AngularRaDec.java

  1. /* Copyright 2002-2025 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;

  19. import java.util.Arrays;

  21. import org.hipparchus.analysis.differentiation.Gradient;
  22. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  23. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  24. import org.hipparchus.util.MathUtils;
  25. import org.orekit.frames.FieldStaticTransform;
  26. import org.orekit.frames.Frame;
  27. import org.orekit.frames.StaticTransform;
  28. import org.orekit.propagation.SpacecraftState;
  29. import org.orekit.time.AbsoluteDate;
  30. import org.orekit.utils.ParameterDriver;
  31. import org.orekit.utils.TimeSpanMap.Span;
  32. import org.orekit.utils.TimeStampedFieldPVCoordinates;
  33. import org.orekit.utils.TimeStampedPVCoordinates;

  35. /** Class modeling a Right Ascension - Declination measurement from a ground point (station, telescope).
  36.  * The angles are given in an inertial reference frame.
  37.  * The motion of the spacecraft during the signal flight time is taken into
  38.  * account. The date of the measurement corresponds to the reception on
  39.  * ground of the reflected signal.
  40.  *
  41.  * @author Thierry Ceolin
  42.  * @author Maxime Journot
  43.  * @since 9.0
  44.  */
  45. public class AngularRaDec extends GroundReceiverMeasurement<AngularRaDec> {

  47.     /** Type of the measurement. */
  48.     public static final String MEASUREMENT_TYPE = "AngularRaDec";

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

  53.     /** Simple constructor.
  54.      * @param station ground station from which measurement is performed
  55.      * @param referenceFrame Reference frame in which the right ascension - declination angles are given
  56.      * @param date date of the measurement
  57.      * @param angular observed value
  58.      * @param sigma theoretical standard deviation
  59.      * @param baseWeight base weight
  60.      * @param satellite satellite related to this measurement
  61.      * @since 9.3
  62.      */
  63.     public AngularRaDec(final GroundStation station, final Frame referenceFrame, final AbsoluteDate date,
  64.                         final double[] angular, final double[] sigma, final double[] baseWeight,
  65.                         final ObservableSatellite satellite) {
  66.         super(station, false, date, angular, sigma, baseWeight, satellite);
  67.         this.referenceFrame = referenceFrame;
  68.     }

  70.     /** Get the reference frame in which the right ascension - declination angles are given.
  71.      * @return reference frame in which the right ascension - declination angles are given
  72.      */
  73.     public Frame getReferenceFrame() {
  74.         return referenceFrame;
  75.     }

  77.     /** {@inheritDoc} */
  78.     @Override
  79.     protected EstimatedMeasurementBase<AngularRaDec> theoreticalEvaluationWithoutDerivatives(final int iteration,
  80.                                                                                              final int evaluation,
  81.                                                                                              final SpacecraftState[] states) {

  83.         final GroundReceiverCommonParametersWithoutDerivatives common = computeCommonParametersWithout(states[0]);
  84.         final TimeStampedPVCoordinates transitPV = common.getTransitPV();

  86.         // Station-satellite vector expressed in inertial frame
  87.         final Vector3D staSatInertial = transitPV.getPosition().subtract(common.getStationDownlink().getPosition());

  89.         // Field transform from inertial to reference frame at station's reception date
  90.         final StaticTransform inertialToReferenceDownlink = common.getState().getFrame().
  91.                                                             getStaticTransformTo(referenceFrame, common.getStationDownlink().getDate());

  93.         // Station-satellite vector in reference frame
  94.         final Vector3D staSatReference = inertialToReferenceDownlink.transformVector(staSatInertial);

  96.         // Compute right ascension and declination
  97.         final double baseRightAscension = staSatReference.getAlpha();
  98.         final double twoPiWrap          = MathUtils.normalizeAngle(baseRightAscension, getObservedValue()[0]) - baseRightAscension;
  99.         final double rightAscension     = baseRightAscension + twoPiWrap;
  100.         final double declination        = staSatReference.getDelta();

  102.         // Prepare the estimation
  103.         final EstimatedMeasurementBase<AngularRaDec> estimated =
  104.                         new EstimatedMeasurementBase<>(this, iteration, evaluation,
  105.                                                        new SpacecraftState[] {
  106.                                                            common.getTransitState()
  107.                                                        }, new TimeStampedPVCoordinates[] {
  108.                                                            transitPV,
  109.                                                            common.getStationDownlink()
  110.                                                        });

