AngularAzEl.java

  1. /* Copyright 2002-2018 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.hipparchus.util.MathUtils;
  28. import org.orekit.errors.OrekitException;
  29. import org.orekit.frames.FieldTransform;
  30. import org.orekit.propagation.SpacecraftState;
  31. import org.orekit.time.AbsoluteDate;
  32. import org.orekit.time.FieldAbsoluteDate;
  33. import org.orekit.utils.ParameterDriver;
  34. import org.orekit.utils.TimeStampedFieldPVCoordinates;
  35. import org.orekit.utils.TimeStampedPVCoordinates;

  37. /** Class modeling an Azimuth-Elevation measurement from a ground station.
  38.  * The motion of the spacecraft during the signal flight time is taken into
  39.  * account. The date of the measurement corresponds to the reception on
  40.  * ground of the reflected signal.
  41.  *
  42.  * @author Thierry Ceolin
  43.  * @since 8.0
  44.  */
  45. public class AngularAzEl extends AbstractMeasurement<AngularAzEl> {

  47.     /** Ground station from which measurement is performed. */
  48.     private final GroundStation station;

  50.     /** Simple constructor.
  51.      * <p>
  52.      * This constructor uses 0 as the index of the propagator related
  53.      * to this measurement, thus being well suited for mono-satellite
  54.      * orbit determination.
  55.      * </p>
  56.      * @param station ground station from which measurement is performed
  57.      * @param date date of the measurement
  58.      * @param angular observed value
  59.      * @param sigma theoretical standard deviation
  60.      * @param baseWeight base weight
  61.      * @exception OrekitException if a {@link org.orekit.utils.ParameterDriver}
  62.      * name conflict occurs
  63.      */
  64.     public AngularAzEl(final GroundStation station, final AbsoluteDate date,
  65.                        final double[] angular, final double[] sigma, final double[] baseWeight)
  66.         throws OrekitException {
  67.         this(station, date, angular, sigma, baseWeight, 0);
  68.     }

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

  98.     /** Get the ground station from which measurement is performed.
  99.      * @return ground station from which measurement is performed
  100.      */
  101.     public GroundStation getStation() {
  102.         return station;
  103.     }

  105.     /** {@inheritDoc} */
  106.     @Override
  107.     protected EstimatedMeasurement<AngularAzEl> theoreticalEvaluation(final int iteration, final int evaluation,
  108.                                                                       final SpacecraftState[] states)
  109.         throws OrekitException {

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

  113.         // Azimuth/elevation derivatives are computed with respect to spacecraft state in inertial frame
  114.         // and station parameters
  115.         // ----------------------
  116.         //
  117.         // Parameters:
  118.         //  - 0..2 - Position of the spacecraft in inertial frame
  119.         //  - 3..5 - Velocity of the spacecraft in inertial frame
  120.         //  - 6..n - station parameters (station offsets, pole, prime meridian...)

  122.         // Get the number of parameters used for derivation
  123.         // Place the selected drivers into a map
  124.         int nbParams = 6;
  125.         final Map<String, Integer> indices = new HashMap<>();
  126.         for (ParameterDriver driver : getParametersDrivers()) {
  127.             if (driver.isSelected()) {
  128.                 indices.put(driver.getName(), nbParams++);
  129.             }
  130.         }
  131.         final DSFactory                          factory = new DSFactory(nbParams, 1);
  132.         final Field<DerivativeStructure>         field   = factory.getDerivativeField();
  133.         final FieldVector3D<DerivativeStructure> zero    = FieldVector3D.getZero(field);

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

  138.         // Transform between station and inertial frame, expressed as a derivative structure
  139.         // The components of station's position in offset frame are the 3 last derivative parameters
  140.         final AbsoluteDate downlinkDate = getDate();
  141.         final FieldAbsoluteDate<DerivativeStructure> downlinkDateDS =
  142.                         new FieldAbsoluteDate<>(field, downlinkDate);
  143.         final FieldTransform<DerivativeStructure> offsetToInertialDownlink =
  144.                         station.getOffsetToInertial(state.getFrame(), downlinkDateDS, factory, indices);

  146.         // Station position/velocity in inertial frame at end of the downlink leg
  147.         final TimeStampedFieldPVCoordinates<DerivativeStructure> stationDownlink =
  148.                         offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
  149.                                                                                                             zero, zero, zero));
  150.         // Station topocentric frame (east-north-zenith) in inertial frame expressed as DerivativeStructures
  151.         final FieldVector3D<DerivativeStructure> east   = offsetToInertialDownlink.transformVector(FieldVector3D.getPlusI(field));
  152.         final FieldVector3D<DerivativeStructure> north  = offsetToInertialDownlink.transformVector(FieldVector3D.getPlusJ(field));
  153.         final FieldVector3D<DerivativeStructure> zenith = offsetToInertialDownlink.transformVector(FieldVector3D.getPlusK(field));

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

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

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

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

  170.         // Station-satellite vector expressed in inertial frame
  171.         final FieldVector3D<DerivativeStructure> staSat = transitStateDS.getPosition().subtract(stationDownlink.getPosition());

  173.         // Compute azimuth/elevation
  174.         final DerivativeStructure baseAzimuth = DerivativeStructure.atan2(staSat.dotProduct(east), staSat.dotProduct(north));
  175.         final double              twoPiWrap   = MathUtils.normalizeAngle(baseAzimuth.getReal(), getObservedValue()[0]) -
  176.                                                 baseAzimuth.getReal();
  177.         final DerivativeStructure azimuth     = baseAzimuth.add(twoPiWrap);
  178.         final DerivativeStructure elevation   = staSat.dotProduct(zenith).divide(staSat.getNorm()).asin();

  180.         // Prepare the estimation
  181.         final EstimatedMeasurement<AngularAzEl> estimated =
  182.                         new EstimatedMeasurement<>(this, iteration, evaluation,
  183.                                                    new SpacecraftState[] {
  184.                                                        transitState
  185.                                                    }, new TimeStampedPVCoordinates[] {
  186.                                                        transitStateDS.toTimeStampedPVCoordinates(),
  187.                                                        stationDownlink.toTimeStampedPVCoordinates()
  188.                                                    });

  190.         // azimuth - elevation values
  191.         estimated.setEstimatedValue(azimuth.getValue(), elevation.getValue());

  193.         // Partial derivatives of azimuth/elevation with respect to state
  194.         // (beware element at index 0 is the value, not a derivative)
  195.         final double[] azDerivatives = azimuth.getAllDerivatives();
  196.         final double[] elDerivatives = elevation.getAllDerivatives();
  197.         estimated.setStateDerivatives(0,
  198.                                       Arrays.copyOfRange(azDerivatives, 1, 7), Arrays.copyOfRange(elDerivatives, 1, 7));

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

  209.         return estimated;
  210.     }
  211. }
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