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    * 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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  package org.orekit.estimation.sequential;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Comparator;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import org.hipparchus.filtering.kalman.ProcessEstimate;
  import org.hipparchus.linear.ArrayRealVector;
  import org.hipparchus.linear.MatrixUtils;
  import org.hipparchus.linear.RealMatrix;
  import org.hipparchus.linear.RealVector;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.estimation.measurements.EstimatedMeasurement;
  import org.orekit.propagation.Propagator;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.conversion.PropagatorBuilder;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.ParameterDriversList;
  import org.orekit.utils.ParameterDriversList.DelegatingDriver;
  
  /** Class defining the process model dynamics to use with a {@link KalmanEstimator}.
   * @author Romain Gerbaud
   * @author Maxime Journot
   * @since 9.2
   */
  abstract class AbstractKalmanEstimationCommon implements KalmanEstimation {
  
      /** Builders for propagators. */
      private final List<PropagatorBuilder> builders;
  
      /** Estimated orbital parameters. */
      private final ParameterDriversList allEstimatedOrbitalParameters;
  
      /** Estimated propagation drivers. */
      private final ParameterDriversList allEstimatedPropagationParameters;
  
      /** Per-builder estimated orbita parameters drivers.
       * @since 11.1
       */
      private final ParameterDriversList[] estimatedOrbitalParameters;
  
      /** Per-builder estimated propagation drivers. */
      private final ParameterDriversList[] estimatedPropagationParameters;
  
      /** Estimated measurements parameters. */
      private final ParameterDriversList estimatedMeasurementsParameters;
  
      /** Start columns for each estimated orbit. */
      private final int[] orbitsStartColumns;
  
      /** End columns for each estimated orbit. */
      private final int[] orbitsEndColumns;
  
      /** Map for propagation parameters columns. */
      private final Map<String, Integer> propagationParameterColumns;
  
      /** Map for measurements parameters columns. */
      private final Map<String, Integer> measurementParameterColumns;
  
      /** Providers for covariance matrices. */
      private final List<CovarianceMatrixProvider> covarianceMatricesProviders;
  
      /** Process noise matrix provider for measurement parameters. */
      private final CovarianceMatrixProvider measurementProcessNoiseMatrix;
  
      /** Indirection arrays to extract the noise components for estimated parameters. */
      private final int[][] covarianceIndirection;
  
      /** Scaling factors. */
      private final double[] scale;
  
      /** Current corrected estimate. */
      private ProcessEstimate correctedEstimate;
  
      /** Current number of measurement. */
      private int currentMeasurementNumber;
  
      /** Reference date. */
     private final AbsoluteDate referenceDate;
 
     /** Current date. */
     private AbsoluteDate currentDate;
 
     /** Predicted spacecraft states. */
     private final SpacecraftState[] predictedSpacecraftStates;
 
     /** Corrected spacecraft states. */
     private final SpacecraftState[] correctedSpacecraftStates;
 
     /** Predicted measurement. */
     private EstimatedMeasurement<?> predictedMeasurement;
 
     /** Corrected measurement. */
     private EstimatedMeasurement<?> correctedMeasurement;
 
     /** Kalman process model constructor.
      * @param propagatorBuilders propagators builders used to evaluate the orbits.
      * @param covarianceMatricesProviders providers for covariance matrices
      * @param estimatedMeasurementParameters measurement parameters to estimate
      * @param measurementProcessNoiseMatrix provider for measurement process noise matrix
      */
     protected AbstractKalmanEstimationCommon(final List<PropagatorBuilder> propagatorBuilders,
                                              final List<CovarianceMatrixProvider> covarianceMatricesProviders,
                                              final ParameterDriversList estimatedMeasurementParameters,
                                              final CovarianceMatrixProvider measurementProcessNoiseMatrix) {
 
