AbstractFieldTimeInterpolator.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.CalculusFieldElement;
  20. import org.hipparchus.Field;
  21. import org.hipparchus.util.FastMath;
  22. import org.orekit.errors.OrekitIllegalArgumentException;
  23. import org.orekit.errors.OrekitInternalError;
  24. import org.orekit.errors.OrekitMessages;
  25. import org.orekit.utils.ImmutableFieldTimeStampedCache;

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

  35. /**
  36.  * Abstract class for time interpolator.
  37.  *
  38.  * @param <T> interpolated time stamped type
  39.  * @param <KK> type of the field element
  40.  *
  41.  * @author Vincent Cucchietti
  42.  */
  43. public abstract class AbstractFieldTimeInterpolator<T extends FieldTimeStamped<KK>, KK extends CalculusFieldElement<KK>>
  44.         implements FieldTimeInterpolator<T, KK> {

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

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

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

  55.     /** Neighbor size. */
  56.     private final int interpolationPoints;

  58.     /**
  59.      * Constructor.
  60.      *
  61.      * @param interpolationPoints number of interpolation points
  62.      * @param extrapolationThreshold extrapolation threshold beyond which the propagation will fail
  63.      */
  64.     public AbstractFieldTimeInterpolator(final int interpolationPoints, final double extrapolationThreshold) {
  65.         this.interpolationPoints    = interpolationPoints;
  66.         this.extrapolationThreshold = extrapolationThreshold;
  67.     }

  69.     /**
  70.      * Method checking if given interpolator is compatible with given sample size.
  71.      *
  72.      * @param interpolator interpolator
  73.      * @param sampleSize sample size
  74.      * @param <T> type of the field elements
  75.      */
  76.     public static <T extends CalculusFieldElement<T>> void checkInterpolatorCompatibilityWithSampleSize(
  77.             final FieldTimeInterpolator<? extends FieldTimeStamped<T>, T> interpolator,
  78.             final int sampleSize) {

  80.         // Retrieve all sub-interpolators (or a singleton list with given interpolator if there are no sub-interpolators)
  81.         final List<FieldTimeInterpolator<? extends FieldTimeStamped<T>, T>> subInterpolators =
  82.                 interpolator.getSubInterpolators();
  83.         for (final FieldTimeInterpolator<? extends FieldTimeStamped<T>, T> subInterpolator : subInterpolators) {
  84.             if (sampleSize < subInterpolator.getNbInterpolationPoints()) {
  85.                 throw new OrekitIllegalArgumentException(OrekitMessages.NOT_ENOUGH_DATA, sampleSize);
  86.             }
  87.         }
  88.     }

  90.     /** {@inheritDoc} */
  91.     @Override
  92.     public T interpolate(final FieldAbsoluteDate<KK> interpolationDate, final Stream<T> sample) {
  93.         return interpolate(interpolationDate, sample.collect(Collectors.toList()));
  94.     }

  96.     /** {@inheritDoc}. */
  97.     @Override
  98.     public T interpolate(final FieldAbsoluteDate<KK> interpolationDate, final Collection<T> sample) {
  99.         final InterpolationData interpolationData = new InterpolationData(interpolationDate, sample);
  100.         return interpolate(interpolationData);
  101.     }

  103.     /**
  104.      * Get the central date to use to find neighbors while taking into account extrapolation threshold.
  105.      *
  106.      * @param date interpolation date
  107.      * @param cachedSamples cached samples
  108.      * @param threshold extrapolation threshold
  109.      * @param <T> type of time stamped element
  110.      * @param <KK> type of calculus field element
  111.      *
  112.      * @return central date to use to find neighbors
  113.      * @since 12.0.1
  114.      */
  115.     public static <T extends FieldTimeStamped<KK>, KK extends CalculusFieldElement<KK>> FieldAbsoluteDate<KK> getCentralDate(
  116.             final FieldAbsoluteDate<KK> date,
  117.             final ImmutableFieldTimeStampedCache<T, KK> cachedSamples,
  118.             final double threshold) {
  119.         return getCentralDate(
  120.                 date,
  121.                 cachedSamples.getEarliest().getDate(),
  122.                 cachedSamples.getLatest().getDate(),
  123.                 threshold);
  124.     }

