/*
    * Copyright (C) 2020 Alberto Irurueta Carro (alberto@irurueta.com)
    *
    * Licensed 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,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.irurueta.navigation.inertial.calibration.accelerometer;
  
  import com.irurueta.algebra.Matrix;
  import com.irurueta.algebra.WrongSizeException;
  import com.irurueta.navigation.LockedException;
  import com.irurueta.navigation.NotReadyException;
  import com.irurueta.navigation.inertial.BodyKinematics;
  import com.irurueta.navigation.inertial.INSLooselyCoupledKalmanInitializerConfig;
  import com.irurueta.navigation.inertial.INSTightlyCoupledKalmanInitializerConfig;
  import com.irurueta.navigation.inertial.calibration.AccelerationTriad;
  import com.irurueta.navigation.inertial.calibration.AccelerometerBiasUncertaintySource;
  import com.irurueta.navigation.inertial.calibration.AccelerometerCalibrationSource;
  import com.irurueta.navigation.inertial.calibration.CalibrationException;
  import com.irurueta.navigation.inertial.calibration.StandardDeviationFrameBodyKinematics;
  import com.irurueta.navigation.inertial.estimators.ECEFKinematicsEstimator;
  import com.irurueta.numerical.robust.InliersData;
  import com.irurueta.numerical.robust.RobustEstimatorMethod;
  import com.irurueta.units.Acceleration;
  import com.irurueta.units.AccelerationConverter;
  import com.irurueta.units.AccelerationUnit;
  
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * This is an abstract class to robustly estimate accelerometer
   * biases, cross couplings and scaling factors.
   * <p>
   * To use this calibrator at least 4 measurements at different known frames must
   * be provided. In other words, accelerometer samples must be obtained at 4
   * different positions, orientations and velocities (although typically velocities are
   * always zero).
   * <p>
   * Measured specific force is assumed to follow the model shown below:
   * <pre>
   *     fmeas = ba + (I + Ma) * ftrue + w
   * </pre>
   * Where:
   * - fmeas is the measured specific force. This is a 3x1 vector.
   * - ba is accelerometer bias. Ideally, on a perfect accelerometer, this should be a
   * 3x1 zero vector.
   * - I is the 3x3 identity matrix.
   * - Ma is the 3x3 matrix containing cross-couplings and scaling factors. Ideally, on
   * a perfect accelerometer, this should be a 3x3 zero matrix.
   * - ftrue is ground-truth specific force.
   * - w is measurement noise.
   */
  public abstract class RobustKnownFrameAccelerometerCalibrator implements
          AccelerometerNonLinearCalibrator, UnknownBiasNonLinearAccelerometerCalibrator, AccelerometerCalibrationSource,
          AccelerometerBiasUncertaintySource, OrderedStandardDeviationFrameBodyKinematicsAccelerometerCalibrator,
          QualityScoredAccelerometerCalibrator {
  
      /**
       * Indicates whether by default a common z-axis is assumed for both the accelerometer
       * and gyroscope.
       */
      public static final boolean DEFAULT_USE_COMMON_Z_AXIS = false;
  
      /**
       * Required minimum number of measurements.
       */
      public static final int MINIMUM_MEASUREMENTS = 4;
  
      /**
       * Indicates that by default a linear calibrator is used for preliminary solution estimation.
       * The result obtained on each preliminary solution might be later refined.
       */
      public static final boolean DEFAULT_USE_LINEAR_CALIBRATOR = true;
  
      /**
       * Indicates that by default preliminary solutions are refined.
       */
      public static final boolean DEFAULT_REFINE_PRELIMINARY_SOLUTIONS = false;
  
      /**
       * Default robust estimator method when none is provided.
       */
      public static final RobustEstimatorMethod DEFAULT_ROBUST_METHOD = RobustEstimatorMethod.LMEDS;
  
      /**
       * Indicates that result is refined by default using a non-linear calibrator
       * (which uses a Levenberg-Marquardt fitter).
       */
      public static final boolean DEFAULT_REFINE_RESULT = true;
 
     /**
      * Indicates that covariance is kept by default after refining result.
      */
     public static final boolean DEFAULT_KEEP_COVARIANCE = true;
 
     /**
      * Default amount of progress variation before notifying a change in estimation progress.
      * By default this is set to 5%.
      */
     public static final float DEFAULT_PROGRESS_DELTA = 0.05f;
 
     /**
      * Minimum allowed value for progress delta.
      */
     public static final float MIN_PROGRESS_DELTA = 0.0f;
 
     /**
      * Maximum allowed value for progress delta.
      */
     public static final float MAX_PROGRESS_DELTA = 1.0f;
 
     /**
      * Constant defining default confidence of the estimated result, which is
      * 99%. This means that with a probability of 99% estimation will be
      * accurate because chosen sub-samples will be inliers.
      */
     public static final double DEFAULT_CONFIDENCE = 0.99;
 
     /**
      * Default maximum allowed number of iterations.
      */
     public static final int DEFAULT_MAX_ITERATIONS = 5000;
 
     /**
      * Minimum allowed confidence value.
      */
     public static final double MIN_CONFIDENCE = 0.0;
 
     /**
      * Maximum allowed confidence value.
      */
     public static final double MAX_CONFIDENCE = 1.0;
 
     /**
      * Minimum allowed number of iterations.
      */
     public static final int MIN_ITERATIONS = 1;
 
     /**
      * Contains a list of body kinematics measurements taken at different
      * frames (positions, orientations and velocities) and containing the standard
      * deviations of accelerometer and gyroscope measurements.
      * If a single device IMU needs to be calibrated, typically all measurements are
      * taken at the same position, with zero velocity and multiple orientations.
      * However, if we just want to calibrate a given IMU model (e.g. obtain
      * an average and less precise calibration for the IMU of a given phone model),
      * we could take measurements collected throughout the planet at multiple positions
      * while the phone remains static (e.g. while charging), hence each measurement
      * position will change, velocity will remain zero and orientation will be
      * typically constant at horizontal orientation while the phone remains on a
      * flat surface.
      */
     protected List<StandardDeviationFrameBodyKinematics> measurements;
 
     /**
      * Listener to be notified of events such as when calibration starts, ends or its
      * progress significantly changes.
      */
     protected RobustKnownFrameAccelerometerCalibratorListener listener;
 
     /**
      * Indicates whether calibrator is running.
      */
     protected boolean running;
 
     /**
      * Amount of progress variation before notifying a progress change during calibration.
      */
     protected float progressDelta = DEFAULT_PROGRESS_DELTA;
 
     /**
      * Amount of confidence expressed as a value between 0.0 and 1.0 (which is equivalent
      * to 100%). The amount of confidence indicates the probability that the estimated
      * result is correct. Usually this value will be close to 1.0, but not exactly 1.0.
      */
     protected double confidence = DEFAULT_CONFIDENCE;
 
     /**
      * Maximum allowed number of iterations. When the maximum number of iterations is
      * exceeded, result will not be available, however an approximate result will be
      * available for retrieval.
      */
     protected int maxIterations = DEFAULT_MAX_ITERATIONS;
 
     /**
      * Data related to inliers found after calibration.
      */
     protected InliersData inliersData;
 
     /**
      * Indicates whether result must be refined using a non linear calibrator over
      * found inliers.
      * If true, inliers will be computed and kept in any implementation regardless of the
      * settings.
      */
     protected boolean refineResult = DEFAULT_REFINE_RESULT;
 
     /**
      * Size of subsets to be checked during robust estimation.
      */
     protected int preliminarySubsetSize = MINIMUM_MEASUREMENTS;
 
     /**
      * This flag indicates whether z-axis is assumed to be common for accelerometer
      * and gyroscope.
      * When enabled, this eliminates 3 variables from Ma matrix.
      */
     private boolean commonAxisUsed = DEFAULT_USE_COMMON_Z_AXIS;
 
     /**
      * Initial x-coordinate of accelerometer bias to be used to find a solution.
      * This is expressed in meters per squared second (m/s^2).
      */
     private double initialBiasX;
 
     /**
      * Initial y-coordinate of accelerometer bias to be used to find a solution.
      * This is expressed in meters per squared second (m/s^2).
      */
     private double initialBiasY;
 
     /**
      * Initial z-coordinate of accelerometer bias to be used to find a solution.
      * This is expressed in meters per squared second (m/s^2).
      */
     private double initialBiasZ;
 
     /**
      * Initial x scaling factor.
      */
     private double initialSx;
 
     /**
      * Initial y scaling factor.
      */
     private double initialSy;
 
     /**
      * Initial z scaling factor.
      */
     private double initialSz;
 
     /**
      * Initial x-y cross coupling error.
      */
     private double initialMxy;
 
     /**
      * Initial x-z cross coupling error.
      */
     private double initialMxz;
 
     /**
      * Initial y-x cross coupling error.
      */
     private double initialMyx;
 
     /**
      * Initial y-z cross coupling error.
      */
     private double initialMyz;
 
     /**
      * Initial z-x cross coupling error.
      */
     private double initialMzx;
 
     /**
      * Initial z-y cross coupling error.
      */
     private double initialMzy;
 
     /**
      * Indicates whether a linear calibrator is used or not for preliminary
      * solutions.
      */
     private boolean useLinearCalibrator = DEFAULT_USE_LINEAR_CALIBRATOR;
 
     /**
      * Indicates whether preliminary solutions must be refined after an initial linear solution
      * is found.
      */
     private boolean refinePreliminarySolutions = DEFAULT_REFINE_PRELIMINARY_SOLUTIONS;
 
     /**
      * Estimated accelerometer biases for each IMU axis expressed in meter per squared
      * second (m/s^2).
      */
     private double[] estimatedBiases;
 
