1   /* Copyright 2013-2019 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.rugged.los;
18  
19  import java.util.stream.Stream;
20  
21  import org.hipparchus.analysis.differentiation.DerivativeStructure;
22  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
23  import org.hipparchus.geometry.euclidean.threed.Vector3D;
24  import org.hipparchus.util.FastMath;
25  import org.orekit.rugged.utils.DSGenerator;
26  import org.orekit.utils.ParameterDriver;
27  import org.orekit.utils.ParameterObserver;
28  
29  /** {@link TimeIndependentLOSTransform LOS transform} based on a homothety along the Z axis.
30   * @author Lucie Labatallee
31   * @author Guylaine Prat
32   * @see LOSBuilder
33   * @since 2.0
34   */
35  public class FixedZHomothety implements TimeIndependentLOSTransform {
36  
37      /** Parameters scaling factor.
38       * <p>
39       * We use a power of 2 to avoid numeric noise introduction
40       * in the multiplications/divisions sequences.
41       * </p>
42       */
43      private final double SCALE = FastMath.scalb(1.0, 0);
44  
45      /** Homothety factor. */
46      private double factor;
47  
48      /** Underlying homothety with derivatives. */
49      private DerivativeStructure factorDS;
50  
51      /** Driver for homothety factor. */
52      private final ParameterDriver factorDriver;
53  
54      /** Simple constructor.
55       * <p>
56       * The single parameter is the homothety factor.
57       * </p>
58       * @param name name of the homothety (used for estimated parameters identification)
59       * @param factorvalue homothety factor
60       */
61      public FixedZHomothety(final String name, final double factorvalue) {
62  
63          this.factor   = factorvalue;
64          this.factorDS = null;
65          this.factorDriver = new ParameterDriver(name, factorvalue, SCALE, 0, Double.POSITIVE_INFINITY);
66          factorDriver.addObserver(new ParameterObserver() {
67              @Override
68              public void valueChanged(final double previousValue, final ParameterDriver driver) {
69                  // reset factor to zero, they will be evaluated lazily if needed
70                  factor = 0.0;
71                  factorDS = null;
72              }
73          });
74      }
75  
76      /** {@inheritDoc} */
77      @Override
78      public Stream<ParameterDriver> getParametersDrivers() {
79          return Stream.of(factorDriver);
80      }
81  
82      /** {@inheritDoc} */
83      @Override
84      public Vector3D transformLOS(final int i, final Vector3D los) {
85  
86          if (factor == 0.0) {
87              // lazy evaluation of the homothety
88              factor = factorDriver.getValue();
89          }
90          return new Vector3D(los.getX(), los.getY(), factor * los.getZ());
91      }
92  
93      /** {@inheritDoc} */
94      @Override
95      public FieldVector3D<DerivativeStructure> transformLOS(final int i, final FieldVector3D<DerivativeStructure> los,
96                                                             final DSGenerator generator) {
97          if (factorDS == null) {
98              // lazy evaluation of the homothety
99              factorDS = generator.variable(factorDriver);
100         }
101         return new FieldVector3D<DerivativeStructure>(los.getX(), los.getY(), factorDS.multiply(los.getZ()));
102     }
103 
104 }