AngularRaDec.java

  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;

  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.frames.FieldTransform;
  29. import org.orekit.frames.Frame;
  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 Right Ascension - Declination measurement from a ground point (station, telescope).
  38.  * The angles are given in an inertial reference frame.
  39.  * The motion of the spacecraft during the signal flight time is taken into
  40.  * account. The date of the measurement corresponds to the reception on
  41.  * ground of the reflected signal.
  42.  *
  43.  * @author Thierry Ceolin
  44.  * @author Maxime Journot
  45.  * @since 9.0
  46.  */
  47. public class AngularRaDec extends AbstractMeasurement<AngularRaDec> {

  49.     /** Ground station from which measurement is performed. */
  50.     private final GroundStation station;

  52.     /** Reference frame in which the right ascension - declination angles are given. */
  53.     private final Frame referenceFrame;

  55.     /** Simple constructor.
  56.      * <p>
  57.      * This constructor uses 0 as the index of the propagator related
  58.      * to this measurement, thus being well suited for mono-satellite
  59.      * orbit determination.
  60.      * </p>
  61.      * @param station ground station from which measurement is performed
  62.      * @param referenceFrame Reference frame in which the right ascension - declination angles are given
  63.      * @param date date of the measurement
  64.      * @param angular observed value
  65.      * @param sigma theoretical standard deviation
  66.      * @param baseWeight base weight
  67.      * @deprecated since 9.3, replaced by {@link #AngularRaDec(GroundStation, Frame, AbsoluteDate,
  68.      * double[], double[], double[], ObservableSatellite)}
  69.      */
  70.     @Deprecated
  71.     public AngularRaDec(final GroundStation station, final Frame referenceFrame, final AbsoluteDate date,
  72.                         final double[] angular, final double[] sigma, final double[] baseWeight) {
  73.         this(station, referenceFrame, date, angular, sigma, baseWeight, new ObservableSatellite(0));
  74.     }

  76.     /** Simple constructor.
  77.      * @param station ground station from which measurement is performed
  78.      * @param referenceFrame Reference frame in which the right ascension - declination angles are given
  79.      * @param date date of the measurement
  80.      * @param angular observed value
  81.      * @param sigma theoretical standard deviation
  82.      * @param baseWeight base weight
  83.      * @param propagatorIndex index of the propagator related to this measurement
  84.      * @since 9.0
  85.      * @deprecated since 9.3, replaced by {@link #AngularRaDec(GroundStation, Frame, AbsoluteDate,
  86.      * double[], double[], double[], ObservableSatellite)}
  87.      */
  88.     @Deprecated
  89.     public AngularRaDec(final GroundStation station, final Frame referenceFrame, final AbsoluteDate date,
  90.                         final double[] angular, final double[] sigma, final double[] baseWeight,
  91.                         final int propagatorIndex) {
  92.         this(station, referenceFrame, date, angular, sigma, baseWeight, new ObservableSatellite(propagatorIndex));
  93.     }

  95.     /** Simple constructor.
  96.      * @param station ground station from which measurement is performed
  97.      * @param referenceFrame Reference frame in which the right ascension - declination angles are given
  98.      * @param date date of the measurement
  99.      * @param angular observed value
  100.      * @param sigma theoretical standard deviation
  101.      * @param baseWeight base weight
  102.      * @param satellite satellite related to this measurement
  103.      * @since 9.3
  104.      */
  105.     public AngularRaDec(final GroundStation station, final Frame referenceFrame, final AbsoluteDate date,
  106.                         final double[] angular, final double[] sigma, final double[] baseWeight,
  107.                         final ObservableSatellite satellite) {
  108.         super(date, angular, sigma, baseWeight, Arrays.asList(satellite));
  109.         addParameterDriver(station.getClockOffsetDriver());
  110.         addParameterDriver(station.getEastOffsetDriver());
  111.         addParameterDriver(station.getNorthOffsetDriver());
  112.         addParameterDriver(station.getZenithOffsetDriver());
  113.         addParameterDriver(station.getPrimeMeridianOffsetDriver());
  114.         addParameterDriver(station.getPrimeMeridianDriftDriver());
  115.         addParameterDriver(station.getPolarOffsetXDriver());
  116.         addParameterDriver(station.getPolarDriftXDriver());
  117.         addParameterDriver(station.getPolarOffsetYDriver());
  118.         addParameterDriver(station.getPolarDriftYDriver());
  119.         this.station        = station;
  120.         this.referenceFrame = referenceFrame;
  121.     }

  123.     /** Get the ground station from which measurement is performed.
  124.      * @return ground station from which measurement is performed
  125.      */
  126.     public GroundStation getStation() {
  127.         return station;
  128.     }

  130.     /** Get the reference frame in which the right ascension - declination angles are given.
  131.      * @return reference frame in which the right ascension - declination angles are given
  132.      */
  133.     public Frame getReferenceFrame() {
  134.         return referenceFrame;
  135.     }

  137.     /** {@inheritDoc} */
  138.     @Override
  139.     protected EstimatedMeasurement<AngularRaDec> theoreticalEvaluation(final int iteration, final int evaluation,
  140.                                                                        final SpacecraftState[] states) {

  142.         final ObservableSatellite satellite = getSatellites().get(0);
  143.         final SpacecraftState     state     = states[satellite.getPropagatorIndex()];

  145.         // Right Ascension/elevation (in reference frame )derivatives are computed with respect to spacecraft state in inertial frame
  146.         // and station parameters
  147.         // ----------------------
  148.         //
  149.         // Parameters:
  150.         //  - 0..2 - Position of the spacecraft in inertial frame
  151.         //  - 3..5 - Velocity of the spacecraft in inertial frame
  152.         //  - 6..n - station parameters (clock offset, station offsets, pole, prime meridian...)