     /**
      * Estimated accelerometer scale factors and cross coupling errors.
      * This is the product of matrix Ta containing cross coupling errors and Ka
      * containing scaling factors.
      * So tat:
      * <pre>
      *     Ma = [sx    mxy  mxz] = Ta*Ka
      *          [myx   sy   myz]
      *          [mzx   mzy  sz ]
      * </pre>
      * Where:
      * <pre>
      *     Ka = [sx 0   0 ]
      *          [0  sy  0 ]
      *          [0  0   sz]
      * </pre>
      * and
      * <pre>
      *     Ta = [1          -alphaXy    alphaXz ]
      *          [alphaYx    1           -alphaYz]
      *          [-alphaZx   alphaZy     1       ]
      * </pre>
      * Hence:
      * <pre>
      *     Ma = [sx    mxy  mxz] = Ta*Ka =  [sx             -sy * alphaXy   sz * alphaXz ]
      *          [myx   sy   myz]            [sx * alphaYx   sy              -sz * alphaYz]
      *          [mzx   mzy  sz ]            [-sx * alphaZx  sy * alphaZy    sz           ]
      * </pre>
      * This instance allows any 3x3 matrix however, typically alphaYx, alphaZx and alphaZy
      * are considered to be zero if the accelerometer z-axis is assumed to be the same
      * as the body z-axis. When this is assumed, myx = mzx = mzy = 0 and the Ma matrix
      * becomes upper diagonal:
      * <pre>
      *     Ma = [sx    mxy  mxz]
      *          [0     sy   myz]
      *          [0     0    sz ]
      * </pre>
      * Values of this matrix are unit-less.
      */
     private Matrix estimatedMa;
 
     /**
      * Indicates whether covariance must be kept after refining result.
      * This setting is only taken into account if result is refined.
      */
     private boolean keepCovariance = DEFAULT_KEEP_COVARIANCE;
 
     /**
      * Estimated covariance of estimated position.
      * This is only available when result has been refined and covariance is kept.
      */
     private Matrix estimatedCovariance;
 
     /**
      * Estimated chi square value.
      */
     private double estimatedChiSq;
 
     /**
      * Estimated mean square error respect to provided measurements.
      */
     private double estimatedMse;
 
     /**
      * Estimated degrees of freedom of chi square value. Degrees of freedom is equal to the number of sampled data
      * minus the number of estimated parameters.
      */
     private int estimatedChiSqDegreesOfFreedom;
 
     /**
      * Estimated reduced chi square value. This is equal to estimated chi square value divided by its degrees of
      * freedom. Ideally this value should be close to 1.0.
      */
     private double estimatedReducedChiSq;
 
     /**
      * Estimated probability of finding a smaller chi square value expressed as a value between 0.0 and 1.0. The smaller
      * the found chi square value is, the better the fit of the estimated parameters to the actual parameter. Thus, the
      * smaller the chance of finding a smaller chi square value, then the better the estimated fit is.
      */
     private double estimatedP;
 
     /**
      * Estimated measure of quality of estimated fit as a value between 0.0 and 1.0. The larger the quality value is,
      * the better the fit that has been estimated.
      */
     private double estimatedQ;
 
     /**
      * A linear least squares calibrator.
      */
     private final KnownFrameAccelerometerLinearLeastSquaresCalibrator linearCalibrator =
             new KnownFrameAccelerometerLinearLeastSquaresCalibrator();
 
     /**
      * A non-linear least squares calibrator.
      */
     private final KnownFrameAccelerometerNonLinearLeastSquaresCalibrator nonLinearCalibrator =
             new KnownFrameAccelerometerNonLinearLeastSquaresCalibrator();
 
     /**
      * Constructor.
      */
     protected RobustKnownFrameAccelerometerCalibrator() {
     }
 
     /**
      * Constructor.
      *
      * @param listener listener to be notified of events such as when estimation
      *                 starts, ends or its progress significantly changes.
      */
     protected RobustKnownFrameAccelerometerCalibrator(final RobustKnownFrameAccelerometerCalibratorListener listener) {
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements list of body kinematics measurements with standard
      *                     deviations taken at different frames (positions, orientations
      *                     and velocities).
      */
     protected RobustKnownFrameAccelerometerCalibrator(final List<StandardDeviationFrameBodyKinematics> measurements) {
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements list of body kinematics measurements with standard
      *                     deviations taken at different frames (positions, orientations
      *                     and velocities).
      * @param listener     listener to handle events raised by this calibrator.
      */
     protected RobustKnownFrameAccelerometerCalibrator(
             final List<StandardDeviationFrameBodyKinematics> measurements,
             final RobustKnownFrameAccelerometerCalibratorListener listener) {
         this(measurements);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      */
     protected RobustKnownFrameAccelerometerCalibrator(final boolean commonAxisUsed) {
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      */
     protected RobustKnownFrameAccelerometerCalibrator(
             final boolean commonAxisUsed, final RobustKnownFrameAccelerometerCalibratorListener listener) {
         this(commonAxisUsed);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      */
     protected RobustKnownFrameAccelerometerCalibrator(
             final List<StandardDeviationFrameBodyKinematics> measurements, final boolean commonAxisUsed) {
         this(measurements);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      */
     protected RobustKnownFrameAccelerometerCalibrator(
             final List<StandardDeviationFrameBodyKinematics> measurements, final boolean commonAxisUsed,
             final RobustKnownFrameAccelerometerCalibratorListener listener) {
         this(measurements, commonAxisUsed);
         this.listener = listener;
     }
 
     /**
      * Gets initial x-coordinate of accelerometer bias to be used to find a solutions.
      * This is expressed in meters per squared second (m/s^2) and only taken into
      * account if non-linear preliminary solutions are used.
      *
      * @return initial x-coordinate of accelerometer bias.
      */
     @Override
     public double getInitialBiasX() {
         return initialBiasX;
     }
 
     /**
      * Sets initial x-coordinate of accelerometer bias to be used to find a solution.
      * This is expressed in meters per squared second (m/s^2) and only taken into
      * account if non-linear preliminary solutions are used.
      *
      * @param initialBiasX initial x-coordinate of accelerometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialBiasX(final double initialBiasX) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialBiasX = initialBiasX;
     }
 
     /**
      * Gets initial y-coordinate of accelerometer bias to be used to find a solution.
      * This is expressed in meters per squared second (m/s^2) and only taken into
      * account if non-linear preliminary solutions are used.
      *
      * @return initial y-coordinate of accelerometer bias.
      */
     @Override
     public double getInitialBiasY() {
         return initialBiasY;
     }
 
     /**
      * Sets initial y-coordinate of accelerometer bias to be used to find a solution.
      * This is expressed in meters per squared second (m/s^2) and only taken into
      * account if non-linear preliminary solutions are used.
      *
      * @param initialBiasY initial y-coordinate of accelerometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialBiasY(final double initialBiasY) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialBiasY = initialBiasY;
     }
 
     /**
      * Gets initial z-coordinate of accelerometer bias to be used to find a solution.
      * This is expressed in meters per squared second (m/s^2) and only taken into
      * account if non-linear preliminary solutions are used.
      *
      * @return initial z-coordinate of accelerometer bias.
      */
     @Override
     public double getInitialBiasZ() {
         return initialBiasZ;
     }
 
     /**
      * Sets initial z-coordinate of accelerometer bias to be used to find a solution.
      * This is expressed in meters per squared second (m/s^2) and only taken into
      * account if non-linear preliminary solutions are used.
      *
      * @param initialBiasZ initial z-coordinate of accelerometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialBiasZ(final double initialBiasZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialBiasZ = initialBiasZ;
     }
 
     /**
      * Gets initial x-coordinate of accelerometer bias to be used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial x-coordinate of accelerometer bias.
      */
     @Override
     public Acceleration getInitialBiasXAsAcceleration() {
         return new Acceleration(initialBiasX, AccelerationUnit.METERS_PER_SQUARED_SECOND);
     }
 
     /**
      * Gets initial x-coordinate of accelerometer bias to be used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param result instance where result data will be stored.
      */
     @Override
     public void getInitialBiasXAsAcceleration(final Acceleration result) {
         result.setValue(initialBiasX);
         result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
     }
 
     /**
      * Sets initial x-coordinate of accelerometer bias to be used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialBiasX initial x-coordinate of accelerometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialBiasX(final Acceleration initialBiasX) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialBiasX = convertAcceleration(initialBiasX);
     }
 
     /**
      * Gets initial y-coordinate of accelerometer bias to be used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial y-coordinate of accelerometer bias.
      */
     @Override
     public Acceleration getInitialBiasYAsAcceleration() {
         return new Acceleration(initialBiasY, AccelerationUnit.METERS_PER_SQUARED_SECOND);
     }
 
     /**
      * Gets initial y-coordinate of accelerometer bias to be used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param result instance where result data will be stored.
      */
     @Override
     public void getInitialBiasYAsAcceleration(final Acceleration result) {
         result.setValue(initialBiasY);
         result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
     }
 
     /**
      * Sets initial y-coordinate of accelerometer bias to be used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialBiasY initial y-coordinate of accelerometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialBiasY(final Acceleration initialBiasY) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialBiasY = convertAcceleration(initialBiasY);
     }
 
     /**
      * Gets initial z-coordinate of accelerometer bias to be used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial z-coordinate of accelerometer bias.
      */
     @Override
     public Acceleration getInitialBiasZAsAcceleration() {
         return new Acceleration(initialBiasZ, AccelerationUnit.METERS_PER_SQUARED_SECOND);
     }
 