  126.     /**
  127.      * Get the central date to use to find neighbors while taking into account extrapolation threshold.
  128.      *
  129.      * @param date interpolation date
  130.      * @param minDate earliest date in the sample.
  131.      * @param maxDate latest date in the sample.
  132.      * @param threshold extrapolation threshold
  133.      * @param <KK> type of calculus field element
  134.      *
  135.      * @return central date to use to find neighbors
  136.      * @since 12.0.1
  137.      */
  138.     public static <KK extends CalculusFieldElement<KK>> FieldAbsoluteDate<KK> getCentralDate(
  139.             final FieldAbsoluteDate<KK> date,
  140.             final FieldAbsoluteDate<KK> minDate,
  141.             final FieldAbsoluteDate<KK> maxDate,
  142.             final double threshold) {
  143.         final FieldAbsoluteDate<KK> central;

  145.         if (date.compareTo(minDate) < 0 && FastMath.abs(date.durationFrom(minDate)).getReal() <= threshold) {
  146.             // avoid TimeStampedCacheException as we are still within the tolerance before minDate
  147.             central = minDate;
  148.         } else if (date.compareTo(maxDate) > 0 && FastMath.abs(date.durationFrom(maxDate)).getReal() <= threshold) {
  149.             // avoid TimeStampedCacheException as we are still within the tolerance after maxDate
  150.             central = maxDate;
  151.         } else {
  152.             central = date;
  153.         }

  155.         return central;
  156.     }

  158.     /** {@inheritDoc} */
  159.     public List<FieldTimeInterpolator<? extends FieldTimeStamped<KK>, KK>> getSubInterpolators() {
  160.         return Collections.singletonList(this);
  161.     }

  163.     /** {@inheritDoc} */
  164.     public int getNbInterpolationPoints() {
  165.         final List<FieldTimeInterpolator<? extends FieldTimeStamped<KK>, KK>> subInterpolators = getSubInterpolators();
  166.         // In case the interpolator does not have sub interpolators
  167.         if (subInterpolators.size() == 1) {
  168.             return interpolationPoints;
  169.         }
  170.         // Otherwise find maximum number of interpolation points among sub interpolators
  171.         else {
  172.             final Optional<Integer> optionalMaxNbInterpolationPoints =
  173.                     subInterpolators.stream().map(FieldTimeInterpolator::getNbInterpolationPoints).max(Integer::compareTo);
  174.             if (optionalMaxNbInterpolationPoints.isPresent()) {
  175.                 return optionalMaxNbInterpolationPoints.get();
  176.             } else {
  177.                 // This should never happen
  178.                 throw new OrekitInternalError(null);
  179.             }
  180.         }
  181.     }

  183.     /** {@inheritDoc} */
  184.     public double getExtrapolationThreshold() {
  185.         return extrapolationThreshold;
  186.     }

  188.     /**
  189.      * Add all lowest level sub interpolators to the sub interpolator list.
  190.      *
  191.      * @param subInterpolator optional sub interpolator to add
  192.      * @param subInterpolators list of sub interpolators
  193.      * @param <S> type of the field element
  194.      */
  195.     protected <S extends CalculusFieldElement<S>> void addOptionalSubInterpolatorIfDefined(
  196.             final FieldTimeInterpolator<? extends FieldTimeStamped<S>, S> subInterpolator,
  197.             final List<FieldTimeInterpolator<? extends FieldTimeStamped<S>, S>> subInterpolators) {
  198.         // Add all lowest level sub interpolators
  199.         if (subInterpolator != null) {
  200.             subInterpolators.addAll(subInterpolator.getSubInterpolators());
  201.         }
  202.     }

  204.     /**
  205.      * Interpolate instance from given interpolation data.
  206.      *
  207.      * @param interpolationData interpolation data
  208.      *
  209.      * @return interpolated instance from given interpolation data.
  210.      */
  211.     protected abstract T interpolate(InterpolationData interpolationData);

