Range.java

  1. /* Copyright 2002-2017 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;

  19. import java.util.Arrays;
  20. import java.util.HashMap;
  21. import java.util.Map;

  23. import org.hipparchus.Field;
  24. import org.hipparchus.analysis.differentiation.DSFactory;
  25. import org.hipparchus.analysis.differentiation.DerivativeStructure;
  26. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  27. import org.orekit.errors.OrekitException;
  28. import org.orekit.frames.FieldTransform;
  29. import org.orekit.propagation.SpacecraftState;
  30. import org.orekit.time.AbsoluteDate;
  31. import org.orekit.time.FieldAbsoluteDate;
  32. import org.orekit.utils.Constants;
  33. import org.orekit.utils.ParameterDriver;
  34. import org.orekit.utils.TimeStampedFieldPVCoordinates;
  35. import org.orekit.utils.TimeStampedPVCoordinates;

  37. /** Class modeling a range measurement from a ground station.
  38.  * <p>
  39.  * The measurement is considered to be a signal emitted from
  40.  * a ground station, reflected on spacecraft, and received
  41.  * on the same ground station. Its value is the elapsed time
  42.  * between emission and reception divided by 2c were c is the
  43.  * speed of light. The motion of both the station and the
  44.  * spacecraft during the signal flight time are taken into
  45.  * account. The date of the measurement corresponds to the
  46.  * reception on ground of the reflected signal.
  47.  * </p>
  48.  * @author Thierry Ceolin
  49.  * @author Luc Maisonobe
  50.  * @author Maxime Journot
  51.  * @since 8.0
  52.  */
  53. public class Range extends AbstractMeasurement<Range> {

  55.     /** Ground station from which measurement is performed. */
  56.     private final GroundStation station;

  58.     /** Simple constructor.
  59.      * <p>
  60.      * This constructor uses 0 as the index of the propagator related
  61.      * to this measurement, thus being well suited for mono-satellite
  62.      * orbit determination.
  63.      * </p>
  64.      * @param station ground station from which measurement is performed
  65.      * @param date date of the measurement
  66.      * @param range observed value
  67.      * @param sigma theoretical standard deviation
  68.      * @param baseWeight base weight
  69.      * @exception OrekitException if a {@link org.orekit.utils.ParameterDriver}
  70.      * name conflict occurs
  71.      */
  72.     public Range(final GroundStation station, final AbsoluteDate date,
  73.                  final double range, final double sigma, final double baseWeight)
  74.         throws OrekitException {
  75.         this(station, date, range, sigma, baseWeight, 0);
  76.     }

  78.     /** Simple constructor.
  79.      * @param station ground station from which measurement is performed
  80.      * @param date date of the measurement
  81.      * @param range observed value
  82.      * @param sigma theoretical standard deviation
  83.      * @param baseWeight base weight
  84.      * @param propagatorIndex index of the propagator related to this measurement
  85.      * @exception OrekitException if a {@link org.orekit.utils.ParameterDriver}
  86.      * name conflict occurs
  87.      * @since 9.0
  88.      */
  89.     public Range(final GroundStation station, final AbsoluteDate date,
  90.                  final double range, final double sigma, final double baseWeight,
  91.                  final int propagatorIndex)
  92.         throws OrekitException {
  93.         super(date, range, sigma, baseWeight, Arrays.asList(propagatorIndex),
  94.               station.getEastOffsetDriver(),
  95.               station.getNorthOffsetDriver(),
  96.               station.getZenithOffsetDriver(),
  97.               station.getPrimeMeridianOffsetDriver(),
  98.               station.getPrimeMeridianDriftDriver(),
  99.               station.getPolarOffsetXDriver(),
  100.               station.getPolarDriftXDriver(),
  101.               station.getPolarOffsetYDriver(),
  102.               station.getPolarDriftYDriver());
  103.         this.station = station;
  104.     }

  106.     /** Get the ground station from which measurement is performed.
  107.      * @return ground station from which measurement is performed
  108.      */
  109.     public GroundStation getStation() {
  110.         return station;
  111.     }

  113.     /** {@inheritDoc} */
  114.     @Override
  115.     protected EstimatedMeasurement<Range> theoreticalEvaluation(final int iteration,
  116.                                                                 final int evaluation,
  117.                                                                 final SpacecraftState[] states)
  118.         throws OrekitException {

  120.         final SpacecraftState state = states[getPropagatorsIndices().get(0)];

