AbstractTimeInterpolator.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.time;

  19. import org.hipparchus.util.FastMath;
  20. import org.orekit.errors.OrekitIllegalArgumentException;
  21. import org.orekit.errors.OrekitInternalError;
  22. import org.orekit.errors.OrekitMessages;
  23. import org.orekit.utils.ImmutableTimeStampedCache;

  25. import java.util.ArrayList;
  26. import java.util.Collection;
  27. import java.util.Collections;
  28. import java.util.List;
  29. import java.util.Optional;
  30. import java.util.stream.Collectors;
  31. import java.util.stream.Stream;

  33. /**
  34.  * Abstract class for time interpolator.
  35.  *
  36.  * @param <T> interpolated time stamped type
  37.  *
  38.  * @author Vincent Cucchietti
  39.  */
  40. public abstract class AbstractTimeInterpolator<T extends TimeStamped> implements TimeInterpolator<T> {

  42.     /** Default extrapolation time threshold: 1ms. */
  43.     public static final double DEFAULT_EXTRAPOLATION_THRESHOLD_SEC = 1e-3;

  45.     /** Default number of interpolation points. */
  46.     public static final int DEFAULT_INTERPOLATION_POINTS = 2;

  48.     /** The extrapolation threshold beyond which the propagation will fail. */
  49.     private final double extrapolationThreshold;

  51.     /** Neighbor size. */
  52.     private final int interpolationPoints;

  54.     /**
  55.      * Constructor.
  56.      *
  57.      * @param interpolationPoints number of interpolation points
  58.      * @param extrapolationThreshold extrapolation threshold beyond which the propagation will fail
  59.      */
  60.     public AbstractTimeInterpolator(final int interpolationPoints, final double extrapolationThreshold) {
  61.         this.interpolationPoints    = interpolationPoints;
  62.         this.extrapolationThreshold = extrapolationThreshold;
  63.     }

  65.     /**
  66.      * Method checking if given interpolator is compatible with given sample size.
  67.      *
  68.      * @param interpolator interpolator
  69.      * @param sampleSize sample size
  70.      */
  71.     public static void checkInterpolatorCompatibilityWithSampleSize(
  72.             final TimeInterpolator<? extends TimeStamped> interpolator,
  73.             final int sampleSize) {

  75.         // Retrieve all sub-interpolators (or a singleton list with given interpolator if there are no sub-interpolators)
  76.         final List<TimeInterpolator<? extends TimeStamped>> subInterpolators = interpolator.getSubInterpolators();
  77.         for (final TimeInterpolator<? extends TimeStamped> subInterpolator : subInterpolators) {
  78.             if (sampleSize < subInterpolator.getNbInterpolationPoints()) {
  79.                 throw new OrekitIllegalArgumentException(OrekitMessages.NOT_ENOUGH_DATA, sampleSize);
  80.             }
  81.         }
  82.     }

  84.     /** {@inheritDoc} */
  85.     @Override
  86.     public T interpolate(final AbsoluteDate interpolationDate, final Stream<T> sample) {
  87.         return interpolate(interpolationDate, sample.collect(Collectors.toList()));
  88.     }

  90.     /** {@inheritDoc}. */
  91.     @Override
  92.     public T interpolate(final AbsoluteDate interpolationDate, final Collection<T> sample) {
  93.         final InterpolationData interpolationData = new InterpolationData(interpolationDate, sample);
  94.         return interpolate(interpolationData);
  95.     }

  97.     /**
  98.      * Get the central date to use to find neighbors while taking into account extrapolation threshold.
  99.      *
  100.      * @param date interpolation date
  101.      * @param cachedSamples cached samples
  102.      * @param threshold extrapolation threshold
  103.      * @param <T> type of element
  104.      *
  105.      * @return central date to use to find neighbors
  106.      * @since 12.0.1
  107.      */
  108.     public static <T extends TimeStamped> AbsoluteDate getCentralDate(final AbsoluteDate date,
  109.                                                                       final ImmutableTimeStampedCache<T> cachedSamples,
  110.                                                                       final double threshold) {
  111.         final AbsoluteDate minDate = cachedSamples.getEarliest().getDate();
  112.         final AbsoluteDate maxDate = cachedSamples.getLatest().getDate();
  113.         return getCentralDate(date, minDate, maxDate, threshold);
  114.     }

  116.     /**
  117.      * Get the central date to use to find neighbors while taking into account extrapolation threshold.
  118.      *
  119.      * @param date interpolation date
  120.      * @param minDate earliest date in the sample.
  121.      * @param maxDate latest date in the sample.
  122.      * @param threshold extrapolation threshold
  123.      *
  124.      * @return central date to use to find neighbors
  125.      * @since 12.0.1
  126.      */
  127.     public static AbsoluteDate getCentralDate(final AbsoluteDate date,
  128.                                               final AbsoluteDate minDate,
  129.                                               final AbsoluteDate maxDate,
  130.                                               final double threshold) {
  131.         final AbsoluteDate central;

  133.         if (date.compareTo(minDate) < 0 && FastMath.abs(date.durationFrom(minDate)) <= threshold) {
  134.             // avoid TimeStampedCacheException as we are still within the tolerance before minDate
  135.             central = minDate;
  136.         } else if (date.compareTo(maxDate) > 0 && FastMath.abs(date.durationFrom(maxDate)) <= threshold) {
  137.             // avoid TimeStampedCacheException as we are still within the tolerance after maxDate
  138.             central = maxDate;
  139.         } else {
  140.             central = date;
  141.         }

