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.propagation.sampling;
18  
19  import org.orekit.frames.Frame;
20  import org.orekit.propagation.SpacecraftState;
21  import org.orekit.time.AbsoluteDate;
22  import org.orekit.utils.PVCoordinatesProvider;
23  import org.orekit.utils.TimeStampedPVCoordinates;
24  
25  /** This interface is a space-dynamics aware step interpolator.
26   *
27   * <p>It mirrors the <code>ODEStateInterpolator</code> interface from <a
28   * href="https://hipparchus.org/">Hipparchus</a> but
29   * provides a space-dynamics interface to the methods.</p>
30   * @author Luc Maisonobe
31   */
32  public interface OrekitStepInterpolator extends PVCoordinatesProvider {
33  
34      /**
35       * Get the state at previous grid point date.
36       * @return state at previous grid point date
37       */
38      SpacecraftState getPreviousState();
39  
40      /**
41       * Determines if the {@link #getPreviousState() previous state} is computed directly
42       * by the integrator, or if it is calculated using {@link #getInterpolatedState(AbsoluteDate)
43       * interpolation}.
44       *
45       * <p> Typically the previous state is directly computed by the integrator, but when
46       * events are detected the steps are shortened so that events occur on step boundaries
47       * which means the previous state may be computed by the interpolator.
48       *
49       * @return {@code true} if the previous state was calculated by the interpolator and
50       * false if it was computed directly by the integrator.
51       */
52      boolean isPreviousStateInterpolated();
53  
54      /**
55       * Get the state at current grid point date.
56       * @return state at current grid point date
57       */
58      SpacecraftState getCurrentState();
59  
60      /**
61       * Determines if the {@link #getCurrentState() current state} is computed directly by
62       * the integrator, or if it is calculated using {@link #getInterpolatedState(AbsoluteDate)
63       * interpolation}.
64       *
65       * <p> Typically the current state is directly computed by the integrator, but when
66       * events are detected the steps are shortened so that events occur on step boundaries
67       * which means the current state may be computed by the interpolator.
68       *
69       * @return {@code true} if the current state was calculated by the interpolator and
70       * false if it was computed directly by the integrator.
71       */
72      boolean isCurrentStateInterpolated();
73  
74      /** Get the state at interpolated date.
75       * @param date date of the interpolated state
76       * @return state at interpolated date
77       */
78      SpacecraftState getInterpolatedState(AbsoluteDate date);
79  
80      /** Check is integration direction is forward in date.
81       * @return true if integration is forward in date
82       */
83      boolean isForward();
84  
85      /** Create a new restricted version of the instance.
86       * <p>
87       * The instance is not changed at all.
88       * </p>
89       * @param newPreviousState start of the restricted step
90       * @param newCurrentState end of the restricted step
91       * @return restricted version of the instance
92       * @see #getPreviousState()
93       * @see #getCurrentState()
94       * @since 9.0
95       */
96      OrekitStepInterpolator restrictStep(SpacecraftState newPreviousState, SpacecraftState newCurrentState);
97  
98      /** {@inheritDoc}
99       * @since 12.0
100      */
101     @Override
102     default TimeStampedPVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame frame) {
103         return getInterpolatedState(date).getPVCoordinates(frame);
104     }
105 
106 }