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.estimation.measurements.modifiers;
18  
19  import org.hipparchus.geometry.euclidean.threed.Vector3D;
20  import org.hipparchus.util.FastMath;
21  import org.orekit.estimation.measurements.EstimatedMeasurement;
22  import org.orekit.utils.Constants;
23  import org.orekit.utils.TimeStampedPVCoordinates;
24  
25  /** Class modifying theoretical range measurement with Shapiro time delay.
26   * <p>
27   * Shapiro time delay is a relativistic effect due to gravity.
28   * </p>
29   *
30   * @author Luc Maisonobe
31   * @since 10.0
32   */
33  public class AbstractShapiroBaseModifier {
34  
35      /** Shapiro effect scale factor. */
36      private final double s;
37  
38      /** Simple constructor.
39       * @param gm gravitational constant for main body in signal path vicinity.
40       */
41      public AbstractShapiroBaseModifier(final double gm) {
42          this.s = 2 * gm / (Constants.SPEED_OF_LIGHT * Constants.SPEED_OF_LIGHT);
43      }
44  
45      /** Modify measurement.
46       * @param estimated measurement to modify
47       */
48      protected void doModify(final EstimatedMeasurement<?> estimated) {
49  
50          // compute correction, for one way or two way measurements
51          final TimeStampedPVCoordinates[] pv = estimated.getParticipants();
52          final double correction = pv.length < 3 ?
53                                    shapiroCorrection(pv[0], pv[1]) :
54                                    0.5 * (shapiroCorrection(pv[0], pv[1]) + shapiroCorrection(pv[1], pv[2]));
55  
56          // update estimated value taking into account the Shapiro time delay.
57          final double[] newValue = estimated.getEstimatedValue().clone();
58          newValue[0] = newValue[0] + correction;
59          estimated.setEstimatedValue(newValue);
60  
61      }
62  
63      /** Compute Shapiro path dilation between two points in a gravity field.
64       * @param pvEmitter coordinates of emitter in body-centered frame
65       * @param pvReceiver coordinates of receiver in body-centered frame
66       * @return path dilation to add to raw measurement
67       */
68      protected double shapiroCorrection(final TimeStampedPVCoordinates pvEmitter, final TimeStampedPVCoordinates pvReceiver) {
69          final Vector3D pEmitter  = pvEmitter.getPosition();
70          final Vector3D pReceiver = pvReceiver.getPosition();
71          final double   rEpR      = pEmitter.getNorm() + pReceiver.getNorm();
72          final double   d         = Vector3D.distance(pEmitter, pReceiver);
73          return s * FastMath.log((rEpR + d) / (rEpR - d));
74      }
75  
76  }