), new LocalHandler<>(),
  95.              rawDetector, filter);
  96.     }

  98.     /** Protected constructor with full parameters.
  99.      * <p>
  100.      * This constructor is not public as users are expected to use the builder
  101.      * API with the various {@code withXxx()} methods to set up the instance
  102.      * in a readable manner without using a huge amount of parameters.
  103.      * </p>
  104.      * @param maxCheck maximum checking interval
  105.      * @param threshold convergence threshold (s)
  106.      * @param maxIter maximum number of iterations in the event time search
  107.      * @param handler event handler to call at event occurrences
  108.      * @param rawDetector event detector to wrap
  109.      * @param filter filter to use
  110.      * @since 6.1
  111.      */
  112.     protected EventSlopeFilter(final AdaptableInterval maxCheck, final double threshold,
  113.                                final int maxIter, final EventHandler handler,
  114.                                final T rawDetector, final FilterType filter) {
  115.         super(new EventDetectionSettings(maxCheck, threshold, maxIter), handler);
  116.         this.rawDetector  = rawDetector;
  117.         this.filter       = filter;
  118.         this.transformers = new Transformer[HISTORY_SIZE];
  119.         this.updates      = new AbsoluteDate[HISTORY_SIZE];
  120.     }

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

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

  138.     /** Get filter type.
  139.      * @return filter type
  140.      */
  141.     public FilterType getFilter() {
  142.         return filter;
  143.     }

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

  150.         // delegate to raw detector
  151.         rawDetector.init(s0, t);

  153.         // initialize events triggering logic
  154.         forward  = t.compareTo(s0.getDate()) >= 0;
  155.         extremeT = forward ? AbsoluteDate.PAST_INFINITY : AbsoluteDate.FUTURE_INFINITY;
  156.         Arrays.fill(transformers, Transformer.UNINITIALIZED);
  157.         Arrays.fill(updates, extremeT);

  159.     }

  161.     /**  {@inheritDoc} */
  162.     public double g(final SpacecraftState s) {

  164.         final double rawG = rawDetector.g(s);

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

  172.                 // check if a new rough root has been crossed
  173.                 final Transformer previous = transformers[last];
  174.                 final Transformer next     = filter.selectTransformer(previous, rawG, forward);
  175.                 if (next != previous) {
  176.                     // there is a root somewhere between extremeT and t.
  177.                     // the new transformer is valid for t (this is how we have just computed
  178.                     // it above), but it is in fact valid on both sides of the root, so
  179.                     // it was already valid before t and even up to previous time. We store
  180.                     // the switch at extremeT for safety, to ensure the previous transformer
  181.                     // is not applied too close of the root
  182.                     System.arraycopy(updates,      1, updates,      0, last);
  183.                     System.arraycopy(transformers, 1, transformers, 0, last);
  184.                     updates[last]      = extremeT;
  185.                     transformers[last] = next;
  186.                 }

  188.                 extremeT = s.getDate();

  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     = filter.selectTransformer(previous, rawG, forward);
  214.                 if (next != previous) {
  215.                     // there is a root 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 root, 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();

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

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

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

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

  245.             }
  246.         }

  248.     }

  250.     /** Local handler. */
  251.     private static class LocalHandler<T extends EventDetector> implements EventHandler {

  253.         /** {@inheritDoc} */
  254.         public Action eventOccurred(final SpacecraftState s, final EventDetector detector, final boolean increasing) {
  255.             @SuppressWarnings("unchecked")
  256.             final EventSlopeFilter<T> esf = (EventSlopeFilter<T>) detector;
  257.             return esf.rawDetector.getHandler().eventOccurred(s, esf.rawDetector, esf.filter.getTriggeredIncreasing());
  258.         }

  260.         /** {@inheritDoc} */
  261.         @Override
  262.         public SpacecraftState resetState(final EventDetector detector, final SpacecraftState oldState) {
  263.             @SuppressWarnings("unchecked")
  264.             final EventSlopeFilter<T> esf = (EventSlopeFilter<T>) detector;
  265.             return esf.rawDetector.getHandler().resetState(esf.rawDetector, oldState);
  266.         }

  268.     }

  270. }
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