     /**
      * Gets initial z-coordinate of accelerometer bias to be used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param result instance where result data will be stored.
      */
     @Override
     public void getInitialBiasZAsAcceleration(final Acceleration result) {
         result.setValue(initialBiasZ);
         result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
     }
 
     /**
      * Sets initial z-coordinate of accelerometer bias to be used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialBiasZ initial z-coordinate of accelerometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialBiasZ(final Acceleration initialBiasZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialBiasZ = convertAcceleration(initialBiasZ);
     }
 
     /**
      * Sets initial bias coordinates of accelerometer used to find a solution
      * expressed in meters per squared second (m/s^2).
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialBiasX initial x-coordinate of accelerometer bias.
      * @param initialBiasY initial y-coordinate of accelerometer bias.
      * @param initialBiasZ initial z-coordinate of accelerometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialBias(final double initialBiasX, final double initialBiasY, final double initialBiasZ)
             throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialBiasX = initialBiasX;
         this.initialBiasY = initialBiasY;
         this.initialBiasZ = initialBiasZ;
     }
 
     /**
      * Sets initial bias coordinates of accelerometer used to find a solution.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialBiasX initial x-coordinate of accelerometer bias.
      * @param initialBiasY initial y-coordinate of accelerometer bias.
      * @param initialBiasZ initial z-coordinate of accelerometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialBias(final Acceleration initialBiasX, final Acceleration initialBiasY,
                                final Acceleration initialBiasZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialBiasX = convertAcceleration(initialBiasX);
         this.initialBiasY = convertAcceleration(initialBiasY);
         this.initialBiasZ = convertAcceleration(initialBiasZ);
     }
 
     /**
      * Gets initial bias coordinates of accelerometer used to find a solution.
      *
      * @return initial bias coordinates.
      */
     @Override
     public AccelerationTriad getInitialBiasAsTriad() {
         return new AccelerationTriad(AccelerationUnit.METERS_PER_SQUARED_SECOND,
                 initialBiasX, initialBiasY, initialBiasZ);
     }
 
     /**
      * Gets initial bias coordinates of accelerometer used to find a solution.
      *
      * @param result instance where result will be stored.
      */
     @Override
     public void getInitialBiasAsTriad(final AccelerationTriad result) {
         result.setValueCoordinatesAndUnit(initialBiasX, initialBiasY, initialBiasZ,
                 AccelerationUnit.METERS_PER_SQUARED_SECOND);
     }
 
     /**
      * Sets initial bias coordinates of accelerometer used to find a solution.
      *
      * @param initialBias initial bias coordinates to be set.
      */
     @Override
     public void setInitialBias(final AccelerationTriad initialBias) {
         initialBiasX = convertAcceleration(initialBias.getValueX(), initialBias.getUnit());
         initialBiasY = convertAcceleration(initialBias.getValueY(), initialBias.getUnit());
         initialBiasZ = convertAcceleration(initialBias.getValueZ(), initialBias.getUnit());
     }
 
     /**
      * Gets initial x scaling factor.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial x scaling factor.
      */
     @Override
     public double getInitialSx() {
         return initialSx;
     }
 
     /**
      * Sets initial x scaling factor.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialSx initial x scaling factor.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialSx(final double initialSx) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialSx = initialSx;
     }
 
     /**
      * Gets initial y scaling factor.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial y scaling factor.
      */
     @Override
     public double getInitialSy() {
         return initialSy;
     }
 
     /**
      * Sets initial y scaling factor.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialSy initial y scaling factor.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialSy(final double initialSy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialSy = initialSy;
     }
 
     /**
      * Gets initial z scaling factor.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial z scaling factor.
      */
     @Override
     public double getInitialSz() {
         return initialSz;
     }
 
     /**
      * Sets initial z scaling factor.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialSz initial z scaling factor.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialSz(final double initialSz) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialSz = initialSz;
     }
 
     /**
      * Gets initial x-y cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial x-y cross coupling error.
      */
     @Override
     public double getInitialMxy() {
         return initialMxy;
     }
 
     /**
      * Sets initial x-y cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialMxy initial x-y cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMxy(final double initialMxy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMxy = initialMxy;
     }
 
     /**
      * Gets initial x-z cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial x-z cross coupling error.
      */
     @Override
     public double getInitialMxz() {
         return initialMxz;
     }
 
     /**
      * Sets initial x-z cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialMxz initial x-z cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMxz(final double initialMxz) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMxz = initialMxz;
     }
 
     /**
      * Gets initial y-x cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial y-x cross coupling error.
      */
     @Override
     public double getInitialMyx() {
         return initialMyx;
     }
 
     /**
      * Sets initial y-x cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialMyx initial y-x cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMyx(final double initialMyx) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMyx = initialMyx;
     }
 
     /**
      * Gets initial y-z cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial y-z cross coupling error.
      */
     @Override
     public double getInitialMyz() {
         return initialMyz;
     }
 
     /**
      * Sets initial y-z cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialMyz initial y-z cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMyz(final double initialMyz) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMyz = initialMyz;
     }
 
     /**
      * Gets initial z-x cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial z-x cross coupling error.
      */
     @Override
     public double getInitialMzx() {
         return initialMzx;
     }
 
     /**
      * Sets initial z-x cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialMzx initial z-x cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMzx(final double initialMzx) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMzx = initialMzx;
     }
 
     /**
      * Gets initial z-y cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial z-y cross coupling error.
      */
     @Override
     public double getInitialMzy() {
         return initialMzy;
     }
 
     /**
      * Sets initial z-y cross coupling error.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialMzy initial z-y cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMzy(final double initialMzy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMzy = initialMzy;
     }
 
     /**
      * Sets initial scaling factors.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialSx initial x scaling factor.
      * @param initialSy initial y scaling factor.
      * @param initialSz initial z scaling factor.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialScalingFactors(
             final double initialSx, final double initialSy, final double initialSz) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialSx = initialSx;
         this.initialSy = initialSy;
         this.initialSz = initialSz;
     }
 
     /**
      * Sets initial cross coupling errors.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialMxy initial x-y cross coupling error.
      * @param initialMxz initial x-z cross coupling error.
      * @param initialMyx initial y-x cross coupling error.
      * @param initialMyz initial y-z cross coupling error.
      * @param initialMzx initial z-x cross coupling error.
      * @param initialMzy initial z-y cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialCrossCouplingErrors(
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMxy = initialMxy;
         this.initialMxz = initialMxz;
         this.initialMyx = initialMyx;
         this.initialMyz = initialMyz;
         this.initialMzx = initialMzx;
         this.initialMzy = initialMzy;
     }
 
     /**
      * Sets initial scaling factors and cross coupling errors.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialSx  initial x scaling factor.
      * @param initialSy  initial y scaling factor.
      * @param initialSz  initial z scaling factor.
      * @param initialMxy initial x-y cross coupling error.
      * @param initialMxz initial x-z cross coupling error.
      * @param initialMyx initial y-x cross coupling error.
      * @param initialMyz initial y-z cross coupling error.
      * @param initialMzx initial z-x cross coupling error.
      * @param initialMzy initial z-y cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialScalingFactorsAndCrossCouplingErrors(
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         setInitialScalingFactors(initialSx, initialSy, initialSz);
         setInitialCrossCouplingErrors(initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
     }
 
     /**
      * Gets initial bias to be used to find a solution as an array.
      * Array values are expressed in meters per squared second (m/s^2).
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return array containing coordinates of initial bias.
      */
     @Override
     public double[] getInitialBias() {
         final var result = new double[BodyKinematics.COMPONENTS];
         getInitialBias(result);
         return result;
     }
 
     /**
      * Gets initial bias to be used to find a solution as an array.
      * Array values are expressed in meters per squared second (m/s^2).
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param result instance where result data will be copied to.
      * @throws IllegalArgumentException if provided array does not have length 3.
      */
     @Override
     public void getInitialBias(final double[] result) {
         if (result.length != BodyKinematics.COMPONENTS) {
             throw new IllegalArgumentException();
         }
         result[0] = initialBiasX;
         result[1] = initialBiasY;
         result[2] = initialBiasZ;
     }
 
     /**
      * Sets initial bias to be used to find a solution as an array.
      * Array values are expressed in meters per squared second (m/s^2).
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialBias initial bias to find a solution.
      * @throws LockedException          if calibrator is currently running.
      * @throws IllegalArgumentException if provided array does not have length 3.
      */
     @Override
     public void setInitialBias(final double[] initialBias) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         if (initialBias.length != BodyKinematics.COMPONENTS) {
             throw new IllegalArgumentException();
         }
         initialBiasX = initialBias[0];
         initialBiasY = initialBias[1];
         initialBiasZ = initialBias[2];
     }
 
     /**
      * Gets initial bias to be used to find a solution as a column matrix.
      * This is only taken into account if non-linear preliminary solutions are used.
      * Values are expressed in meters per squared second (m/s^2).
      *
      * @return initial bias to be used to find a solution as a column matrix.
      */
     @Override
     public Matrix getInitialBiasAsMatrix() {
         Matrix result;
         try {
             result = new Matrix(BodyKinematics.COMPONENTS, 1);
             getInitialBiasAsMatrix(result);
         } catch (final WrongSizeException ignore) {
             // never happens
             result = null;
         }
         return result;
     }
 
