AbstractTimeInterpolator.java
/* Copyright 2002-2023 CS GROUP
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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*/
package org.orekit.time;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitIllegalArgumentException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.errors.OrekitMessages;
import org.orekit.utils.ImmutableTimeStampedCache;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.Stream;
/**
* Abstract class for time interpolator.
*
* @param <T> interpolated time stamped type
*
* @author Vincent Cucchietti
*/
public abstract class AbstractTimeInterpolator<T extends TimeStamped> implements TimeInterpolator<T> {
/** Default extrapolation time threshold: 1ms. */
public static final double DEFAULT_EXTRAPOLATION_THRESHOLD_SEC = 1e-3;
/** Default number of interpolation points. */
public static final int DEFAULT_INTERPOLATION_POINTS = 2;
/** The extrapolation threshold beyond which the propagation will fail. */
private final double extrapolationThreshold;
/** Neighbor size. */
private final int interpolationPoints;
/**
* Constructor.
*
* @param interpolationPoints number of interpolation points
* @param extrapolationThreshold extrapolation threshold beyond which the propagation will fail
*/
public AbstractTimeInterpolator(final int interpolationPoints, final double extrapolationThreshold) {
this.interpolationPoints = interpolationPoints;
this.extrapolationThreshold = extrapolationThreshold;
}
/**
* Method checking if given interpolator is compatible with given sample size.
*
* @param interpolator interpolator
* @param sampleSize sample size
*/
public static void checkInterpolatorCompatibilityWithSampleSize(
final TimeInterpolator<? extends TimeStamped> interpolator,
final int sampleSize) {
// Retrieve all sub-interpolators (or a singleton list with given interpolator if there are no sub-interpolators)
final List<TimeInterpolator<? extends TimeStamped>> subInterpolators = interpolator.getSubInterpolators();
for (final TimeInterpolator<? extends TimeStamped> subInterpolator : subInterpolators) {
if (sampleSize < subInterpolator.getNbInterpolationPoints()) {
throw new OrekitIllegalArgumentException(OrekitMessages.NOT_ENOUGH_DATA, sampleSize);
}
}
}
/** {@inheritDoc} */
@Override
public T interpolate(final AbsoluteDate interpolationDate, final Stream<T> sample) {
return interpolate(interpolationDate, sample.collect(Collectors.toList()));
}
/** {@inheritDoc}. */
@Override
public T interpolate(final AbsoluteDate interpolationDate, final Collection<T> sample) {
final InterpolationData interpolationData = new InterpolationData(interpolationDate, sample);
return interpolate(interpolationData);
}
/**
* Get the central date to use to find neighbors while taking into account extrapolation threshold.
*
* @param date interpolation date
* @param cachedSamples cached samples
* @param threshold extrapolation threshold
* @param <T> type of element
*
* @return central date to use to find neighbors
* @since 12.0.1
*/
public static <T extends TimeStamped> AbsoluteDate getCentralDate(final AbsoluteDate date,
final ImmutableTimeStampedCache<T> cachedSamples,
final double threshold) {
final AbsoluteDate central;
final AbsoluteDate minDate = cachedSamples.getEarliest().getDate();
final AbsoluteDate maxDate = cachedSamples.getLatest().getDate();
if (date.compareTo(minDate) < 0 && FastMath.abs(date.durationFrom(minDate)) <= threshold) {
// avoid TimeStampedCacheException as we are still within the tolerance before minDate
central = minDate;
} else if (date.compareTo(maxDate) > 0 && FastMath.abs(date.durationFrom(maxDate)) <= threshold) {
// avoid TimeStampedCacheException as we are still within the tolerance after maxDate
central = maxDate;
} else {
central = date;
}
return central;
}
/** {@inheritDoc} */
public List<TimeInterpolator<? extends TimeStamped>> getSubInterpolators() {
return Collections.singletonList(this);
}
/** {@inheritDoc} */
public int getNbInterpolationPoints() {
final List<TimeInterpolator<? extends TimeStamped>> subInterpolators = getSubInterpolators();
// In case the interpolator does not have sub interpolators
if (subInterpolators.size() == 1) {
return interpolationPoints;
}
// Otherwise find maximum number of interpolation points among sub interpolators
else {
final Optional<Integer> optionalMaxNbInterpolationPoints =
subInterpolators.stream().map(TimeInterpolator::getNbInterpolationPoints).max(Integer::compareTo);
if (optionalMaxNbInterpolationPoints.isPresent()) {
return optionalMaxNbInterpolationPoints.get();
} else {
// This should never happen
throw new OrekitInternalError(null);
}
}
}
/** {@inheritDoc} */
public double getExtrapolationThreshold() {
return extrapolationThreshold;
}
/**
* Add all lowest level sub interpolators to the sub interpolator list.
