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;
18  
19  import org.hipparchus.analysis.interpolation.HermiteInterpolator;
20  
21  import java.util.List;
22  
23  /**
24   * Hermite interpolator of time stamped double value.
25   *
26   * @author Vincent Cucchietti
27   * @author Luc Maisonobe
28   * @see HermiteInterpolator
29   * @see TimeInterpolator
30   */
31  public class TimeStampedDoubleAndDerivativeHermiteInterpolator
32      extends AbstractTimeInterpolator<TimeStampedDoubleAndDerivative> {
33  
34      /**
35       * Constructor with :
36       * <ul>
37       *     <li>Default number of interpolation points of {@code DEFAULT_INTERPOLATION_POINTS}</li>
38       *     <li>Default extrapolation threshold value ({@code DEFAULT_EXTRAPOLATION_THRESHOLD_SEC} s)</li>
39       * </ul>
40       * As this implementation of interpolation is polynomial, it should be used only with small number of interpolation
41       * points (about 10-20 points) in order to avoid <a href="http://en.wikipedia.org/wiki/Runge%27s_phenomenon">Runge's
42       * phenomenon</a> and numerical problems (including NaN appearing).
43       */
44      public TimeStampedDoubleAndDerivativeHermiteInterpolator() {
45          this(DEFAULT_INTERPOLATION_POINTS);
46      }
47  
48      /**
49       * Constructor with default extrapolation threshold value ({@code DEFAULT_EXTRAPOLATION_THRESHOLD_SEC} s).
50       * <p>
51       * As this implementation of interpolation is polynomial, it should be used only with small number of interpolation
52       * points (about 10-20 points) in order to avoid <a href="http://en.wikipedia.org/wiki/Runge%27s_phenomenon">Runge's
53       * phenomenon</a> and numerical problems (including NaN appearing).
54       *
55       * @param interpolationPoints number of interpolation points
56       */
57      public TimeStampedDoubleAndDerivativeHermiteInterpolator(final int interpolationPoints) {
58          this(interpolationPoints, DEFAULT_EXTRAPOLATION_THRESHOLD_SEC);
59      }
60  
61      /**
62       * Constructor.
63       * <p>
64       * As this implementation of interpolation is polynomial, it should be used only with small number of interpolation
65       * points (about 10-20 points) in order to avoid <a href="http://en.wikipedia.org/wiki/Runge%27s_phenomenon">Runge's
66       * phenomenon</a> and numerical problems (including NaN appearing).
67       *
68       * @param interpolationPoints number of interpolation points
69       * @param extrapolationThreshold extrapolation threshold beyond which the propagation will fail
70       */
71      public TimeStampedDoubleAndDerivativeHermiteInterpolator(final int interpolationPoints, final double extrapolationThreshold) {
72          super(interpolationPoints, extrapolationThreshold);
73      }
74  
75      /** {@inheritDoc} */
76      @Override
77      protected TimeStampedDoubleAndDerivative interpolate(final InterpolationData interpolationData) {
78          final HermiteInterpolator interpolator = new HermiteInterpolator();
79  
80          // Fill interpolator with sample
81          final AbsoluteDate                         interpolationDate = interpolationData.getInterpolationDate();
82          final List<TimeStampedDoubleAndDerivative> neighborList      = interpolationData.getNeighborList();
83          for (TimeStampedDoubleAndDerivative value : neighborList) {
84              final double deltaT = value.getDate().durationFrom(interpolationDate);
85              interpolator.addSamplePoint(deltaT,
86                                          new double[] { value.getValue() },
87                                          new double[] { value.getDerivative() });
88          }
89  
90          final double[][] y = interpolator.derivatives(0, 1);
91          return new TimeStampedDoubleAndDerivative(y[0][0], y[1][0], interpolationDate);
92      }
93  
94  }