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.forces.gravity.potential;
18  
19  import org.orekit.errors.OrekitException;
20  import org.orekit.errors.OrekitMessages;
21  import org.orekit.time.AbsoluteDate;
22  
23  /** Simple implementation of {@link RawSphericalHarmonicsProvider} for constant gravity fields.
24   * @author Luc Maisonobe
25   * @since 6.0
26   */
27  class ConstantSphericalHarmonics implements RawSphericalHarmonicsProvider {
28  
29      /** Central body reference radius. */
30      private final double ae;
31  
32      /** Central body attraction coefficient. */
33      private final double mu;
34  
35      /** Tide system. */
36      private final TideSystem tideSystem;
37  
38      /** Raw tesseral-sectorial coefficients matrix. */
39      private final double[][] rawC;
40  
41      /** Raw tesseral-sectorial coefficients matrix. */
42      private final double[][] rawS;
43  
44      /** Simple constructor.
45       * @param ae central body reference radius
46       * @param mu central body attraction coefficient
47       * @param tideSystem tide system
48       * @param rawC raw tesseral-sectorial coefficients
49       * @param rawS raw tesseral-sectorial coefficients
50       */
51      ConstantSphericalHarmonics(final double ae, final double mu,
52                                        final TideSystem tideSystem,
53                                        final double[][] rawC, final double[][] rawS) {
54          this.ae         = ae;
55          this.mu         = mu;
56          this.tideSystem = tideSystem;
57          this.rawC       = rawC;
58          this.rawS       = rawS;
59      }
60  
61      /** {@inheritDoc} */
62      public int getMaxDegree() {
63          return rawC.length - 1;
64      }
65  
66      /** {@inheritDoc} */
67      public int getMaxOrder() {
68          return rawC[rawC.length - 1].length - 1;
69      }
70  
71      /** {@inheritDoc} */
72      public double getMu() {
73          return mu;
74      }
75  
76      /** {@inheritDoc} */
77      public double getAe() {
78          return ae;
79      }
80  
81      /** {@inheritDoc}
82       * <p>
83       * For a constant field, null is always returned.
84       * </p>
85       */
86      public AbsoluteDate getReferenceDate() {
87          return null;
88      }
89  
90      /** {@inheritDoc} */
91      public double getOffset(final AbsoluteDate date) {
92          return 0.0;
93      }
94  
95      /** {@inheritDoc} */
96      public TideSystem getTideSystem() {
97          return tideSystem;
98      }
99  
100     @Override
101     public RawSphericalHarmonics onDate(final AbsoluteDate date) {
102         return new RawSphericalHarmonics() {
103 
104             @Override
105             public AbsoluteDate getDate() {
106                 return date;
107             }
108 
109             /** {@inheritDoc} */
110             public double getRawCnm(final int n, final int m) {
111                 checkLimits(n, m);
112                 return rawC[n][m];
113             }
114 
115             /** {@inheritDoc} */
116             public double getRawSnm(final int n, final int m) {
117                 checkLimits(n, m);
118                 return rawS[n][m];
119             }
120 
121         };
122     }
123 
124     /** Check limits.
125      * @param degree degree
126      * @param order order
127      */
128     private void checkLimits(final int degree, final int order) {
129 
130         if (degree >= rawC.length) {
131             throw new OrekitException(OrekitMessages.TOO_LARGE_DEGREE_FOR_GRAVITY_FIELD,
132                                       degree, rawC.length - 1);
133         }
134 
135         if (order >= rawC[degree].length) {
136             throw new OrekitException(OrekitMessages.TOO_LARGE_ORDER_FOR_GRAVITY_FIELD,
137                                       order, rawC[degree].length - 1);
138         }
139 
140     }
141 
142 }
143