     /**
      * Gets initial bias to be used to find a solution as a column matrix.
      * This is only taken into account if non-linear preliminary solutions are used.
      * Values are expressed in meters per squared second (m/s^2).
      *
      * @param result instance where result data will be copied to.
      * @throws IllegalArgumentException if provided matrix is not 3x1.
      */
     @Override
     public void getInitialBiasAsMatrix(final Matrix result) {
         if (result.getRows() != BodyKinematics.COMPONENTS || result.getColumns() != 1) {
             throw new IllegalArgumentException();
         }
         result.setElementAtIndex(0, initialBiasX);
         result.setElementAtIndex(1, initialBiasY);
         result.setElementAtIndex(2, initialBiasZ);
     }
 
     /**
      * Sets initial bias to be used to find a solution as an array.
      * This is only taken into account if non-linear preliminary solutions are used.
      * Values are expressed in meters per squared second (m/s^2).
      *
      * @param initialBias initial bias to find a solution.
      * @throws LockedException          if calibrator is currently running.
      * @throws IllegalArgumentException if provided matrix is not 3x1.
      */
     @Override
     public void setInitialBias(final Matrix initialBias) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (initialBias.getRows() != BodyKinematics.COMPONENTS || initialBias.getColumns() != 1) {
             throw new IllegalArgumentException();
         }
 
         initialBiasX = initialBias.getElementAtIndex(0);
         initialBiasY = initialBias.getElementAtIndex(1);
         initialBiasZ = initialBias.getElementAtIndex(2);
     }
 
     /**
      * Gets initial scale factors and cross coupling errors matrix.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @return initial scale factors and cross coupling errors matrix.
      */
     @Override
     public Matrix getInitialMa() {
         Matrix result;
         try {
             result = new Matrix(BodyKinematics.COMPONENTS, BodyKinematics.COMPONENTS);
             getInitialMa(result);
         } catch (final WrongSizeException ignore) {
             // never happens
             result = null;
         }
         return result;
     }
 
     /**
      * Gets initial scale factors and cross coupling errors matrix.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param result instance where data will be stored.
      * @throws IllegalArgumentException if provided matrix is not 3x3.
      */
     @Override
     public void getInitialMa(final Matrix result) {
         if (result.getRows() != BodyKinematics.COMPONENTS || result.getColumns() != BodyKinematics.COMPONENTS) {
             throw new IllegalArgumentException();
         }
         result.setElementAtIndex(0, initialSx);
         result.setElementAtIndex(1, initialMyx);
         result.setElementAtIndex(2, initialMzx);
 
         result.setElementAtIndex(3, initialMxy);
         result.setElementAtIndex(4, initialSy);
         result.setElementAtIndex(5, initialMzy);
 
         result.setElementAtIndex(6, initialMxz);
         result.setElementAtIndex(7, initialMyz);
         result.setElementAtIndex(8, initialSz);
     }
 
     /**
      * Sets initial scale factors and cross coupling errors matrix.
      * This is only taken into account if non-linear preliminary solutions are used.
      *
      * @param initialMa initial scale factors and cross coupling errors matrix.
      * @throws IllegalArgumentException if provided matrix is not 3x3.
      * @throws LockedException          if calibrator is currently running.
      */
     @Override
     public void setInitialMa(final Matrix initialMa) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (initialMa.getRows() != BodyKinematics.COMPONENTS || initialMa.getColumns() != BodyKinematics.COMPONENTS) {
             throw new IllegalArgumentException();
         }
 
         initialSx = initialMa.getElementAtIndex(0);
         initialMyx = initialMa.getElementAtIndex(1);
         initialMzx = initialMa.getElementAtIndex(2);
 
         initialMxy = initialMa.getElementAtIndex(3);
         initialSy = initialMa.getElementAtIndex(4);
         initialMzy = initialMa.getElementAtIndex(5);
 
         initialMxz = initialMa.getElementAtIndex(6);
         initialMyz = initialMa.getElementAtIndex(7);
         initialSz = initialMa.getElementAtIndex(8);
     }
 
     /**
      * Gets a list of body kinematics measurements taken at different
      * frames (positions, orientations and velocities) and containing the standard
      * deviations of accelerometer and gyroscope measurements.
      * If a single device IMU needs to be calibrated, typically all measurements are
      * taken at the same position, with zero velocity and multiple orientations.
      * However, if we just want to calibrate the a given IMU model (e.g. obtain
      * an average and less precise calibration for the IMU of a given phone model),
      * we could take measurements collected throughout the planet at multiple positions
      * while the phone remains static (e.g. while charging), hence each measurement
      * position will change, velocity will remain zero and orientation will be
      * typically constant at horizontal orientation while the phone remains on a
      * flat surface.
      *
      * @return a collection of body kinematics measurements taken at different
      * frames (positions, orientations and velocities).
      */
     @Override
     public List<StandardDeviationFrameBodyKinematics> getMeasurements() {
         return measurements;
     }
 
     /**
      * Sets a list of body kinematics measurements taken at different
      * frames (positions, orientations and velocities) and containing the standard
      * deviations of accelerometer and gyroscope measurements.
      * If a single device IMU needs to be calibrated, typically all measurements are
      * taken at the same position, with zero velocity and multiple orientations.
      * However, if we just want to calibrate the a given IMU model (e.g. obtain
      * an average and less precise calibration for the IMU of a given phone model),
      * we could take measurements collected throughout the planet at multiple positions
      * while the phone remains static (e.g. while charging), hence each measurement
      * position will change, velocity will remain zero and orientation will be
      * typically constant at horizontal orientation while the phone remains on a
      * flat surface.
      *
      * @param measurements collection of body kinematics measurements taken at different
      *                     frames (positions, orientations and velocities).
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setMeasurements(
             final List<StandardDeviationFrameBodyKinematics> measurements) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.measurements = measurements;
     }
 
     /**
      * Indicates the type of measurement used by this calibrator.
      *
      * @return type of measurement used by this calibrator.
      */
     @Override
     public AccelerometerCalibratorMeasurementType getMeasurementType() {
         return AccelerometerCalibratorMeasurementType.STANDARD_DEVIATION_FRAME_BODY_KINEMATICS;
     }
 
     /**
      * Indicates whether this calibrator requires ordered measurements in a
      * list or not.
      *
      * @return true if measurements must be ordered, false otherwise.
      */
     @Override
     public boolean isOrderedMeasurementsRequired() {
         return true;
     }
 
     /**
      * Indicates whether z-axis is assumed to be common for accelerometer and
      * gyroscope.
      * When enabled, this eliminates 3 variables from Ma matrix.
      *
      * @return true if z-axis is assumed to be common for accelerometer and gyroscope,
      * false otherwise.
      */
     @Override
     public boolean isCommonAxisUsed() {
         return commonAxisUsed;
     }
 
     /**
      * Specifies whether z-axis is assumed to be common for accelerometer and
      * gyroscope.
      * When enabled, this eliminates 3 variables from Ma matrix.
      *
      * @param commonAxisUsed true if z-axis is assumed to be common for accelerometer
      *                       and gyroscope, false otherwise.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setCommonAxisUsed(final boolean commonAxisUsed) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Gets listener to handle events raised by this estimator.
      *
      * @return listener to handle events raised by this estimator.
      */
     public RobustKnownFrameAccelerometerCalibratorListener getListener() {
         return listener;
     }
 
     /**
      * Sets listener to handle events raised by this estimator.
      *
      * @param listener listener to handle events raised by this estimator.
      * @throws LockedException if calibrator is currently running.
      */
     public void setListener(final RobustKnownFrameAccelerometerCalibratorListener listener) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         this.listener = listener;
     }
 
     /**
      * Gets minimum number of required measurements.
      *
      * @return minimum number of required measurements.
      */
     @Override
     public int getMinimumRequiredMeasurements() {
         return MINIMUM_MEASUREMENTS;
     }
 
     /**
      * Indicates whether calibrator is ready to start.
      *
      * @return true if calibrator is ready, false otherwise.
      */
     @Override
     public boolean isReady() {
         return measurements != null && measurements.size() >= MINIMUM_MEASUREMENTS;
     }
 
     /**
      * Indicates whether calibrator is currently running or not.
      *
      * @return true if calibrator is running, false otherwise.
      */
     @Override
     public boolean isRunning() {
         return running;
     }
 
     /**
      * Indicates whether a linear calibrator is used or not for preliminary
      * solutions.
      *
      * @return indicates whether a linear calibrator is used or not for
      * preliminary solutions.
      */
     public boolean isLinearCalibratorUsed() {
         return useLinearCalibrator;
     }
 
     /**
      * Specifies whether a linear calibrator is used or not for preliminary
      * solutions.
      *
      * @param linearCalibratorUsed indicates whether a linear calibrator is used
      *                             or not for preliminary solutions.
      * @throws LockedException if calibrator is currently running.
      */
     public void setLinearCalibratorUsed(final boolean linearCalibratorUsed) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         useLinearCalibrator = linearCalibratorUsed;
     }
 
     /**
      * Indicates whether preliminary solutions must be refined after an initial linear solution is found.
      * If no initial solution is found using a linear solver, a non linear solver will be
      * used regardless of this value using an average solution as the initial value to be
      * refined.
      *
      * @return true if preliminary solutions must be refined after an initial linear solution, false
      * otherwise.
      */
     public boolean isPreliminarySolutionRefined() {
         return refinePreliminarySolutions;
     }
 
     /**
      * Specifies whether preliminary solutions must be refined after an initial linear solution is found.
      * If no initial solution is found using a linear solver, a non linear solver will be
      * used regardless of this value using an average solution as the initial value to be
      * refined.
      *
      * @param preliminarySolutionRefined true if preliminary solutions must be refined after an
      *                                   initial linear solution, false otherwise.
      * @throws LockedException if calibrator is currently running.
      */
     public void setPreliminarySolutionRefined(final boolean preliminarySolutionRefined) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         refinePreliminarySolutions = preliminarySolutionRefined;
     }
 
