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    *   http://www.apache.org/licenses/LICENSE-2.0
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   * Unless required by applicable law or agreed to in writing, software
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  package org.orekit.estimation.measurements.modifiers;
  
  import java.util.Arrays;
  
  import org.hipparchus.analysis.differentiation.Gradient;
  import org.orekit.estimation.measurements.EstimatedMeasurement;
  import org.orekit.estimation.measurements.EstimatedMeasurementBase;
  import org.orekit.estimation.measurements.EstimationModifier;
  import org.orekit.estimation.measurements.GroundStation;
  import org.orekit.estimation.measurements.ObservedMeasurement;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.integration.AbstractGradientConverter;
  import org.orekit.utils.Differentiation;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.ParameterDriversProvider;
  import org.orekit.utils.TimeSpanMap.Span;
  
  /** Utility class modifying theoretical range-rate measurement.
   * @author Joris Olympio
   * @since 11.2
   */
  public class RangeRateModifierUtil {
  
      /** Private constructor for utility class.*/
      private RangeRateModifierUtil() {
          // not used
      }
  
      /** Apply a modifier to an estimated measurement.
       * @param <T> type of the measurement
       * @param estimated estimated measurement to modify
       * @param station ground station
       * @param modelEffect model effect
       * @param modifier applied modifier
       * @since 12.1
       */
      public static <T extends ObservedMeasurement<T>> void modifyWithoutDerivatives(final EstimatedMeasurementBase<T> estimated,
                                                                                     final GroundStation station,
                                                                                     final ParametricModelEffect modelEffect,
                                                                                     final EstimationModifier<T> modifier) {
  
          final SpacecraftState state    = estimated.getStates()[0];
  
          // update estimated value taking into account the delay. The  delay is directly added to the range.
          final double[] newValue = estimated.getEstimatedValue();
          final double delay = modelEffect.evaluate(station, state);
          newValue[0] = newValue[0] + delay;
          estimated.modifyEstimatedValue(modifier, newValue);
  
      }
  
      /** Apply a modifier to an estimated measurement.
       * @param <T> type of the measurement
       * @param estimated estimated measurement to modify
       * @param station ground station
       * @param converter gradient converter
       * @param parametricModel parametric modifier model
       * @param modelEffect model effect
       * @param modelEffectGradient model effect gradient
       * @param modifier applied modifier
       * @since 12.1
       */
      public static <T extends ObservedMeasurement<T>> void modify(final EstimatedMeasurement<T> estimated,
                                                                   final ParameterDriversProvider parametricModel,
                                                                   final AbstractGradientConverter converter,
                                                                   final GroundStation station,
                                                                   final ParametricModelEffect modelEffect,
                                                                   final ParametricModelEffectGradient modelEffectGradient,
                                                                   final EstimationModifier<T> modifier) {
  
          final SpacecraftState state = estimated.getStates()[0];
  
          // update estimated derivatives with Jacobian of the measure wrt state
          final FieldSpacecraftState<Gradient> gState = converter.getState(parametricModel);
          final Gradient[] gParameters = converter.getParameters(gState, parametricModel);
          final Gradient gDelay = modelEffectGradient.evaluate(station, gState, gParameters);
          final double[] derivatives = gDelay.getGradient();
  
          // update estimated derivatives with Jacobian of the measure wrt state
          final double[][] stateDerivatives = estimated.getStateDerivatives(0);
          for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
              stateDerivatives[0][jcol] += derivatives[jcol];
         }
         estimated.setStateDerivatives(0, stateDerivatives);
 
         int index = 0;
         for (final ParameterDriver driver : parametricModel.getParametersDrivers()) {
             if (driver.isSelected()) {
                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
 
                     // update estimated derivatives with derivative of the modification wrt modifier parameters
                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
                     parameterDerivative += derivatives[index + converter.getFreeStateParameters()];
                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
                     index = index + 1;
                 }
             }
 
         }
 
         for (final ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
                                                           station.getEastOffsetDriver(),
                                                           station.getNorthOffsetDriver(),
                                                           station.getZenithOffsetDriver())) {
             if (driver.isSelected()) {
                 for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
 
                     // update estimated derivatives with derivative of the modification wrt station parameters
                     double parameterDerivative = estimated.getParameterDerivatives(driver, span.getStart())[0];
                     parameterDerivative += Differentiation.differentiate((d, t) -> modelEffect.evaluate(station, state),
                                                                          3, 10.0 * driver.getScale()).value(driver, state.getDate());
                     estimated.setParameterDerivatives(driver, span.getStart(), parameterDerivative);
                 }
             }
         }
 
         // update estimated value taking into account the delay.
         modifyWithoutDerivatives(estimated, station, modelEffect, modifier);
 
     }
 
 }