         this.builders                        = propagatorBuilders;
         this.estimatedMeasurementsParameters = estimatedMeasurementParameters;
         this.measurementParameterColumns     = new HashMap<>(estimatedMeasurementsParameters.getDrivers().size());
         this.currentMeasurementNumber        = 0;
         this.referenceDate                   = propagatorBuilders.getFirst().getOrbitalParameterFactory().getDate();
         this.currentDate                     = referenceDate;
 
         final Map<String, Integer> orbitalParameterColumns = new HashMap<>(6 * builders.size());
         orbitsStartColumns      = new int[builders.size()];
         orbitsEndColumns        = new int[builders.size()];
         int columns = 0;
         allEstimatedOrbitalParameters = new ParameterDriversList();
         estimatedOrbitalParameters    = new ParameterDriversList[builders.size()];
         for (int k = 0; k < builders.size(); ++k) {
             estimatedOrbitalParameters[k] = new ParameterDriversList();
             orbitsStartColumns[k] = columns;
             final String suffix = propagatorBuilders.size() > 1 ? "[" + k + "]" : null;
             final ParameterDriversList drivers = builders.get(k).
                                                  getOrbitalParameterFactory().
                                                  getOrbitalParametersDrivers();
             for (final ParameterDriver driver : drivers.getDrivers()) {
                 if (driver.getReferenceDate() == null) {
                     driver.setReferenceDate(currentDate);
                 }
                 if (suffix != null && !driver.getName().endsWith(suffix)) {
                     // we add suffix only conditionally because the method may already have been called
                     // and suffixes may have already been appended
                     driver.setName(driver.getName() + suffix);
                 }
                 if (driver.isSelected()) {
                     allEstimatedOrbitalParameters.add(driver);
                     estimatedOrbitalParameters[k].add(driver);
                     orbitalParameterColumns.put(driver.getName(), columns++);
                 }
             }
             orbitsEndColumns[k] = columns;
         }
 
         // Gather all the propagation drivers names in a list
         allEstimatedPropagationParameters = new ParameterDriversList();
         estimatedPropagationParameters    = new ParameterDriversList[builders.size()];
         final List<String> estimatedPropagationParametersNames = new ArrayList<>();
         for (int k = 0; k < builders.size(); ++k) {
             estimatedPropagationParameters[k] = new ParameterDriversList();
             for (final ParameterDriver driver : builders.get(k).getPropagationParametersDrivers().getDrivers()) {
                 if (driver.getReferenceDate() == null) {
                     driver.setReferenceDate(currentDate);
                 }
                 if (driver.isSelected()) {
                     allEstimatedPropagationParameters.add(driver);
                     estimatedPropagationParameters[k].add(driver);
                     final String driverName = driver.getName();
                     // Add the driver name if it has not been added yet
                     if (!estimatedPropagationParametersNames.contains(driverName)) {
                         estimatedPropagationParametersNames.add(driverName);
                     }
                 }
             }
         }
         estimatedPropagationParametersNames.sort(Comparator.naturalOrder());
 
         // Populate the map of propagation drivers' columns and update the total number of columns
         propagationParameterColumns = new HashMap<>(estimatedPropagationParametersNames.size());
         for (final String driverName : estimatedPropagationParametersNames) {
             propagationParameterColumns.put(driverName, columns);
             ++columns;
         }
 
         // Populate the map of measurement drivers' columns and update the total number of columns
         for (final ParameterDriver parameter : estimatedMeasurementsParameters.getDrivers()) {
             if (parameter.getReferenceDate() == null) {
                 parameter.setReferenceDate(currentDate);
             }
             measurementParameterColumns.put(parameter.getName(), columns);
             ++columns;
         }
 