     /**
      * Returns amount of progress variation before notifying a progress change during
      * calibration.
      *
      * @return amount of progress variation before notifying a progress change during
      * calibration.
      */
     public float getProgressDelta() {
         return progressDelta;
     }
 
     /**
      * Sets amount of progress variation before notifying a progress change during
      * calibration.
      *
      * @param progressDelta amount of progress variation before notifying a progress
      *                      change during calibration.
      * @throws IllegalArgumentException if progress delta is less than zero or greater than 1.
      * @throws LockedException          if calibrator is currently running.
      */
     public void setProgressDelta(final float progressDelta) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (progressDelta < MIN_PROGRESS_DELTA || progressDelta > MAX_PROGRESS_DELTA) {
             throw new IllegalArgumentException();
         }
         this.progressDelta = progressDelta;
     }
 
     /**
      * Returns amount of confidence expressed as a value between 0.0 and 1.0
      * (which is equivalent to 100%). The amount of confidence indicates the probability
      * that the estimated result is correct. Usually this value will be close to 1.0, but
      * not exactly 1.0.
      *
      * @return amount of confidence as a value between 0.0 and 1.0.
      */
     public double getConfidence() {
         return confidence;
     }
 
     /**
      * Sets amount of confidence expressed as a value between 0.0 and 1.0 (which is
      * equivalent to 100%). The amount of confidence indicates the probability that
      * the estimated result is correct. Usually this value will be close to 1.0, but
      * not exactly 1.0.
      *
      * @param confidence confidence to be set as a value between 0.0 and 1.0.
      * @throws IllegalArgumentException if provided value is not between 0.0 and 1.0.
      * @throws LockedException          if calibrator is currently running.
      */
     public void setConfidence(final double confidence) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (confidence < MIN_CONFIDENCE || confidence > MAX_CONFIDENCE) {
             throw new IllegalArgumentException();
         }
         this.confidence = confidence;
     }
 
     /**
      * Returns maximum allowed number of iterations. If maximum allowed number of
      * iterations is achieved without converging to a result when calling calibrate(),
      * a RobustEstimatorException will be raised.
      *
      * @return maximum allowed number of iterations.
      */
     public int getMaxIterations() {
         return maxIterations;
     }
 
     /**
      * Sets maximum allowed number of iterations. When the maximum number of iterations
      * is exceeded, result will not be available, however an approximate result will be
      * available for retrieval.
      *
      * @param maxIterations maximum allowed number of iterations to be set.
      * @throws IllegalArgumentException if provided value is less than 1.
      * @throws LockedException          if calibrator is currently running.
      */
     public void setMaxIterations(final int maxIterations) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (maxIterations < MIN_ITERATIONS) {
             throw new IllegalArgumentException();
         }
         this.maxIterations = maxIterations;
     }
 
     /**
      * Gets data related to inliers found after estimation.
      *
      * @return data related to inliers found after estimation.
      */
     public InliersData getInliersData() {
         return inliersData;
     }
 
     /**
      * Indicates whether result must be refined using a non-linear solver over found inliers.
      *
      * @return true to refine result, false to simply use result found by robust estimator
      * without further refining.
      */
     public boolean isResultRefined() {
         return refineResult;
     }
 
     /**
      * Specifies whether result must be refined using a non-linear solver over found inliers.
      *
      * @param refineResult true to refine result, false to simply use result found by robust
      *                     estimator without further refining.
      * @throws LockedException if calibrator is currently running.
      */
     public void setResultRefined(final boolean refineResult) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.refineResult = refineResult;
     }
 
     /**
      * Indicates whether covariance must be kept after refining result.
      * This setting is only taken into account if result is refined.
      *
      * @return true if covariance must be kept after refining result, false otherwise.
      */
     public boolean isCovarianceKept() {
         return keepCovariance;
     }
 
     /**
      * Specifies whether covariance must be kept after refining result.
      * This setting is only taken into account if result is refined.
      *
      * @param keepCovariance true if covariance must be kept after refining result,
      *                       false otherwise.
      * @throws LockedException if calibrator is currently running.
      */
     public void setCovarianceKept(final boolean keepCovariance) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.keepCovariance = keepCovariance;
     }
 
     /**
      * Returns quality scores corresponding to each measurement.
      * The larger the score value the better the quality of the sample.
      * This implementation always returns null.
      * Subclasses using quality scores must implement proper behavior.
      *
      * @return quality scores corresponding to each sample.
      */
     @Override
     public double[] getQualityScores() {
         return null;
     }
 
     /**
      * Sets quality scores corresponding to each measurement.
      * The larger the score value the better the quality of the sample.
      * This implementation makes no action.
      * Subclasses using quality scores must implement proper behaviour.
      *
      * @param qualityScores quality scores corresponding to each pair of
      *                      matched points.
      * @throws IllegalArgumentException if provided quality scores length
      *                                  is smaller than minimum required samples.
      * @throws LockedException          if calibrator is currently running.
      */
     @Override
     public void setQualityScores(final double[] qualityScores) throws LockedException {
     }
 
     /**
      * Gets array containing x,y,z components of estimated accelerometer biases
      * expressed in meters per squared second (m/s^2).
      *
      * @return array containing x,y,z components of estimated accelerometer biases.
      */
     @Override
     public double[] getEstimatedBiases() {
         return estimatedBiases;
     }
 
     /**
      * Gets array containing x,y,z components of estimated accelerometer biases
      * expressed in meters per squared second (m/s^2).
      *
      * @param result instance where estimated accelerometer biases will be stored.
      * @return true if result instance was updated, false otherwise (when estimation
      * is not yet available).
      */
     @Override
     public boolean getEstimatedBiases(final double[] result) {
         if (estimatedBiases != null) {
             System.arraycopy(estimatedBiases, 0, result, 0, estimatedBiases.length);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets column matrix containing x,y,z components of estimated accelerometer biases
      * expressed in meters per squared second (m/s^2).
      *
      * @return column matrix containing x,y,z components of estimated accelerometer
      * biases
      */
     @Override
     public Matrix getEstimatedBiasesAsMatrix() {
         return estimatedBiases != null ? Matrix.newFromArray(estimatedBiases) : null;
     }
 
     /**
      * Gets column matrix containing x,y,z components of estimated accelerometer biases
      * expressed in meters per squared second (m/s^2).
      *
      * @param result instance where result data will be stored.
      * @return true if result was updated, false otherwise.
      * @throws WrongSizeException if provided result instance has invalid size.
      */
     @Override
     public boolean getEstimatedBiasesAsMatrix(final Matrix result) throws WrongSizeException {
         if (estimatedBiases != null) {
             result.fromArray(estimatedBiases);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets x coordinate of estimated accelerometer bias expressed in meters per
      * squared second (m/s^2).
      *
      * @return x coordinate of estimated accelerometer bias or null if not available.
      */
     @Override
     public Double getEstimatedBiasFx() {
         return estimatedBiases != null ? estimatedBiases[0] : null;
     }
 
     /**
      * Gets y coordinate of estimated accelerometer bias expressed in meters per
      * squared second (m/s^2).
      *
      * @return y coordinate of estimated accelerometer bias or null if not available.
      */
     @Override
     public Double getEstimatedBiasFy() {
         return estimatedBiases != null ? estimatedBiases[1] : null;
     }
 
     /**
      * Gets z coordinate of estimated accelerometer bias expressed in meters per
      * squared second (m/s^2).
      *
      * @return z coordinate of estimated accelerometer bias or null if not available.
      */
     @Override
     public Double getEstimatedBiasFz() {
         return estimatedBiases != null ? estimatedBiases[2] : null;
     }
 
     /**
      * Gets x coordinate of estimated accelerometer bias.
      *
      * @return x coordinate of estimated accelerometer bias or null if not available.
      */
     @Override
     public Acceleration getEstimatedBiasFxAsAcceleration() {
         return estimatedBiases != null
                 ? new Acceleration(estimatedBiases[0], AccelerationUnit.METERS_PER_SQUARED_SECOND) : null;
     }
 
     /**
      * Gets x coordinate of estimated accelerometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if result was updated, false if estimation is not available.
      */
     @Override
     public boolean getEstimatedBiasFxAsAcceleration(final Acceleration result) {
         if (estimatedBiases != null) {
             result.setValue(estimatedBiases[0]);
             result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets y coordinate of estimated accelerometer bias.
      *
      * @return y coordinate of estimated accelerometer bias or null if not available.
      */
     @Override
     public Acceleration getEstimatedBiasFyAsAcceleration() {
         return estimatedBiases != null
                 ? new Acceleration(estimatedBiases[1], AccelerationUnit.METERS_PER_SQUARED_SECOND) : null;
     }
 
     /**
      * Gets y coordinate of estimated accelerometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if result was updated, false if estimation is not available.
      */
     @Override
     public boolean getEstimatedBiasFyAsAcceleration(final Acceleration result) {
         if (estimatedBiases != null) {
             result.setValue(estimatedBiases[1]);
             result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets z coordinate of estimated accelerometer bias.
      *
      * @return z coordinate of estimated accelerometer bias or null if not available.
      */
     @Override
     public Acceleration getEstimatedBiasFzAsAcceleration() {
         return estimatedBiases != null
                 ? new Acceleration(estimatedBiases[2], AccelerationUnit.METERS_PER_SQUARED_SECOND) : null;
     }
 