  143.         return central;
  144.     }

  146.     /** {@inheritDoc} */
  147.     public List<TimeInterpolator<? extends TimeStamped>> getSubInterpolators() {
  148.         return Collections.singletonList(this);
  149.     }

  151.     /** {@inheritDoc} */
  152.     public int getNbInterpolationPoints() {
  153.         final List<TimeInterpolator<? extends TimeStamped>> subInterpolators = getSubInterpolators();
  154.         // In case the interpolator does not have sub interpolators
  155.         if (subInterpolators.size() == 1) {
  156.             return interpolationPoints;
  157.         }
  158.         // Otherwise find maximum number of interpolation points among sub interpolators
  159.         else {
  160.             final Optional<Integer> optionalMaxNbInterpolationPoints =
  161.                     subInterpolators.stream().map(TimeInterpolator::getNbInterpolationPoints).max(Integer::compareTo);
  162.             if (optionalMaxNbInterpolationPoints.isPresent()) {
  163.                 return optionalMaxNbInterpolationPoints.get();
  164.             } else {
  165.                 // This should never happen
  166.                 throw new OrekitInternalError(null);
  167.             }
  168.         }
  169.     }

  171.     /** {@inheritDoc} */
  172.     public double getExtrapolationThreshold() {
  173.         return extrapolationThreshold;
  174.     }

  176.     /**
  177.      * Add all lowest level sub interpolators to the sub interpolator list.
  178.      *
  179.      * @param subInterpolator optional sub interpolator to add
  180.      * @param subInterpolators list of sub interpolators
  181.      */
  182.     protected void addOptionalSubInterpolatorIfDefined(final TimeInterpolator<? extends TimeStamped> subInterpolator,
  183.                                                        final List<TimeInterpolator<? extends TimeStamped>> subInterpolators) {
  184.         // Add all lowest level sub interpolators
  185.         if (subInterpolator != null) {
  186.             subInterpolators.addAll(subInterpolator.getSubInterpolators());
  187.         }
  188.     }

  190.     /**
  191.      * Interpolate instance from given interpolation data.
  192.      *
  193.      * @param interpolationData interpolation data
  194.      *
  195.      * @return interpolated instance from given interpolation data.
  196.      */
  197.     protected abstract T interpolate(InterpolationData interpolationData);

  199.     /**
  200.      * Get the time parameter which lies between [0:1] by normalizing the difference between interpolating time and previous
  201.      * date by the Δt between tabulated values.
  202.      *
  203.      * @param interpolatingTime time at which we want to interpolate a value (between previous and next tabulated dates)
  204.      * @param previousDate previous tabulated value date
  205.      * @param nextDate next tabulated value date
  206.      *
  207.      * @return time parameter which lies between [0:1]
  208.      */
  209.     protected double getTimeParameter(final AbsoluteDate interpolatingTime,
  210.                                       final AbsoluteDate previousDate,
  211.                                       final AbsoluteDate nextDate) {
  212.         return interpolatingTime.durationFrom(previousDate) / nextDate.getDate().durationFrom(previousDate);
  213.     }

  215.     /**
  216.      * Nested class used to store interpolation data.
  217.      * <p>
  218.      * It makes the interpolator thread safe.
  219.      */
  220.     public class InterpolationData {

  222.         /** Interpolation date. */
  223.         private final AbsoluteDate interpolationDate;

  225.         /** Neighbor list around interpolation date. */
  226.         private final List<T> neighborList;

  228.         /**
  229.          * Constructor.
  230.          *
  231.          * @param interpolationDate interpolation date
  232.          * @param sample time stamped sample
  233.          */
  234.         protected InterpolationData(final AbsoluteDate interpolationDate, final Collection<T> sample) {
  235.             // Handle specific case that is not handled by the immutable time stamped cache constructor
  236.             if (sample.isEmpty()) {
  237.                 throw new OrekitIllegalArgumentException(OrekitMessages.NOT_ENOUGH_DATA, 0);
  238.             }

  240.             // TODO performance: create neighborsList without copying sample.
  241.             if (sample.size() == interpolationPoints) {
  242.                 // shortcut for simple case
  243.                 // copy list to make neighborList immutable
  244.                 this.neighborList = Collections.unmodifiableList(new ArrayList<>(sample));
  245.             } else {
  246.                 // else, select sample.

  248.                 // Create immutable time stamped cache
  249.                 final ImmutableTimeStampedCache<T> cachedSamples =
  250.                         new ImmutableTimeStampedCache<>(interpolationPoints, sample);

  252.                 // Find neighbors
  253.                 final AbsoluteDate central = AbstractTimeInterpolator.getCentralDate(
  254.                         interpolationDate,
  255.                         cachedSamples,
  256.                         extrapolationThreshold);
  257.                 final Stream<T> neighborsStream = cachedSamples.getNeighbors(central);

  259.                 // Convert to unmodifiable list
  260.                 this.neighborList = Collections.unmodifiableList(neighborsStream.collect(Collectors.toList()));
  261.             }

  263.             // Store interpolation date
  264.             this.interpolationDate = interpolationDate;
  265.         }

  267.         /** Get interpolation date.
  268.          * @return interpolation date
  269.          */
  270.         public AbsoluteDate getInterpolationDate() {
  271.             return interpolationDate;
  272.         }

  274.         /** Get neighbor list.
  275.          * @return neighbor list
  276.          */
  277.         public List<T> getNeighborList() {
  278.             return neighborList;
  279.         }

  281.     }
  282. }
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