InterpolatingTransformProvider.java

/* Copyright 2002-2025 CS GROUP
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 * 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,
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package org.orekit.frames;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import org.hipparchus.Field;
import org.hipparchus.CalculusFieldElement;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.AngularDerivativesFilter;
import org.orekit.utils.CartesianDerivativesFilter;
import org.orekit.utils.GenericTimeStampedCache;

/** Transform provider using thread-safe interpolation on transforms sample.
 * <p>
 * The interpolation is a polynomial Hermite interpolation, which
 * can either use or ignore the derivatives provided by the raw
 * provider. This means that simple raw providers that do not compute
 * derivatives can be used, the derivatives will be added appropriately
 * by the interpolation process.
 * </p>
 * @see GenericTimeStampedCache
 * @see ShiftingTransformProvider
 * @author Luc Maisonobe
 */
public class InterpolatingTransformProvider implements TransformProvider {

    /** Provider for raw (non-interpolated) transforms. */
    private final TransformProvider rawProvider;

    /** Filter for Cartesian derivatives to use in interpolation. */
    private final CartesianDerivativesFilter cFilter;

    /** Filter for angular derivatives to use in interpolation. */
    private final AngularDerivativesFilter aFilter;

    /** Grid points time step. */
    private final double step;

    /** Cache for sample points. */
    private final transient GenericTimeStampedCache<Transform> cache;

    /** Field caches for sample points. */
    // we use Object as the value of fieldCaches because despite numerous attempts,
    // we could not find a way to use GenericTimeStampedCache<FieldTransform<? extends CalculusFieldElement<?>>
    // without the compiler complaining
    private final transient Map<Field<? extends CalculusFieldElement<?>>, Object> fieldCaches;

    /** Simple constructor.
     * @param rawProvider provider for raw (non-interpolated) transforms
     * @param cFilter filter for derivatives from the sample to use in interpolation
     * @param aFilter filter for derivatives from the sample to use in interpolation
     * @param gridPoints number of interpolation grid points
     * @param step grid points time step
     * @param maxSlots maximum number of independent cached time slots
     * in the {@link GenericTimeStampedCache time-stamped cache}
     * @param maxSpan maximum duration span in seconds of one slot
     * in the {@link GenericTimeStampedCache time-stamped cache}
     * @param newSlotInterval time interval above which a new slot is created
     * in the {@link GenericTimeStampedCache time-stamped cache}
     * @since 9.1
     */
    public InterpolatingTransformProvider(final TransformProvider rawProvider,
                                          final CartesianDerivativesFilter cFilter,
                                          final AngularDerivativesFilter aFilter,
                                          final int gridPoints, final double step,
                                          final int maxSlots, final double maxSpan, final double newSlotInterval) {
        this.rawProvider = rawProvider;
        this.cFilter     = cFilter;
        this.aFilter     = aFilter;
        this.step        = step;
        this.cache       = new GenericTimeStampedCache<>(gridPoints, maxSlots, maxSpan, newSlotInterval,
                new TransformGenerator(gridPoints,
                        rawProvider,
                        step));
        this.fieldCaches = new HashMap<>();
    }

    /** Get the underlying provider for raw (non-interpolated) transforms.
     * @return provider for raw (non-interpolated) transforms
     */
    public TransformProvider getRawProvider() {
        return rawProvider;
    }

    /** Get the number of interpolation grid points.
     * @return number of interpolation grid points
     */
    public int getGridPoints() {
        return cache.getMaxNeighborsSize();
    }

    /** Get the grid points time step.
     * @return grid points time step
     */
    public double getStep() {
        return step;
    }

    /** {@inheritDoc} */
    @Override
    public Transform getTransform(final AbsoluteDate date) {
        // retrieve a sample from the thread-safe cache
        final List<Transform> sample = cache.getNeighbors(date).collect(Collectors.toList());

        // interpolate to specified date
        return Transform.interpolate(date, cFilter, aFilter, sample);
    }

    /** {@inheritDoc} */
    @Override
    public <T extends CalculusFieldElement<T>> FieldTransform<T> getTransform(final FieldAbsoluteDate<T> date) {
        @SuppressWarnings("unchecked")
        GenericTimeStampedCache<FieldTransform<T>> fieldCache =
            (GenericTimeStampedCache<FieldTransform<T>>) fieldCaches.get(date.getField());
        if (fieldCache == null) {
            fieldCache =
                    new GenericTimeStampedCache<>(cache.getMaxNeighborsSize(),
                            cache.getMaxSlots(),
                            cache.getMaxSpan(),
                            cache.getNewSlotQuantumGap(),
                            new FieldTransformGenerator<>(date.getField(),
                                    cache.getMaxNeighborsSize(),
                                    rawProvider,
                                    step));
            fieldCaches.put(date.getField(), fieldCache);
        }

        // retrieve a sample from the thread-safe cache
        final Stream<FieldTransform<T>> sample = fieldCache.getNeighbors(date.toAbsoluteDate());

        // interpolate to specified date
        return FieldTransform.interpolate(date, cFilter, aFilter, sample);
    }

}