1   /* Copyright 2022-2026 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.orekit.bodies.BodyShape;
21  import org.orekit.propagation.FieldSpacecraftState;
22  import org.orekit.propagation.SpacecraftState;
23  
24  /** Class for geodetic altitude value-crossing event function.
25   * It is negative under the critical value.
26   * @author Romain Serra
27   * @since 14.0
28   */
29  public class AltitudeEventFunction extends AbstractGeodeticEventFunction {
30  
31      /** Critical altitude for crossing event. */
32      private final double criticalAltitude;
33  
34      /** Constructor.
35       * @param body body
36       * @param criticalAltitude altitude for crossing
37       */
38      public AltitudeEventFunction(final BodyShape body, final double criticalAltitude) {
39          super(body);
40          this.criticalAltitude = criticalAltitude;
41      }
42  
43      @Override
44      public double value(final SpacecraftState state) {
45          return transformToGeodeticPoint(state).getAltitude() - criticalAltitude;
46      }
47  
48      @Override
49      public <T extends CalculusFieldElement<T>> T value(final FieldSpacecraftState<T> fieldState) {
50          return transformToGeodeticPoint(fieldState).getAltitude().subtract(criticalAltitude);
51      }
52  }