/* 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
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  package org.orekit.estimation.measurements;
  
  import java.util.Arrays;
  
  import org.hipparchus.analysis.UnivariateFunction;
  import org.hipparchus.analysis.solvers.BracketingNthOrderBrentSolver;
  import org.hipparchus.analysis.solvers.UnivariateSolver;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.MathUtils;
  import org.orekit.estimation.Context;
  import org.orekit.frames.Frame;
  import org.orekit.frames.Transform;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.Constants;
  import org.orekit.utils.ParameterDriver;
  
  public class AngularRaDecMeasurementCreator extends MeasurementCreator {
  
      private final Context context;
      private final ObservableSatellite satellite;
  
      public AngularRaDecMeasurementCreator(final Context context) {
          this.context   = context;
          this.satellite = new ObservableSatellite(0);
      }
  
      public void init(SpacecraftState s0, AbsoluteDate t, double step) {
          for (final GroundStation station : context.stations) {
              for (ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
                                                          station.getEastOffsetDriver(),
                                                          station.getNorthOffsetDriver(),
                                                          station.getZenithOffsetDriver(),
                                                          station.getPrimeMeridianOffsetDriver(),
                                                          station.getPrimeMeridianDriftDriver(),
                                                          station.getPolarOffsetXDriver(),
                                                          station.getPolarDriftXDriver(),
                                                          station.getPolarOffsetYDriver(),
                                                          station.getPolarDriftYDriver())) {
                  if (driver.getReferenceDate() == null) {
                      driver.setReferenceDate(s0.getDate());
                  }
              }
  
          }
      }
  
      public void handleStep(final SpacecraftState currentState) {
          for (final GroundStation station : context.stations) {
  
              final AbsoluteDate     date      = currentState.getDate();
              final Frame            inertial  = currentState.getFrame();
              final Vector3D         position  = currentState.getPVCoordinates().getPosition();
  
              if (station.getBaseFrame().getElevation(position, inertial, date) > FastMath.toRadians(30.0)) {
                  final UnivariateSolver solver = new BracketingNthOrderBrentSolver(1.0e-12, 5);
  
                  final double downLinkDelay  = solver.solve(1000, new UnivariateFunction() {
                      public double value(final double x) {
                          final Transform t = station.getOffsetToInertial(inertial, date.shiftedBy(x));
                          final double d = Vector3D.distance(position, t.transformPosition(Vector3D.ZERO));
                          return d - x * Constants.SPEED_OF_LIGHT;
                      }
                  }, -1.0, 1.0);
  
                  // Satellite position at signal departure
                  final Vector3D satelliteAtDeparture = currentState.shiftedBy(-downLinkDelay).getPVCoordinates().getPosition();
  
                  // Initialize measurement
                  final double[] angular = new double[2];
                  final double[] sigma = {1.0, 1.0};
                  final double[] baseweight = {10.0, 10.0};
                  
                  // Inertial frame used
                  final Frame inertialFrame = context.initialOrbit.getFrame();
                  
                  // Station position at signal arrival
                  // Set the reference date of offset drivers arbitrarily to avoid exception
                  station.getPrimeMeridianOffsetDriver().setReferenceDate(date);
                  station.getPolarOffsetXDriver().setReferenceDate(date);
                  station.getPolarOffsetYDriver().setReferenceDate(date);
                  final Transform offsetToInertialArrival = station.getOffsetToInertial(inertialFrame, date);
                 final Vector3D  stationPArrival = offsetToInertialArrival.transformPosition(Vector3D.ZERO);
                 
                 // Vector station position at signal arrival - satellite at signal departure
                 // In inertial reference frame
                 final Vector3D staSat = satelliteAtDeparture.subtract(stationPArrival);
 
                 // Compute measurement
                 // Right ascension
                 final double baseRightAscension = staSat.getAlpha();
                 angular[0] = MathUtils.normalizeAngle(baseRightAscension, 0.0);
 
                 // Declination
                 angular[1] = staSat.getDelta();
 
                 addMeasurement(new AngularRaDec(station, inertialFrame, date, angular, sigma, baseweight, satellite));
             }
 
         }
     }
 
 }