         // Store providers for process noise matrices
         this.covarianceMatricesProviders = covarianceMatricesProviders;
         this.measurementProcessNoiseMatrix = measurementProcessNoiseMatrix;
         this.covarianceIndirection       = new int[builders.size()][columns];
         for (int k = 0; k < covarianceIndirection.length; ++k) {
             final ParameterDriversList orbitDrivers      = builders.get(k).
                                                            getOrbitalParameterFactory().
                                                            getOrbitalParametersDrivers();
             final ParameterDriversList parametersDrivers = builders.get(k).
                                                            getPropagationParametersDrivers();
             Arrays.fill(covarianceIndirection[k], -1);
             int i = 0;
             for (final ParameterDriver driver : orbitDrivers.getDrivers()) {
                 final Integer c = orbitalParameterColumns.get(driver.getName());
                 if (c != null) {
                     covarianceIndirection[k][i++] = c;
                 }
             }
             for (final ParameterDriver driver : parametersDrivers.getDrivers()) {
                 final Integer c = propagationParameterColumns.get(driver.getName());
                 if (c != null) {
                     covarianceIndirection[k][i++] = c;
                 }
             }
             for (final ParameterDriver driver : estimatedMeasurementParameters.getDrivers()) {
                 final Integer c = measurementParameterColumns.get(driver.getName());
                 if (c != null) {
                     covarianceIndirection[k][i++] = c;
                 }
             }
         }
 
         // Compute the scale factors
         this.scale = new double[columns];
         int index = 0;
         for (final ParameterDriver driver : allEstimatedOrbitalParameters.getDrivers()) {
             scale[index++] = driver.getScale();
         }
         for (final ParameterDriver driver : allEstimatedPropagationParameters.getDrivers()) {
             scale[index++] = driver.getScale();
         }
         for (final ParameterDriver driver : estimatedMeasurementsParameters.getDrivers()) {
             scale[index++] = driver.getScale();
         }
 
         // Populate predicted and corrected states
         this.predictedSpacecraftStates = new SpacecraftState[builders.size()];
         for (int i = 0; i < builders.size(); ++i) {
             predictedSpacecraftStates[i] = builders.get(i).buildPropagator().getInitialState();
         }
         this.correctedSpacecraftStates = predictedSpacecraftStates.clone();
 
         // Initialize the estimated normalized state and fill its values
         final RealVector correctedState      = MatrixUtils.createRealVector(columns);
 
         int p = 0;
         for (final ParameterDriver driver : allEstimatedOrbitalParameters.getDrivers()) {
             correctedState.setEntry(p++, driver.getNormalizedValue());
         }
         for (final ParameterDriver driver : allEstimatedPropagationParameters.getDrivers()) {
             correctedState.setEntry(p++, driver.getNormalizedValue());
         }
         for (final ParameterDriver driver : estimatedMeasurementsParameters.getDrivers()) {
             correctedState.setEntry(p++, driver.getNormalizedValue());
         }
 
         // Set up initial covariance
         final RealMatrix physicalProcessNoise = MatrixUtils.createRealMatrix(columns, columns);
         for (int k = 0; k < covarianceMatricesProviders.size(); ++k) {
 
             // Number of estimated measurement parameters
             final int nbMeas = estimatedMeasurementParameters.getNbParams();
 
             // Number of estimated dynamic parameters (orbital + propagation)
             final int nbDyn  = orbitsEndColumns[k] - orbitsStartColumns[k] +
                     estimatedPropagationParameters[k].getNbParams();
 
