1   /* Copyright 2022-2025 Romain Serra
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.events.functions;
18  
19  import org.hipparchus.CalculusFieldElement;
20  import org.hipparchus.util.FastMath;
21  import org.orekit.propagation.FieldSpacecraftState;
22  import org.orekit.propagation.SpacecraftState;
23  import org.orekit.time.TimeInterval;
24  
25  /**
26   * Class representing time interval crossing detection.
27   * It is positive within the interval.
28   * @author Romain Serra
29   * @since 14.0
30   */
31  public class TimeIntervalEventFunction implements EventFunction {
32  
33      /** Event interval. */
34      private final TimeInterval timeInterval;
35  
36      /**
37       * Constructor.
38       * @param timeInterval event crossing interval
39       */
40      public TimeIntervalEventFunction(final TimeInterval timeInterval) {
41          this.timeInterval = timeInterval;
42      }
43  
44      @Override
45      public double value(final SpacecraftState state) {
46          return FastMath.min(state.durationFrom(timeInterval.getStartDate()),
47                  -state.durationFrom(timeInterval.getEndDate()));
48      }
49  
50      @Override
51      public <T extends CalculusFieldElement<T>> T value(final FieldSpacecraftState<T> fieldState) {
52          return FastMath.min(fieldState.durationFrom(timeInterval.getStartDate()),
53                  fieldState.durationFrom(timeInterval.getEndDate()).negate());
54      }
55  
56      @Override
57      public boolean dependsOnTimeOnly() {
58          return true;
59      }
60  }