  213.     /**
  214.      * Get the time parameter which lies between [0:1] by normalizing the difference between interpolating time and previous
  215.      * date by the Δt between tabulated values.
  216.      *
  217.      * @param interpolatingTime time at which we want to interpolate a value (between previous and next tabulated dates)
  218.      * @param previousDate previous tabulated value date
  219.      * @param nextDate next tabulated value date
  220.      *
  221.      * @return time parameter which lies between [0:1]
  222.      */
  223.     protected KK getTimeParameter(final FieldAbsoluteDate<KK> interpolatingTime,
  224.                                   final FieldAbsoluteDate<KK> previousDate,
  225.                                   final FieldAbsoluteDate<KK> nextDate) {

  227.         return interpolatingTime.durationFrom(previousDate).divide(nextDate.getDate().durationFrom(previousDate));
  228.     }

  230.     /**
  231.      * Nested class used to store interpolation data.
  232.      * <p>
  233.      * It makes the interpolator thread safe.
  234.      */
  235.     public class InterpolationData {

  237.         /** Interpolation date. */
  238.         private final FieldAbsoluteDate<KK> interpolationDate;

  240.         /** Unmodifiable list of neighbors. */
  241.         private final List<T> neighborList;

  243.         /** Field of the element. */
  244.         private final Field<KK> field;

  246.         /** Fielded zero. */
  247.         private final KK zero;

  249.         /** Fielded one. */
  250.         private final KK one;

  252.         /**
  253.          * Constructor.
  254.          *
  255.          * @param interpolationDate interpolation date
  256.          * @param sample time stamped sample
  257.          */
  258.         protected InterpolationData(final FieldAbsoluteDate<KK> interpolationDate, final Collection<T> sample) {
  259.             // Handle specific case that is not handled by the immutable time stamped cache constructor
  260.             if (sample.isEmpty()) {
  261.                 throw new OrekitIllegalArgumentException(OrekitMessages.NOT_ENOUGH_DATA, 0);
  262.             }

  264.             // TODO performance: create neighborsList without copying sample.
  265.             if (sample.size() == interpolationPoints) {
  266.                 // shortcut for simple case
  267.                 // copy list to make neighborList immutable
  268.                 this.neighborList = Collections.unmodifiableList(new ArrayList<>(sample));
  269.             } else {
  270.                 // else, select sample.

  272.                 // Create immutable time stamped cache
  273.                 final ImmutableFieldTimeStampedCache<T, KK> cachedSamples =
  274.                         new ImmutableFieldTimeStampedCache<>(interpolationPoints, sample);

  276.                 // Find neighbors
  277.                 final FieldAbsoluteDate<KK> central =
  278.                         AbstractFieldTimeInterpolator.getCentralDate(
  279.                                 interpolationDate,
  280.                                 cachedSamples,
  281.                                 extrapolationThreshold);
  282.                 final Stream<T> neighborsStream = cachedSamples.getNeighbors(central);

  284.                 // Convert to unmodifiable list
  285.                 neighborList = Collections.unmodifiableList(neighborsStream.collect(Collectors.toList()));
  286.             }

  288.             // Extract field and useful terms
  289.             this.field = interpolationDate.getField();
  290.             this.zero = field.getZero();
  291.             this.one = field.getOne();

  293.             // Store interpolation date
  294.             this.interpolationDate = interpolationDate;
  295.         }

  297.         /** Get interpolation date.
  298.          * @return interpolation date
  299.          */
  300.         public FieldAbsoluteDate<KK> getInterpolationDate() {
  301.             return interpolationDate;
  302.         }

  304.         /** Get neighbor list.
  305.          * @return neighbor list
  306.          */
  307.         public List<T> getNeighborList() {
  308.             return neighborList;
  309.         }

  311.         /** Get field.
  312.          * @return field
  313.          */
  314.         public Field<KK> getField() {
  315.             return field;
  316.         }

  318.         /** Get zero.
  319.          * @return zero
  320.          */
  321.         public KK getZero() {
  322.             return zero;
  323.         }

  325.         /** Get one.
  326.          * @return one
  327.          */
  328.         public KK getOne() {
  329.             return one;
  330.         }
  331.     }
  332. }
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