/* Copyright 2002-2021 CS GROUP
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
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   * See the License for the specific language governing permissions and
   * limitations under the License.
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  package org.orekit.estimation.measurements.modifiers;
  
  import java.util.Collections;
  import java.util.List;
  
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.orekit.attitudes.AttitudeProvider;
  import org.orekit.estimation.measurements.EstimatedMeasurement;
  import org.orekit.estimation.measurements.EstimationModifier;
  import org.orekit.estimation.measurements.gnss.OneWayGNSSRange;
  import org.orekit.frames.Transform;
  import org.orekit.orbits.CartesianOrbit;
  import org.orekit.orbits.Orbit;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.TimeStampedPVCoordinates;
  
  /** On-board antenna offset effect on one-way GNSS range measurements.
   * @author Bryan Cazabonne
   * @since 10.3
   */
  public class OnBoardAntennaOneWayGNSSRangeModifier implements EstimationModifier<OneWayGNSSRange> {
  
      /** Position of the Antenna Phase Center in satellite 1 frame. */
      private final Vector3D antennaPhaseCenter1;
  
      /** Position of the Antenna Phase Center in satellite 2 frame. */
      private final Vector3D antennaPhaseCenter2;
  
      /** Attitude provider of the emitting satellite. */
      private final AttitudeProvider attitude;
  
      /** Simple constructor.
       * @param antennaPhaseCenter1 position of the Antenna Phase Center in satellite 1 frame
       * (i.e. the satellite which receives the signal and performs the measurement)
       * @param antennaPhaseCenter2 position of the Antenna Phase Center in satellite 2 frame
       * (i.e. the satellite which simply emits the signal)
       * @param attitude attitude provider of the emitting satellite
       */
      public OnBoardAntennaOneWayGNSSRangeModifier(final Vector3D antennaPhaseCenter1,
                                                   final Vector3D antennaPhaseCenter2,
                                                   final AttitudeProvider attitude) {
          this.antennaPhaseCenter1 = antennaPhaseCenter1;
          this.antennaPhaseCenter2 = antennaPhaseCenter2;
          this.attitude            = attitude;
      }
  
      /** {@inheritDoc} */
      @Override
      public List<ParameterDriver> getParametersDrivers() {
          return Collections.emptyList();
      }
  
      /** {@inheritDoc} */
      @Override
      public void modify(final EstimatedMeasurement<OneWayGNSSRange> estimated) {
  
          // The participants are remote satellite at emission, local satellite at reception
          final TimeStampedPVCoordinates[] participants  = estimated.getParticipants();
          final AbsoluteDate               emissionDate  = participants[0].getDate();
          final AbsoluteDate               receptionDate = participants[1].getDate();
  
          // Transforms from spacecraft to inertial frame at reception date
          final SpacecraftState refStateLocal              = estimated.getStates()[0];
          final SpacecraftState receptionState             = refStateLocal.shiftedBy(receptionDate.durationFrom(refStateLocal.getDate()));
          final Transform       receptionSpacecraftToInert = receptionState.toTransform().getInverse();
  
          // Orbit of the remote satellite
          final Orbit orbitRemote = new CartesianOrbit(participants[0], refStateLocal.getFrame(), receptionState.getMu());
  
          // Transforms from spacecraft to inertial frame at emission date
          final SpacecraftState refStateRemote             = new SpacecraftState(orbitRemote,
                                                                                 attitude.getAttitude(orbitRemote,
                                                                                                      orbitRemote.getDate(),
                                                                                                      orbitRemote.getFrame()));
          final SpacecraftState emissionState              = refStateRemote.shiftedBy(emissionDate.durationFrom(refStateRemote.getDate()));
          final Transform       emissionSpacecraftToInert  = emissionState.toTransform().getInverse();
  
          // Compute the geometrical value of the one-way GNSS range directly from participants positions.
          // Note that this may be different from the value returned by estimated.getEstimatedValue(),
          // because other modifiers may already have been taken into account
          final Vector3D pSpacecraftReception = receptionSpacecraftToInert.transformPosition(Vector3D.ZERO);
         final Vector3D pSpacecraftEmission  = emissionSpacecraftToInert.transformPosition(Vector3D.ZERO);
         final double oneWayGNSSRangeUsingSpacecraftCenter = Vector3D.distance(pSpacecraftEmission, pSpacecraftReception);
 
         // Compute the geometrical value of the range replacing
         // the spacecraft positions with antenna phase center positions
         final Vector3D pAPCReception = receptionSpacecraftToInert.transformPosition(antennaPhaseCenter1);
         final Vector3D pAPCEmission  = emissionSpacecraftToInert.transformPosition(antennaPhaseCenter2);
         final double oneWayGNSSRangeUsingAntennaPhaseCenter = Vector3D.distance(pAPCEmission, pAPCReception);
 
         // Get the estimated value before this modifier is applied
         final double[] value = estimated.getEstimatedValue();
 
         // Modify the value
         value[0] += oneWayGNSSRangeUsingAntennaPhaseCenter - oneWayGNSSRangeUsingSpacecraftCenter;
         estimated.setEstimatedValue(value);
 
     }
 
 }