1   /* Copyright 2002-2021 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.propagation.semianalytical.dsst.utilities;
18  
19  import org.hipparchus.Field;
20  import org.hipparchus.CalculusFieldElement;
21  import org.hipparchus.util.FastMath;
22  import org.hipparchus.util.MathArrays;
23  
24  /** Interpolation grid where points obey a maximum time gap.
25   * <p>
26   * The grid is adapted to the step considered,
27   * meaning that for short steps, the grid will have numerous points.
28   * </p>
29   *
30   * @author Luc Maisonobe
31   * @since 7.1
32   */
33  public class FieldMaxGapInterpolationGrid <T extends CalculusFieldElement<T>> implements FieldInterpolationGrid<T> {
34  
35      /** Maximum time gap. */
36      private final T maxGap;
37  
38      /** Field used by default. */
39      private final Field<T> field;
40  
41      /** Constructor.
42       * @param field field used by default
43       * @param maxGap maximum time gap between interpolation points
44       */
45      public FieldMaxGapInterpolationGrid(final Field<T> field, final T maxGap) {
46          this.field  = field;
47          this.maxGap = maxGap;
48      }
49  
50      /** {@inheritDoc} */
51      @Override
52      public T[] getGridPoints(final T stepStart, final T stepEnd) {
53          final int pointsPerStep = FastMath.max(2, (int) FastMath.ceil(FastMath.abs(stepEnd.getReal() - stepStart.getReal()) / maxGap.getReal()));;
54          final T[] grid = MathArrays.buildArray(field, pointsPerStep);
55  
56          final T stepSize = stepEnd.subtract(stepStart).divide(pointsPerStep - 1.);
57          for (int i = 0; i < pointsPerStep; i++) {
58              grid[i] = stepSize.multiply(i).add(stepStart);
59          }
60  
61          return grid;
62      }
63  }