  122.         // Range derivatives are computed with respect to spacecraft state in inertial frame
  123.         // and station parameters
  124.         // ----------------------
  125.         //
  126.         // Parameters:
  127.         //  - 0..2 - Position of the spacecraft in inertial frame
  128.         //  - 3..5 - Velocity of the spacecraft in inertial frame
  129.         //  - 6..n - station parameters (station offsets, pole, prime meridian...)
  130.         int nbParams = 6;
  131.         final Map<String, Integer> indices = new HashMap<>();
  132.         for (ParameterDriver driver : getParametersDrivers()) {
  133.             if (driver.isSelected()) {
  134.                 indices.put(driver.getName(), nbParams++);
  135.             }
  136.         }
  137.         final DSFactory                          factory = new DSFactory(nbParams, 1);
  138.         final Field<DerivativeStructure>         field   = factory.getDerivativeField();
  139.         final FieldVector3D<DerivativeStructure> zero    = FieldVector3D.getZero(field);

  141.         // Coordinates of the spacecraft expressed as a derivative structure
  142.         final TimeStampedFieldPVCoordinates<DerivativeStructure> pvaDS = getCoordinates(state, 0, factory);

  144.         // transform between station and inertial frame, expressed as a derivative structure
  145.         // The components of station's position in offset frame are the 3 last derivative parameters
  146.         final AbsoluteDate downlinkDate = getDate();
  147.         final FieldAbsoluteDate<DerivativeStructure> downlinkDateDS =
  148.                         new FieldAbsoluteDate<>(field, downlinkDate);
  149.         final FieldTransform<DerivativeStructure> offsetToInertialDownlink =
  150.                         station.getOffsetToInertial(state.getFrame(), downlinkDateDS, factory, indices);

  152.         // Station position in inertial frame at end of the downlink leg
  153.         final TimeStampedFieldPVCoordinates<DerivativeStructure> stationDownlink =
  154.                         offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
  155.                                                                                                             zero, zero, zero));

  157.         // Compute propagation times
  158.         // (if state has already been set up to pre-compensate propagation delay,
  159.         //  we will have delta == tauD and transitState will be the same as state)

  161.         // Downlink delay
  162.         final DerivativeStructure tauD = signalTimeOfFlight(pvaDS, stationDownlink.getPosition(), downlinkDateDS);

  164.         // Transit state
  165.         final double                delta        = downlinkDate.durationFrom(state.getDate());
  166.         final DerivativeStructure   deltaMTauD   = tauD.negate().add(delta);
  167.         final SpacecraftState       transitState = state.shiftedBy(deltaMTauD.getValue());

  169.         // Transit state (re)computed with derivative structures
  170.         final TimeStampedFieldPVCoordinates<DerivativeStructure> transitStateDS = pvaDS.shiftedBy(deltaMTauD);

  172.         // Station at transit state date (derivatives of tauD taken into account)
  173.         final TimeStampedFieldPVCoordinates<DerivativeStructure> stationAtTransitDate =
  174.                         stationDownlink.shiftedBy(tauD.negate());

  176.         // Uplink delay
  177.         final DerivativeStructure tauU =
  178.                         signalTimeOfFlight(stationAtTransitDate, transitStateDS.getPosition(), transitStateDS.getDate());
  179.         final TimeStampedFieldPVCoordinates<DerivativeStructure> stationUplink =
  180.                         stationDownlink.shiftedBy(-tauD.getValue() - tauU.getValue());

  182.         // Prepare the evaluation
  183.         final EstimatedMeasurement<Range> estimated =
  184.                         new EstimatedMeasurement<Range>(this, iteration, evaluation,
  185.                                                         new SpacecraftState[] {
  186.                                                             transitState
  187.                                                         }, new TimeStampedPVCoordinates[] {
  188.                                                             stationUplink.toTimeStampedPVCoordinates(),
  189.                                                             transitStateDS.toTimeStampedPVCoordinates(),
  190.                                                             stationDownlink.toTimeStampedPVCoordinates()
  191.                                                         });

  193.         // Range value
  194.         final double              cOver2 = 0.5 * Constants.SPEED_OF_LIGHT;
  195.         final DerivativeStructure tau    = tauD.add(tauU);
  196.         final DerivativeStructure range  = tau.multiply(cOver2);
  197.         estimated.setEstimatedValue(range.getValue());

  199.         // Range partial derivatives with respect to state
  200.         final double[] derivatives = range.getAllDerivatives();
  201.         estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 1, 7));

  203.         // set partial derivatives with respect to parameters
  204.         // (beware element at index 0 is the value, not a derivative)
  205.         for (final ParameterDriver driver : getParametersDrivers()) {
  206.             final Integer index = indices.get(driver.getName());
  207.             if (index != null) {
  208.                 estimated.setParameterDerivatives(driver, derivatives[index + 1]);
  209.             }
  210.         }

  212.         return estimated;

  214.     }

  216. }
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