     /**
      * Gets z coordinate of estimated accelerometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if result was updated, false if estimation is not available.
      */
     @Override
     public boolean getEstimatedBiasFzAsAcceleration(final Acceleration result) {
         if (estimatedBiases != null) {
             result.setValue(estimatedBiases[2]);
             result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets estimated accelerometer bias.
      *
      * @return estimated accelerometer bias or null if not available.
      */
     @Override
     public AccelerationTriad getEstimatedBiasAsTriad() {
         return estimatedBiases != null
                 ? new AccelerationTriad(AccelerationUnit.METERS_PER_SQUARED_SECOND,
                 estimatedBiases[0], estimatedBiases[1], estimatedBiases[2])
                 : null;
     }
 
     /**
      * Gets estimated accelerometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if estimated accelerometer bias is available and result was
      * modified, false otherwise.
      */
     @Override
     public boolean getEstimatedBiasAsTriad(final AccelerationTriad result) {
         if (estimatedBiases != null) {
             result.setValueCoordinatesAndUnit(estimatedBiases[0], estimatedBiases[1], estimatedBiases[2],
                     AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets estimated accelerometer scale factors and ross coupling errors.
      * This is the product of matrix Ta containing cross coupling errors and Ka
      * containing scaling factors.
      * So tat:
      * <pre>
      *     Ma = [sx    mxy  mxz] = Ta*Ka
      *          [myx   sy   myz]
      *          [mzx   mzy  sz ]
      * </pre>
      * Where:
      * <pre>
      *     Ka = [sx 0   0 ]
      *          [0  sy  0 ]
      *          [0  0   sz]
      * </pre>
      * and
      * <pre>
      *     Ta = [1          -alphaXy    alphaXz ]
      *          [alphaYx    1           -alphaYz]
      *          [-alphaZx   alphaZy     1       ]
      * </pre>
      * Hence:
      * <pre>
      *     Ma = [sx    mxy  mxz] = Ta*Ka =  [sx             -sy * alphaXy   sz * alphaXz ]
      *          [myx   sy   myz]            [sx * alphaYx   sy              -sz * alphaYz]
      *          [mzx   mzy  sz ]            [-sx * alphaZx  sy * alphaZy    sz           ]
      * </pre>
      * This instance allows any 3x3 matrix however, typically alphaYx, alphaZx and alphaZy
      * are considered to be zero if the accelerometer z-axis is assumed to be the same
      * as the body z-axis. When this is assumed, myx = mzx = mzy = 0 and the Ma matrix
      * becomes upper diagonal:
      * <pre>
      *     Ma = [sx    mxy  mxz]
      *          [0     sy   myz]
      *          [0     0    sz ]
      * </pre>
      * Values of this matrix are unit-less.
      *
      * @return estimated accelerometer scale factors and cross coupling errors, or null
      * if not available.
      */
     @Override
     public Matrix getEstimatedMa() {
         return estimatedMa;
     }
 
     /**
      * Gets estimated x-axis scale factor.
      *
      * @return estimated x-axis scale factor or null if not available.
      */
     @Override
     public Double getEstimatedSx() {
         return estimatedMa != null ? estimatedMa.getElementAt(0, 0) : null;
     }
 
     /**
      * Gets estimated y-axis scale factor.
      *
      * @return estimated y-axis scale factor or null if not available.
      */
     @Override
     public Double getEstimatedSy() {
         return estimatedMa != null ? estimatedMa.getElementAt(1, 1) : null;
     }
 
     /**
      * Gets estimated z-axis scale factor.
      *
      * @return estimated z-axis scale factor or null if not available.
      */
     @Override
     public Double getEstimatedSz() {
         return estimatedMa != null ? estimatedMa.getElementAt(2, 2) : null;
     }
 
     /**
      * Gets estimated x-y cross-coupling error.
      *
      * @return estimated x-y cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMxy() {
         return estimatedMa != null ? estimatedMa.getElementAt(0, 1) : null;
     }
 
     /**
      * Gets estimated x-z cross-coupling error.
      *
      * @return estimated x-z cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMxz() {
         return estimatedMa != null ? estimatedMa.getElementAt(0, 2) : null;
     }
 
     /**
      * Gets estimated y-x cross-coupling error.
      *
      * @return estimated y-x cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMyx() {
         return estimatedMa != null ? estimatedMa.getElementAt(1, 0) : null;
     }
 
     /**
      * Gets estimated y-z cross-coupling error.
      *
      * @return estimated y-z cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMyz() {
         return estimatedMa != null ? estimatedMa.getElementAt(1, 2) : null;
     }
 
     /**
      * Gets estimated z-x cross-coupling error.
      *
      * @return estimated z-x cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMzx() {
         return estimatedMa != null ? estimatedMa.getElementAt(2, 0) : null;
     }
 
     /**
      * Gets estimated z-y cross-coupling error.
      *
      * @return estimated z-y cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMzy() {
         return estimatedMa != null ? estimatedMa.getElementAt(2, 1) : null;
     }
 
     /**
      * Gets estimated chi square value.
      *
      * @return estimated chi square value.
      */
     @Override
     public double getEstimatedChiSq() {
         return estimatedChiSq;
     }
 
     /**
      * Gets estimated chi square degrees of freedom. Degrees of freedom is equal to the number of sampled data minus the
      * number of estimated parameters.
      *
      * @return estimated degrees of freedom of chi square value
      */
     @Override
     public int getEstimatedChiSqDegreesOfFreedom() {
         return estimatedChiSqDegreesOfFreedom;
     }
 
     /**
      * Gets estimated reduced chi square value. This is equal to estimated chi square value divided by its degrees of
      * freedom. Ideally this value should be close to 1.0, indicating that fit is optimal.
      * A value larger than 1.0 indicates that fit is not good or noise has been underestimated, and a value smaller than
      * 1.0 indicates that there is overfitting or noise has been overestimated.
      *
      * @return estimated reduced chi square value
      */
     @Override
     public double getEstimatedReducedChiSq() {
         return estimatedReducedChiSq;
     }
 
     /**
      * Gets estimated probability of finding a smaller chi square value expressed as a value between 0.0 and 1.0. The
      * smaller the found chi square value is, the better the fit of the estimated parameters to the actual parameter.
      * Thus, the smaller the chance of finding a smaller chi square value, then the better the estimated fit is.
      *
      * @return estimated probability of finding a smaller chi square value.
      */
     @Override
     public double getEstimatedP() {
         return estimatedP;
     }
 
     /**
      * Gets estimated measure of quality of estimated fit as a value between 0.0 and 1.0. The larger the quality value
      * is, the better the fit that has been estimated.
      *
      * @return estimated measure of quality of estimated fit.
      */
     @Override
     public double getEstimatedQ() {
         return estimatedQ;
     }
 
     /**
      * Gets estimated mean square error respect to provided measurements.
      *
      * @return estimated mean square error respect to provided measurements.
      */
     @Override
     public double getEstimatedMse() {
         return estimatedMse;
     }
 
     /**
      * Gets estimated covariance matrix for estimated calibration solution.
      * Diagonal elements of the matrix contains variance for the following
      * parameters (following indicated order): bx, by, bz, sx, sy, sz,
      * mxy, mxz, myx, myz, mzx, mzy.
      * This is only available when result has been refined and covariance
      * is kept.
      *
      * @return estimated covariance matrix for estimated position.
      */
     @Override
     public Matrix getEstimatedCovariance() {
         return estimatedCovariance;
     }
 
     /**
      * Gets variance of estimated x coordinate of accelerometer bias expressed in (m^2/s^4).
      *
      * @return variance of estimated x coordinate of accelerometer bias or null if not available.
      */
     public Double getEstimatedBiasFxVariance() {
         return estimatedCovariance != null ? estimatedCovariance.getElementAt(0, 0) : null;
     }
 
     /**
      * Gets standard deviation of estimated x coordinate of accelerometer bias expressed in
      * meters per squared second (m/s^2).
      *
      * @return standard deviation of estimated x coordinate of accelerometer bias or null if not
      * available.
      */
     public Double getEstimatedBiasFxStandardDeviation() {
         final var variance = getEstimatedBiasFxVariance();
         return variance != null ? Math.sqrt(variance) : null;
     }
 
     /**
      * Gets standard deviation of estimated x coordinate of accelerometer bias.
      *
      * @return standard deviation of estimated x coordinate of accelerometer bias or null if not
      * available.
      */
     public Acceleration getEstimatedBiasFxStandardDeviationAsAcceleration() {
         return estimatedCovariance != null
                 ? new Acceleration(getEstimatedBiasFxStandardDeviation(), AccelerationUnit.METERS_PER_SQUARED_SECOND)
                 : null;
     }
 
     /**
      * Gets standard deviation of estimated x coordinate of accelerometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if standard deviation of estimated x coordinate of accelerometer bias is available,
      * false otherwise.
      */
     public boolean getEstimatedBiasFxStandardDeviationAsAcceleration(final Acceleration result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedBiasFxStandardDeviation());
             result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets variance of estimated y coordinate of accelerometer bias expressed in (m^2/s^4).
      *
      * @return variance of estimated y coordinate of accelerometer bias or null if not available.
      */
     public Double getEstimatedBiasFyVariance() {
         return estimatedCovariance != null ? estimatedCovariance.getElementAt(1, 1) : null;
     }
 
     /**
      * Gets standard deviation of estimated y coordinate of accelerometer bias expressed in
      * meters per squared second (m/s^2).
      *
      * @return standard deviation of estimated y coordinate of accelerometer bias or null if not
      * available.
      */
     public Double getEstimatedBiasFyStandardDeviation() {
         final var variance = getEstimatedBiasFyVariance();
         return variance != null ? Math.sqrt(variance) : null;
     }
 
