1   /* Copyright 2002-2019 CS Systèmes d'Information
2    * Licensed to CS Systèmes d'Information (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.estimation.measurements;
18  
19  import org.hipparchus.util.FastMath;
20  import org.orekit.utils.ParameterDriver;
21  
22  /** Class modeling a satellite that can be observed.
23   *
24   * @author Luc Maisonobe
25   * @since 9.3
26   */
27  public class ObservableSatellite {
28  
29      /** Prefix for clock offset parameter driver, the propagator index will be appended to it. */
30      public static final String CLOCK_OFFSET_PREFIX = "clock-offset-satellite-";
31  
32      /** Clock offset scaling factor.
33       * <p>
34       * We use a power of 2 to avoid numeric noise introduction
35       * in the multiplications/divisions sequences.
36       * </p>
37       */
38      private static final double CLOCK_OFFSET_SCALE = FastMath.scalb(1.0, -10);
39  
40      /** Index of the propagator related to this satellite. */
41      private final int propagatorIndex;
42  
43      /** Parameter driver for satellite clock offset. */
44      private final ParameterDriver clockOffsetDriver;
45  
46      /** Simple constructor.
47       * @param propagatorIndex index of the propagator related to this satellite
48       */
49      public ObservableSatellite(final int propagatorIndex) {
50          this.propagatorIndex   = propagatorIndex;
51          this.clockOffsetDriver = new ParameterDriver(CLOCK_OFFSET_PREFIX + propagatorIndex,
52                                                       0.0, CLOCK_OFFSET_SCALE,
53                                                       Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
54      }
55  
56      /** Get the index of the propagator related to this satellite.
57       * @return index of the propagator related to this satellite
58       */
59      public int getPropagatorIndex() {
60          return propagatorIndex;
61      }
62  
63      /** Get the clock offset parameter driver.
64       * <p>
65       * The offset value is defined as the value in seconds that must be <em>subtracted</em> from
66       * the satellite clock reading of time to compute the real physical date. The offset
67       * is therefore negative if the satellite clock is slow and positive if it is fast.
68       * </p>
69       * @return clock offset parameter driver
70       */
71      public ParameterDriver getClockOffsetDriver() {
72          return clockOffsetDriver;
73      }
74  
75  }