             // Covariance matrix
             final RealMatrix noiseK = MatrixUtils.createRealMatrix(nbDyn + nbMeas, nbDyn + nbMeas);
             if (nbDyn > 0) {
                 final RealMatrix noiseP = covarianceMatricesProviders.get(k).
                         getInitialCovarianceMatrix(correctedSpacecraftStates[k]);
                 if (measurementProcessNoiseMatrix == null && noiseP.getRowDimension() != nbDyn + nbMeas) {
                     throw new OrekitException(OrekitMessages.WRONG_PROCESS_COVARIANCE_DIMENSION,
                             nbDyn + nbMeas, noiseP.getRowDimension());
                 } else if (measurementProcessNoiseMatrix != null && noiseP.getRowDimension() != nbDyn) {
                     throw new OrekitException(OrekitMessages.WRONG_PROCESS_COVARIANCE_DIMENSION,
                             nbDyn, noiseP.getRowDimension());
                 }
                 noiseK.setSubMatrix(noiseP.getData(), 0, 0);
             }
             if (measurementProcessNoiseMatrix != null) {
                 final RealMatrix noiseM = measurementProcessNoiseMatrix.
                         getInitialCovarianceMatrix(correctedSpacecraftStates[k]);
                 if (noiseM.getRowDimension() != nbMeas) {
                     throw new OrekitException(OrekitMessages.WRONG_MEASUREMENT_COVARIANCE_DIMENSION,
                             nbMeas, noiseM.getRowDimension());
                 }
                 noiseK.setSubMatrix(noiseM.getData(), nbDyn, nbDyn);
             }
 
             KalmanEstimatorUtil.checkDimension(noiseK.getRowDimension(),
                                                builders.get(k).getOrbitalParameterFactory().getOrbitalParametersDrivers(),
                                                builders.get(k).getPropagationParametersDrivers(),
                                                estimatedMeasurementsParameters);
 
             final int[] indK = covarianceIndirection[k];
             for (int i = 0; i < indK.length; ++i) {
                 if (indK[i] >= 0) {
                     for (int j = 0; j < indK.length; ++j) {
                         if (indK[j] >= 0) {
                             physicalProcessNoise.setEntry(indK[i], indK[j], noiseK.getEntry(i, j));
                         }
                     }
                 }
             }
 
         }
         final RealMatrix correctedCovariance = KalmanEstimatorUtil.normalizeCovarianceMatrix(physicalProcessNoise, scale);
 
         correctedEstimate = new ProcessEstimate(0.0, correctedState, correctedCovariance);
     }
 
 
     /** {@inheritDoc} */
     @Override
     public RealMatrix getPhysicalStateTransitionMatrix() {
         //  Un-normalize the state transition matrix (φ) from Hipparchus and return it.
         // φ is an mxm matrix where m = nbOrb + nbPropag + nbMeas
         // For each element [i,j] of normalized φ (φn), the corresponding physical value is:
         // φ[i,j] = φn[i,j] * scale[i] / scale[j]
         return correctedEstimate.getStateTransitionMatrix() == null ?
                 null : KalmanEstimatorUtil.unnormalizeStateTransitionMatrix(correctedEstimate.getStateTransitionMatrix(), scale);
     }
 
     /** {@inheritDoc} */
     @Override
     public RealMatrix getPhysicalMeasurementJacobian() {
         // Un-normalize the measurement matrix (H) from Hipparchus and return it.
         // H is an nxm matrix where:
         //  - m = nbOrb + nbPropag + nbMeas is the number of estimated parameters
         //  - n is the size of the measurement being processed by the filter
         // For each element [i,j] of normalized H (Hn) the corresponding physical value is:
         // H[i,j] = Hn[i,j] * σ[i] / scale[j]
         return correctedEstimate.getMeasurementJacobian() == null ?
                 null : KalmanEstimatorUtil.unnormalizeMeasurementJacobian(correctedEstimate.getMeasurementJacobian(),
                 scale,
                 correctedMeasurement.getObservedMeasurement().getTheoreticalStandardDeviation());
     }
 
     /** {@inheritDoc} */
     @Override
     public RealMatrix getPhysicalInnovationCovarianceMatrix() {
         // Un-normalize the innovation covariance matrix (S) from Hipparchus and return it.
         // S is an nxn matrix where n is the size of the measurement being processed by the filter
         // For each element [i,j] of normalized S (Sn) the corresponding physical value is:
         // S[i,j] = Sn[i,j] * σ[i] * σ[j]
         return correctedEstimate.getInnovationCovariance() == null ?
                 null : KalmanEstimatorUtil.unnormalizeInnovationCovarianceMatrix(correctedEstimate.getInnovationCovariance(),
                 predictedMeasurement.getObservedMeasurement().getTheoreticalStandardDeviation());
     }
 