     /**
      * Gets standard deviation of estimated y coordinate of accelerometer bias.
      *
      * @return standard deviation of estimated y coordinate of accelerometer bias or null if not
      * available.
      */
     public Acceleration getEstimatedBiasFyStandardDeviationAsAcceleration() {
         return estimatedCovariance != null
                 ? new Acceleration(getEstimatedBiasFyStandardDeviation(), AccelerationUnit.METERS_PER_SQUARED_SECOND)
                 : null;
     }
 
     /**
      * Gets standard deviation of estimated y coordinate of accelerometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if standard deviation of estimated y coordinate of accelerometer bias is available,
      * false otherwise.
      */
     public boolean getEstimatedBiasFyStandardDeviationAsAcceleration(final Acceleration result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedBiasFyStandardDeviation());
             result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets variance of estimated z coordinate of accelerometer bias expressed in (m^2/s^4).
      *
      * @return variance of estimated z coordinate of accelerometer bias or null if not available.
      */
     public Double getEstimatedBiasFzVariance() {
         return estimatedCovariance != null ? estimatedCovariance.getElementAt(2, 2) : null;
     }
 
     /**
      * Gets standard deviation of estimated z coordinate of accelerometer bias expressed in
      * meters per squared second (m/s^2).
      *
      * @return standard deviation of estimated z coordinate of accelerometer bias or null if not
      * available.
      */
     public Double getEstimatedBiasFzStandardDeviation() {
         final var variance = getEstimatedBiasFzVariance();
         return variance != null ? Math.sqrt(variance) : null;
     }
 
     /**
      * Gets standard deviation of estimated z coordinate of accelerometer bias.
      *
      * @return standard deviation of estimated z coordinate of accelerometer bias or null if not
      * available.
      */
     public Acceleration getEstimatedBiasFzStandardDeviationAsAcceleration() {
         return estimatedCovariance != null
                 ? new Acceleration(getEstimatedBiasFzStandardDeviation(), AccelerationUnit.METERS_PER_SQUARED_SECOND)
                 : null;
     }
 
     /**
      * Gets standard deviation of estimated z coordinate of accelerometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if standard deviation of estimated z coordinate of accelerometer bias is available,
      * false otherwise.
      */
     public boolean getEstimatedBiasFzStandardDeviationAsAcceleration(final Acceleration result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedBiasFzStandardDeviation());
             result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets standard deviation of estimated accelerometer bias coordinates.
      *
      * @return standard deviation of estimated accelerometer bias coordinates.
      */
     public AccelerationTriad getEstimatedBiasStandardDeviation() {
         return estimatedCovariance != null
                 ? new AccelerationTriad(AccelerationUnit.METERS_PER_SQUARED_SECOND,
                 getEstimatedBiasFxStandardDeviation(),
                 getEstimatedBiasFyStandardDeviation(),
                 getEstimatedBiasFzStandardDeviation())
                 : null;
     }
 
     /**
      * Gets standard deviation of estimated accelerometer bias coordinates.
      *
      * @param result instance where result will be stored.
      * @return true if standard deviation of accelerometer bias was available, false
      * otherwise.
      */
     public boolean getEstimatedBiasStandardDeviation(final AccelerationTriad result) {
         if (estimatedCovariance != null) {
             result.setValueCoordinatesAndUnit(
                     getEstimatedBiasFxStandardDeviation(),
                     getEstimatedBiasFyStandardDeviation(),
                     getEstimatedBiasFzStandardDeviation(),
                     AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets average of estimated standard deviation of accelerometer bias coordinates expressed
      * in meters per squared second (m/s^2).
      *
      * @return average of estimated standard deviation of accelerometer bias coordinates or null
      * if not available.
      */
     public Double getEstimatedBiasStandardDeviationAverage() {
         return estimatedCovariance != null
                 ? (getEstimatedBiasFxStandardDeviation() + getEstimatedBiasFyStandardDeviation()
                 + getEstimatedBiasFzStandardDeviation()) / 3.0
                 : null;
     }
 
     /**
      * Gets average of estimated standard deviation of accelerometer bias coordinates.
      *
      * @return average of estimated standard deviation of accelerometer bias coordinates or null.
      */
     public Acceleration getEstimatedBiasStandardDeviationAverageAsAcceleration() {
         return estimatedCovariance != null
                 ? new Acceleration(getEstimatedBiasStandardDeviationAverage(),
                 AccelerationUnit.METERS_PER_SQUARED_SECOND)
                 : null;
     }
 
     /**
      * Gets average of estimated standard deviation of accelerometer bias coordinates.
      *
      * @param result instance where result will be stored.
      * @return true if average of estimated standard deviation of accelerometer bias is available,
      * false otherwise.
      */
     public boolean getEstimatedBiasStandardDeviationAverageAsAcceleration(final Acceleration result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedBiasStandardDeviationAverage());
             result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets norm of estimated standard deviation of accelerometer bias expressed in
      * meters per squared second (m/s^2).
      * This can be used as the initial accelerometer bias uncertainty for
      * {@link INSLooselyCoupledKalmanInitializerConfig} or {@link INSTightlyCoupledKalmanInitializerConfig}.
      *
      * @return norm of estimated standard deviation of accelerometer bias or null
      * if not available.
      */
     @Override
     public Double getEstimatedBiasStandardDeviationNorm() {
         return estimatedCovariance != null
                 ? Math.sqrt(getEstimatedBiasFxVariance() + getEstimatedBiasFyVariance() + getEstimatedBiasFzVariance())
                 : null;
     }
 
     /**
      * Gets norm of estimated standard deviation of accelerometer bias.
      * This can be used as the initial accelerometer bias uncertainty for
      * {@link INSLooselyCoupledKalmanInitializerConfig} or {@link INSTightlyCoupledKalmanInitializerConfig}.
      *
      * @return norm of estimated standard deviation of accelerometer bias or null
      * if not available.
      */
     public Acceleration getEstimatedBiasStandardDeviationNormAsAcceleration() {
         return estimatedCovariance != null
                 ? new Acceleration(getEstimatedBiasStandardDeviationNorm(), AccelerationUnit.METERS_PER_SQUARED_SECOND)
                 : null;
     }
 
     /**
      * Gets norm of estimated standard deviation of accelerometer bias coordinates.
      * This can be used as the initial accelerometer bias uncertainty for
      * {@link INSLooselyCoupledKalmanInitializerConfig} or {@link INSTightlyCoupledKalmanInitializerConfig}.
      *
      * @param result instance where result will be stored.
      * @return true if norm of estimated standard deviation of accelerometer bias is
      * available, false otherwise.
      */
     public boolean getEstimatedBiasStandardDeviationNormAsAcceleration(final Acceleration result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedBiasStandardDeviationNorm());
             result.setUnit(AccelerationUnit.METERS_PER_SQUARED_SECOND);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets size of subsets to be checked during robust estimation.
      * This has to be at least {@link #MINIMUM_MEASUREMENTS}.
      *
      * @return size of subsets to be checked during robust estimation.
      */
     public int getPreliminarySubsetSize() {
         return preliminarySubsetSize;
     }
 
     /**
      * Sets size of subsets to be checked during robust estimation.
      * This has to be at least {@link #MINIMUM_MEASUREMENTS}.
      *
      * @param preliminarySubsetSize size of subsets to be checked during robust estimation.
      * @throws LockedException          if calibrator is currently running.
      * @throws IllegalArgumentException if provided value is less than {@link #MINIMUM_MEASUREMENTS}.
      */
     public void setPreliminarySubsetSize(
             final int preliminarySubsetSize) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (preliminarySubsetSize < MINIMUM_MEASUREMENTS) {
             throw new IllegalArgumentException();
         }
 