  154.         // Get the number of parameters used for derivation
  155.         // Place the selected drivers into a map
  156.         int nbParams = 6;
  157.         final Map<String, Integer> indices = new HashMap<>();
  158.         for (ParameterDriver driver : getParametersDrivers()) {
  159.             if (driver.isSelected()) {
  160.                 indices.put(driver.getName(), nbParams++);
  161.             }
  162.         }
  163.         final DSFactory                          factory = new DSFactory(nbParams, 1);
  164.         final Field<DerivativeStructure>         field   = factory.getDerivativeField();
  165.         final FieldVector3D<DerivativeStructure> zero    = FieldVector3D.getZero(field);

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

  170.         // Transform between station and inertial frame, expressed as a derivative structure
  171.         // The components of station's position in offset frame are the 3 last derivative parameters
  172.         final FieldTransform<DerivativeStructure> offsetToInertialDownlink =
  173.                         station.getOffsetToInertial(state.getFrame(), getDate(), factory, indices);
  174.         final FieldAbsoluteDate<DerivativeStructure> downlinkDateDS =
  175.                         offsetToInertialDownlink.getFieldDate();

  177.         // Station position/velocity in inertial frame at end of the downlink leg
  178.         final TimeStampedFieldPVCoordinates<DerivativeStructure> stationDownlink =
  179.                         offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
  180.                                                                                                             zero, zero, zero));

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

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

  189.         // Transit state
  190.         final DerivativeStructure   delta        = downlinkDateDS.durationFrom(state.getDate());
  191.         final DerivativeStructure   deltaMTauD   = tauD.negate().add(delta);
  192.         final SpacecraftState       transitState = state.shiftedBy(deltaMTauD.getValue());

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

  197.         // Station-satellite vector expressed in inertial frame
  198.         final FieldVector3D<DerivativeStructure> staSatInertial = transitStateDS.getPosition().subtract(stationDownlink.getPosition());

  200.         // Field transform from inertial to reference frame at station's reception date
  201.         final FieldTransform<DerivativeStructure> inertialToReferenceDownlink =
  202.                         state.getFrame().getTransformTo(referenceFrame, downlinkDateDS);

  204.         // Station-satellite vector in reference frame
  205.         final FieldVector3D<DerivativeStructure> staSatReference = inertialToReferenceDownlink.transformPosition(staSatInertial);

  207.         // Compute right ascension and declination
  208.         final DerivativeStructure baseRightAscension = staSatReference.getAlpha();
  209.         final double              twoPiWrap          = MathUtils.normalizeAngle(baseRightAscension.getReal(),
  210.                                                                                 getObservedValue()[0]) - baseRightAscension.getReal();
  211.         final DerivativeStructure rightAscension     = baseRightAscension.add(twoPiWrap);
  212.         final DerivativeStructure declination        = staSatReference.getDelta();

  214.         // Prepare the estimation
  215.         final EstimatedMeasurement<AngularRaDec> estimated =
  216.                         new EstimatedMeasurement<>(this, iteration, evaluation,
  217.                                                    new SpacecraftState[] {
  218.                                                        transitState
  219.                                                    }, new TimeStampedPVCoordinates[] {
  220.                                                        transitStateDS.toTimeStampedPVCoordinates(),
  221.                                                        stationDownlink.toTimeStampedPVCoordinates()
  222.                                                    });

  224.         // azimuth - elevation values
  225.         estimated.setEstimatedValue(rightAscension.getValue(), declination.getValue());

  227.         // Partial derivatives of right ascension/declination in reference frame with respect to state
  228.         // (beware element at index 0 is the value, not a derivative)
  229.         final double[] raDerivatives  = rightAscension.getAllDerivatives();
  230.         final double[] decDerivatives = declination.getAllDerivatives();
  231.         estimated.setStateDerivatives(0,
  232.                                       Arrays.copyOfRange(raDerivatives, 1, 7), Arrays.copyOfRange(decDerivatives, 1, 7));

  234.         // Partial derivatives with respect to parameters
  235.         // (beware element at index 0 is the value, not a derivative)
  236.         for (final ParameterDriver driver : getParametersDrivers()) {
  237.             final Integer index = indices.get(driver.getName());
  238.             if (index != null) {
  239.                 estimated.setParameterDerivatives(driver, raDerivatives[index + 1], decDerivatives[index + 1]);
  240.             }
  241.         }

  243.         return estimated;
  244.     }
  245. }
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