*
* @param subInterpolator optional sub interpolator to add
* @param subInterpolators list of sub interpolators
*/
protected void addOptionalSubInterpolatorIfDefined(final TimeInterpolator<? extends TimeStamped> subInterpolator,
final List<TimeInterpolator<? extends TimeStamped>> subInterpolators) {
// Add all lowest level sub interpolators
if (subInterpolator != null) {
subInterpolators.addAll(subInterpolator.getSubInterpolators());
}
}
/**
* Interpolate instance from given interpolation data.
*
* @param interpolationData interpolation data
*
* @return interpolated instance from given interpolation data.
*/
protected abstract T interpolate(InterpolationData interpolationData);
/**
* Get the time parameter which lies between [0:1] by normalizing the difference between interpolating time and previous
* date by the Δt between tabulated values.
*
* @param interpolatingTime time at which we want to interpolate a value (between previous and next tabulated dates)
* @param previousDate previous tabulated value date
* @param nextDate next tabulated value date
*
* @return time parameter which lies between [0:1]
*/
protected double getTimeParameter(final AbsoluteDate interpolatingTime,
final AbsoluteDate previousDate,
final AbsoluteDate nextDate) {
return interpolatingTime.durationFrom(previousDate) / nextDate.getDate().durationFrom(previousDate);
}
/**
* Nested class used to store interpolation data.
* <p>
* It makes the interpolator thread safe.
*/
public class InterpolationData {
/** Interpolation date. */
private final AbsoluteDate interpolationDate;
/** Cached samples. */
private final ImmutableTimeStampedCache<T> cachedSamples;
/** Neighbor list around interpolation date. */
private final List<T> neighborList;
/**
* Constructor.
*
* @param interpolationDate interpolation date
* @param sample time stamped sample
*/
protected InterpolationData(final AbsoluteDate interpolationDate, final Collection<T> sample) {
// Handle specific case that is not handled by the immutable time stamped cache constructor
if (sample.size() < 2) {
throw new OrekitIllegalArgumentException(OrekitMessages.NOT_ENOUGH_DATA, sample.size());
}
// Create immutable time stamped cache
this.cachedSamples = new ImmutableTimeStampedCache<>(interpolationPoints, sample);
// Find neighbors
final AbsoluteDate central = getCentralDate(interpolationDate);
final Stream<T> neighborsStream = cachedSamples.getNeighbors(central);
// Convert to unmodifiable list
this.neighborList = Collections.unmodifiableList(neighborsStream.collect(Collectors.toList()));
// Store interpolation date
this.interpolationDate = interpolationDate;
}
/**
* Get the central date to use to find neighbors while taking into account extrapolation threshold.
*
* @param date interpolation date
*
* @return central date to use to find neighbors
*/
protected AbsoluteDate getCentralDate(final AbsoluteDate date) {
return AbstractTimeInterpolator.getCentralDate(date, cachedSamples, extrapolationThreshold);
}
/** Get interpolation date.
* @return interpolation date
*/
public AbsoluteDate getInterpolationDate() {
return interpolationDate;
}
/** Get cached samples.
* @return cached samples
*/
public ImmutableTimeStampedCache<T> getCachedSamples() {
return cachedSamples;
}
/** Get neighbor list.
* @return neighbor list
*/
public List<T> getNeighborList() {
return neighborList;
}
}
}