  112.         // azimuth - elevation values
  113.         estimated.setEstimatedValue(rightAscension, declination);

  115.         return estimated;

  117.     }

  119.     /** {@inheritDoc} */
  120.     @Override
  121.     protected EstimatedMeasurement<AngularRaDec> theoreticalEvaluation(final int iteration, final int evaluation,
  122.                                                                        final SpacecraftState[] states) {

  124.         final SpacecraftState state = states[0];

  126.         // Right Ascension/elevation (in reference frame )derivatives are computed with respect to spacecraft state in inertial frame
  127.         // and station parameters
  128.         // ----------------------
  129.         //
  130.         // Parameters:
  131.         //  - 0..2 - Position of the spacecraft in inertial frame
  132.         //  - 3..5 - Velocity of the spacecraft in inertial frame
  133.         //  - 6..n - station parameters (clock offset, station offsets, pole, prime meridian...)
  134.         final GroundReceiverCommonParametersWithDerivatives common = computeCommonParametersWithDerivatives(state);
  135.         final TimeStampedFieldPVCoordinates<Gradient> transitPV = common.getTransitPV();

  137.         // Station-satellite vector expressed in inertial frame
  138.         final FieldVector3D<Gradient> staSatInertial = transitPV.getPosition().subtract(common.getStationDownlink().getPosition());

  140.         // Field transform from inertial to reference frame at station's reception date
  141.         final FieldStaticTransform<Gradient> inertialToReferenceDownlink =
  142.                         state.getFrame().getStaticTransformTo(referenceFrame, common.getStationDownlink().getDate());

  144.         // Station-satellite vector in reference frame
  145.         final FieldVector3D<Gradient> staSatReference = inertialToReferenceDownlink.transformVector(staSatInertial);

  147.         // Compute right ascension and declination
  148.         final Gradient baseRightAscension = staSatReference.getAlpha();
  149.         final double   twoPiWrap          = MathUtils.normalizeAngle(baseRightAscension.getReal(),
  150.                                                                                 getObservedValue()[0]) - baseRightAscension.getReal();
  151.         final Gradient rightAscension     = baseRightAscension.add(twoPiWrap);
  152.         final Gradient declination        = staSatReference.getDelta();

  154.         // Prepare the estimation
  155.         final EstimatedMeasurement<AngularRaDec> estimated =
  156.                         new EstimatedMeasurement<>(this, iteration, evaluation,
  157.                                                    new SpacecraftState[] {
  158.                                                        common.getTransitState()
  159.                                                    }, new TimeStampedPVCoordinates[] {
  160.                                                        transitPV.toTimeStampedPVCoordinates(),
  161.                                                        common.getStationDownlink().toTimeStampedPVCoordinates()
  162.                                                    });

  164.         // azimuth - elevation values
  165.         estimated.setEstimatedValue(rightAscension.getValue(), declination.getValue());

  167.         // Partial derivatives of right ascension/declination in reference frame with respect to state
  168.         final double[] raDerivatives  = rightAscension.getGradient();
  169.         final double[] decDerivatives = declination.getGradient();
  170.         estimated.setStateDerivatives(0,
  171.                                       Arrays.copyOfRange(raDerivatives, 0, 6), Arrays.copyOfRange(decDerivatives, 0, 6));

  173.         // Partial derivatives with respect to parameters
  174.         for (final ParameterDriver driver : getParametersDrivers()) {
  175.             for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
  176.                 final Integer index = common.getIndices().get(span.getData());
  177.                 if (index != null) {
  178.                     estimated.setParameterDerivatives(driver, span.getStart(), raDerivatives[index], decDerivatives[index]);
  179.                 }
  180.             }
  181.         }

  183.         return estimated;

  185.     }

  187.     /** Calculate the Line Of Sight of the given measurement.
  188.      * @param outputFrame output frame of the line of sight vector
  189.      * @return Vector3D the line of Sight of the measurement
  190.      * @since 12.0
  191.      */
  192.     public Vector3D getObservedLineOfSight(final Frame outputFrame) {
  193.         return referenceFrame.getStaticTransformTo(outputFrame, getDate())
  194.             .transformVector(new Vector3D(getObservedValue()[0], getObservedValue()[1]));
  195.     }
  196. }
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