     /** {@inheritDoc} */
     @Override
     public RealMatrix getPhysicalKalmanGain() {
         // Un-normalize the Kalman gain (K) from Hipparchus and return it.
         // K is an mxn matrix where:
         //  - m = nbOrb + nbPropag + nbMeas is the number of estimated parameters
         //  - n is the size of the measurement being processed by the filter
         // For each element [i,j] of normalized K (Kn) the corresponding physical value is:
         // K[i,j] = Kn[i,j] * scale[i] / σ[j]
         return correctedEstimate.getKalmanGain() == null ?
                 null : KalmanEstimatorUtil.unnormalizeKalmanGainMatrix(correctedEstimate.getKalmanGain(),
                 scale,
                 correctedMeasurement.getObservedMeasurement().getTheoreticalStandardDeviation());
     }
 
     /** {@inheritDoc} */
     @Override
     public SpacecraftState[] getPredictedSpacecraftStates() {
         return predictedSpacecraftStates.clone();
     }
 
     /** {@inheritDoc} */
     @Override
     public SpacecraftState[] getCorrectedSpacecraftStates() {
         return correctedSpacecraftStates.clone();
     }
 
     /** {@inheritDoc} */
     @Override
     public int getCurrentMeasurementNumber() {
         return currentMeasurementNumber;
     }
 
     /** {@inheritDoc} */
     @Override
     public AbsoluteDate getCurrentDate() {
         return currentDate;
     }
 
     /** {@inheritDoc} */
     @Override
     public EstimatedMeasurement<?> getPredictedMeasurement() {
         return predictedMeasurement;
     }
 
     /** {@inheritDoc} */
     @Override
     public EstimatedMeasurement<?> getCorrectedMeasurement() {
         return correctedMeasurement;
     }
 
     /** {@inheritDoc} */
     @Override
     public RealVector getPhysicalEstimatedState() {
         // Method {@link ParameterDriver#getValue()} is used to get
         // the physical values of the state.
         // The scales'array is used to get the size of the state vector
         final RealVector physicalEstimatedState = new ArrayRealVector(scale.length);
         int i = 0;
         for (final DelegatingDriver driver : getEstimatedOrbitalParameters().getDrivers()) {
             physicalEstimatedState.setEntry(i++, driver.getValue());
         }
         for (final DelegatingDriver driver : getEstimatedPropagationParameters().getDrivers()) {
             physicalEstimatedState.setEntry(i++, driver.getValue());
         }
         for (final DelegatingDriver driver : getEstimatedMeasurementsParameters().getDrivers()) {
             physicalEstimatedState.setEntry(i++, driver.getValue());
         }
 
         return physicalEstimatedState;
     }
 
     /** {@inheritDoc} */
     @Override
     public RealMatrix getPhysicalEstimatedCovarianceMatrix() {
         // Un-normalize the estimated covariance matrix (P) from Hipparchus and return it.
         // The covariance P is an mxm matrix where m = nbOrb + nbPropag + nbMeas
         // For each element [i,j] of P the corresponding normalized value is:
         // Pn[i,j] = P[i,j] / (scale[i]*scale[j])
         // Consequently: P[i,j] = Pn[i,j] * scale[i] * scale[j]
         return KalmanEstimatorUtil.unnormalizeCovarianceMatrix(correctedEstimate.getCovariance(), scale);
     }
 
     /** {@inheritDoc} */
     @Override
     public ParameterDriversList getEstimatedOrbitalParameters() {
         return allEstimatedOrbitalParameters;
     }
 
     /** {@inheritDoc} */
     @Override
     public ParameterDriversList getEstimatedPropagationParameters() {
         return allEstimatedPropagationParameters;
     }
 
     /** {@inheritDoc} */
     @Override
     public ParameterDriversList getEstimatedMeasurementsParameters() {
         return estimatedMeasurementsParameters;
     }
 
     /** Get the current corrected estimate.
      * @return current corrected estimate
      */
     public ProcessEstimate getEstimate() {
         return correctedEstimate;
     }
 
     /** Getter for the propagators.
      * @return the propagators
      */
     public List<PropagatorBuilder> getBuilders() {
         return builders;
     }
 
     /** Get the propagators estimated with the values set in the propagators builders.
      * @return propagators based on the current values in the builder
      */
     public Propagator[] getEstimatedPropagators() {
         // Return propagators built with current instantiation of the propagator builders
         final Propagator[] propagators = new Propagator[getBuilders().size()];
         for (int k = 0; k < getBuilders().size(); ++k) {
             propagators[k] = getBuilders().get(k).buildPropagator();
         }
         return propagators;
     }
 
     /** Get the normalized process noise matrix.
      *
      * @param stateDimension state dimension
      * @return the normalized process noise matrix
      */
     protected RealMatrix getNormalizedProcessNoise(final int stateDimension) {
         final RealMatrix physicalProcessNoise = MatrixUtils.createRealMatrix(stateDimension, stateDimension);
         for (int k = 0; k < covarianceMatricesProviders.size(); ++k) {
 
             // Number of estimated measurement parameters
             final int nbMeas = estimatedMeasurementsParameters.getNbParams();
 
             // Number of estimated dynamic parameters (orbital + propagation)
             final int nbDyn  = orbitsEndColumns[k] - orbitsStartColumns[k] +
                     estimatedPropagationParameters[k].getNbParams();
 
             // Covariance matrix
             final RealMatrix noiseK = MatrixUtils.createRealMatrix(nbDyn + nbMeas, nbDyn + nbMeas);
             if (nbDyn > 0) {
                 final RealMatrix noiseP = covarianceMatricesProviders.get(k).
                         getProcessNoiseMatrix(correctedSpacecraftStates[k],
                                 predictedSpacecraftStates[k]);
                 if (measurementProcessNoiseMatrix == null && noiseP.getRowDimension() != nbDyn + nbMeas) {
                     throw new OrekitException(OrekitMessages.WRONG_PROCESS_COVARIANCE_DIMENSION,
                             nbDyn + nbMeas, noiseP.getRowDimension());
                 } else if (measurementProcessNoiseMatrix != null && noiseP.getRowDimension() != nbDyn) {
                     throw new OrekitException(OrekitMessages.WRONG_PROCESS_COVARIANCE_DIMENSION,
                             nbDyn, noiseP.getRowDimension());
                 }
                 noiseK.setSubMatrix(noiseP.getData(), 0, 0);
             }
             if (measurementProcessNoiseMatrix != null) {
                 final RealMatrix noiseM = measurementProcessNoiseMatrix.
                         getProcessNoiseMatrix(correctedSpacecraftStates[k],
                                 predictedSpacecraftStates[k]);
                 if (noiseM.getRowDimension() != nbMeas) {
                     throw new OrekitException(OrekitMessages.WRONG_MEASUREMENT_COVARIANCE_DIMENSION,
                             nbMeas, noiseM.getRowDimension());
                 }
                 noiseK.setSubMatrix(noiseM.getData(), nbDyn, nbDyn);
             }
 
             KalmanEstimatorUtil.checkDimension(noiseK.getRowDimension(),
                                               builders.get(k).getOrbitalParameterFactory().getOrbitalParametersDrivers(),
                                               builders.get(k).getPropagationParametersDrivers(),
                                               estimatedMeasurementsParameters);
 
             final int[] indK = covarianceIndirection[k];
             for (int i = 0; i < indK.length; ++i) {
                 if (indK[i] >= 0) {
                     for (int j = 0; j < indK.length; ++j) {
                         if (indK[j] >= 0) {
                             physicalProcessNoise.setEntry(indK[i], indK[j], noiseK.getEntry(i, j));
                         }
                     }
                 }
             }
 
         }
         return KalmanEstimatorUtil.normalizeCovarianceMatrix(physicalProcessNoise, scale);
     }
 
     /** Getter for the orbitsStartColumns.
      * @return the orbitsStartColumns
      */
     protected int[] getOrbitsStartColumns() {
         return orbitsStartColumns;
     }
 
     /** Getter for the propagationParameterColumns.
      * @return the propagationParameterColumns
      */
     protected Map<String, Integer> getPropagationParameterColumns() {
         return propagationParameterColumns;
     }
 
     /** Getter for the measurementParameterColumns.
      * @return the measurementParameterColumns
      */
     protected Map<String, Integer> getMeasurementParameterColumns() {
         return measurementParameterColumns;
     }
 
     /** Getter for the estimatedPropagationParameters.
      * @return the estimatedPropagationParameters
      */
     protected ParameterDriversList[] getEstimatedPropagationParametersArray() {
         return estimatedPropagationParameters;
     }
 
     /** Getter for the estimatedOrbitalParameters.
      * @return the estimatedOrbitalParameters
      */
     protected ParameterDriversList[] getEstimatedOrbitalParametersArray() {
         return estimatedOrbitalParameters;
     }
 
     /** Getter for the covarianceIndirection.
      * @return the covarianceIndirection
      */
     protected int[][] getCovarianceIndirection() {
         return covarianceIndirection;
     }
 
     /** Getter for the scale.
      * @return the scale
      */
     protected double[] getScale() {
         return scale;
     }
 
     /** Getter for the correctedEstimate.
      * @return the correctedEstimate
      */
     protected ProcessEstimate getCorrectedEstimate() {
         return correctedEstimate;
     }
 
     /** Setter for the correctedEstimate.
      * @param correctedEstimate the correctedEstimate
      */
     protected void setCorrectedEstimate(final ProcessEstimate correctedEstimate) {
         this.correctedEstimate = correctedEstimate;
     }
 
     /** Getter for the referenceDate.
      * @return the referenceDate
      */
     protected AbsoluteDate getReferenceDate() {
         return referenceDate;
     }
 
     /** Increment current measurement number. */
     protected void incrementCurrentMeasurementNumber() {
         currentMeasurementNumber += 1;
     }
 
     /** Setter for the currentDate.
      * @param currentDate the currentDate
      */
     protected void setCurrentDate(final AbsoluteDate currentDate) {
         this.currentDate = currentDate;
     }
 
     /** Set correctedSpacecraftState at index.
      *
      * @param correctedSpacecraftState corrected S/C state o set
      * @param index index where to set in the array
      */
     protected void setCorrectedSpacecraftState(final SpacecraftState correctedSpacecraftState, final int index) {
         this.correctedSpacecraftStates[index] = correctedSpacecraftState;
     }
 
     /** Set predictedSpacecraftState at index.
      *
      * @param predictedSpacecraftState predicted S/C state o set
      * @param index index where to set in the array
      */
     protected void setPredictedSpacecraftState(final SpacecraftState predictedSpacecraftState, final int index) {
         this.predictedSpacecraftStates[index] = predictedSpacecraftState;
     }
 
     /** Setter for the predictedMeasurement.
      * @param predictedMeasurement the predictedMeasurement
      */
     protected void setPredictedMeasurement(final EstimatedMeasurement<?> predictedMeasurement) {
         this.predictedMeasurement = predictedMeasurement;
     }
 
     /** Setter for the correctedMeasurement.
      * @param correctedMeasurement the correctedMeasurement
      */
     protected void setCorrectedMeasurement(final EstimatedMeasurement<?> correctedMeasurement) {
         this.correctedMeasurement = correctedMeasurement;
     }
 }