         this.preliminarySubsetSize = preliminarySubsetSize;
     }
 
     /**
      * Returns method being used for robust estimation.
      *
      * @return method being used for robust estimation.
      */
     public abstract RobustEstimatorMethod getMethod();
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param method robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator();
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator();
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator();
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator();
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator();
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param listener listener to be notified of events such as when estimation
      *                 starts, ends or its progress significantly changes.
      * @param method   robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final RobustKnownFrameAccelerometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(listener);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(listener);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(listener);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(listener);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(listener);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param measurements list of body kinematics measurements with standard
      *                     deviations taken at different frames (positions, orientations
      *                     and velocities).
      * @param method       robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final List<StandardDeviationFrameBodyKinematics> measurements, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(measurements);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(measurements);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(measurements);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(measurements);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(measurements);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param measurements list of body kinematics measurements with standard
      *                     deviations taken at different frames (positions, orientations
      *                     and velocities).
      * @param listener     listener to handle events raised by this calibrator.
      * @param method       robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final List<StandardDeviationFrameBodyKinematics> measurements,
             final RobustKnownFrameAccelerometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(measurements, listener);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(measurements, listener);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(measurements, listener);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(measurements, listener);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(measurements, listener);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param method         robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final boolean commonAxisUsed, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(commonAxisUsed);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(commonAxisUsed);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      * @param method         robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final boolean commonAxisUsed, final RobustKnownFrameAccelerometerCalibratorListener listener,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed, listener);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(commonAxisUsed, listener);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed, listener);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed, listener);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(commonAxisUsed, listener);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param method         robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final List<StandardDeviationFrameBodyKinematics> measurements, final boolean commonAxisUsed,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      * @param method         robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final List<StandardDeviationFrameBodyKinematics> measurements, final boolean commonAxisUsed,
             final RobustKnownFrameAccelerometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed, listener);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed, listener);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed, listener);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed, listener);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed, listener);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param qualityScores quality scores corresponding to each provided
      *                      measurement. The larger the score value the better
      *                      the quality of the sample.
      * @param method        robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator();
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator();
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator();
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(qualityScores);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(qualityScores);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param qualityScores quality scores corresponding to each provided
      *                      measurement. The larger the score value the better
      *                      the quality of the sample.
      * @param listener      listener to be notified of events such as when estimation
      *                      starts, ends or its progress significantly changes.
      * @param method        robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final RobustKnownFrameAccelerometerCalibratorListener listener,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(listener);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(listener);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(listener);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(qualityScores, listener);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(qualityScores, listener);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param qualityScores quality scores corresponding to each provided
      *                      measurement. The larger the score value the better
      *                      the quality of the sample.
      * @param measurements  list of body kinematics measurements with standard
      *                      deviations taken at different frames (positions, orientations
      *                      and velocities).
      * @param method        robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyKinematics> measurements,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(measurements);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(measurements);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(measurements);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(qualityScores, measurements);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(qualityScores, measurements);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param qualityScores quality scores corresponding to each provided
      *                      measurement. The larger the score value the better
      *                      the quality of the sample.
      * @param measurements  list of body kinematics measurements with standard
      *                      deviations taken at different frames (positions, orientations
      *                      and velocities).
      * @param listener      listener to handle events raised by this calibrator.
      * @param method        robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyKinematics> measurements,
             final RobustKnownFrameAccelerometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(measurements, listener);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(measurements, listener);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(measurements, listener);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(qualityScores, measurements, listener);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(qualityScores, measurements, listener);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param qualityScores  quality scores corresponding to each provided
      *                       measurement. The larger the score value the better
      *                       the quality of the sample.
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param method         robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final boolean commonAxisUsed, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(commonAxisUsed);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(qualityScores, commonAxisUsed);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(qualityScores, commonAxisUsed);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param qualityScores  quality scores corresponding to each provided
      *                       measurement. The larger the score value the better
      *                       the quality of the sample.
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      * @param method         robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final boolean commonAxisUsed,
             final RobustKnownFrameAccelerometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed, listener);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(commonAxisUsed, listener);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(commonAxisUsed, listener);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(qualityScores, commonAxisUsed, listener);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(qualityScores, commonAxisUsed, listener);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param qualityScores  quality scores corresponding to each provided
      *                       measurement. The larger the score value the better
      *                       the quality of the sample.
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param method         robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyKinematics> measurements,
             final boolean commonAxisUsed, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(
                     qualityScores, measurements, commonAxisUsed);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(
                     qualityScores, measurements, commonAxisUsed);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator.
      *
      * @param qualityScores  quality scores corresponding to each provided
      *                       measurement. The larger the score value the better
      *                       the quality of the sample.
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      * @param method         robust estimator method.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyKinematics> measurements,
             final boolean commonAxisUsed, final RobustKnownFrameAccelerometerCalibratorListener listener,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed, listener);
             case LMEDS -> new LMedSRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed, listener);
             case MSAC -> new MSACRobustKnownFrameAccelerometerCalibrator(measurements, commonAxisUsed, listener);
             case PROSAC -> new PROSACRobustKnownFrameAccelerometerCalibrator(
                     qualityScores, measurements, commonAxisUsed, listener);
             default -> new PROMedSRobustKnownFrameAccelerometerCalibrator(
                     qualityScores, measurements, commonAxisUsed, listener);
         };
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create() {
         return create(DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param listener listener to be notified of events such as when estimation
      *                 starts, ends or its progress significantly changes.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final RobustKnownFrameAccelerometerCalibratorListener listener) {
         return create(listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param measurements list of body kinematics measurements with standard
      *                     deviations taken at different frames (positions, orientations
      *                     and velocities).
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final List<StandardDeviationFrameBodyKinematics> measurements) {
         return create(measurements, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param measurements list of body kinematics measurements with standard
      *                     deviations taken at different frames (positions, orientations
      *                     and velocities).
      * @param listener     listener to handle events raised by this calibrator.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final List<StandardDeviationFrameBodyKinematics> measurements,
             final RobustKnownFrameAccelerometerCalibratorListener listener) {
         return create(measurements, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(final boolean commonAxisUsed) {
         return create(commonAxisUsed, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final boolean commonAxisUsed, final RobustKnownFrameAccelerometerCalibratorListener listener) {
         return create(commonAxisUsed, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final List<StandardDeviationFrameBodyKinematics> measurements, final boolean commonAxisUsed) {
         return create(measurements, commonAxisUsed, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final List<StandardDeviationFrameBodyKinematics> measurements, final boolean commonAxisUsed,
             final RobustKnownFrameAccelerometerCalibratorListener listener) {
         return create(measurements, commonAxisUsed, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param qualityScores quality scores corresponding to each provided
      *                      measurement. The larger the score value the better
      *                      the quality of the sample.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(final double[] qualityScores) {
         return create(qualityScores, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param qualityScores quality scores corresponding to each provided
      *                      measurement. The larger the score value the better
      *                      the quality of the sample.
      * @param listener      listener to be notified of events such as when estimation
      *                      starts, ends or its progress significantly changes.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final RobustKnownFrameAccelerometerCalibratorListener listener) {
         return create(qualityScores, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param qualityScores quality scores corresponding to each provided
      *                      measurement. The larger the score value the better
      *                      the quality of the sample.
      * @param measurements  list of body kinematics measurements with standard
      *                      deviations taken at different frames (positions, orientations
      *                      and velocities).
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyKinematics> measurements) {
         return create(qualityScores, measurements, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param qualityScores quality scores corresponding to each provided
      *                      measurement. The larger the score value the better
      *                      the quality of the sample.
      * @param measurements  list of body kinematics measurements with standard
      *                      deviations taken at different frames (positions, orientations
      *                      and velocities).
      * @param listener      listener to handle events raised by this calibrator.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyKinematics> measurements,
             final RobustKnownFrameAccelerometerCalibratorListener listener) {
         return create(qualityScores, measurements, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param qualityScores  quality scores corresponding to each provided
      *                       measurement. The larger the score value the better
      *                       the quality of the sample.
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final boolean commonAxisUsed) {
         return create(qualityScores, commonAxisUsed, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param qualityScores  quality scores corresponding to each provided
      *                       measurement. The larger the score value the better
      *                       the quality of the sample.
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final boolean commonAxisUsed,
             final RobustKnownFrameAccelerometerCalibratorListener listener) {
         return create(qualityScores, commonAxisUsed, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param qualityScores  quality scores corresponding to each provided
      *                       measurement. The larger the score value the better
      *                       the quality of the sample.
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyKinematics> measurements,
             final boolean commonAxisUsed) {
         return create(qualityScores, measurements, commonAxisUsed, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust accelerometer calibrator using default robust method.
      *
      * @param qualityScores  quality scores corresponding to each provided
      *                       measurement. The larger the score value the better
      *                       the quality of the sample.
      * @param measurements   list of body kinematics measurements with standard
      *                       deviations taken at different frames (positions, orientations
      *                       and velocities).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common for
      *                       accelerometer and gyroscope.
      * @param listener       listener to handle events raised by this calibrator.
      * @return a robust accelerometer calibrator.
      */
     public static RobustKnownFrameAccelerometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyKinematics> measurements,
             final boolean commonAxisUsed, final RobustKnownFrameAccelerometerCalibratorListener listener) {
         return create(qualityScores, measurements, commonAxisUsed, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Computes error of a preliminary result respect a given measurement.
      *
      * @param measurement       a measurement.
      * @param preliminaryResult a preliminary result.
      * @return computed error.
      */
     protected double computeError(
             final StandardDeviationFrameBodyKinematics measurement, final PreliminaryResult preliminaryResult) {
         // We know that measured specific force is:
         // fmeas = ba + (I + Ma) * ftrue
 
         // Hence:
         // [fmeasx] = [bx] + ( [1  0   0] + [sx    mxy mxz])   [ftruex]
         // [fmeasy]   [by]     [0  1   0]   [myx   sy  myz]    [ftruey]
         // [fmeasz]   [bz]     [0  0   1]   [mzx   mzy sz ]    [ftruez]
 
         final var measuredKinematics = measurement.getKinematics();
         final var ecefFrame = measurement.getFrame();
         final var previousEcefFrame = measurement.getPreviousFrame();
         final var timeInterval = measurement.getTimeInterval();
 
         final var expectedKinematics = ECEFKinematicsEstimator.estimateKinematicsAndReturnNew(
                 timeInterval, ecefFrame, previousEcefFrame);
 
         final var fMeasX1 = measuredKinematics.getFx();
         final var fMeasY1 = measuredKinematics.getFy();
         final var fMeasZ1 = measuredKinematics.getFz();
 
         final var fTrueX = expectedKinematics.getFx();
         final var fTrueY = expectedKinematics.getFy();
         final var fTrueZ = expectedKinematics.getFz();
 
         final var b = preliminaryResult.estimatedBiases;
         final var bx = b[0];
         final var by = b[1];
         final var bz = b[2];
 
         final var ma = preliminaryResult.estimatedMa;
 
         try {
             final var m = Matrix.identity(BodyKinematics.COMPONENTS, BodyKinematics.COMPONENTS);
             m.add(ma);
 
             final var ftrue = new Matrix(BodyKinematics.COMPONENTS, 1);
             ftrue.setElementAtIndex(0, fTrueX);
             ftrue.setElementAtIndex(1, fTrueY);
             ftrue.setElementAtIndex(2, fTrueZ);
 
             m.multiply(ftrue);
 
             final var fMeasX2 = bx + m.getElementAtIndex(0);
             final var fMeasY2 = by + m.getElementAtIndex(1);
             final var fMeasZ2 = bz + m.getElementAtIndex(2);
 
             final var diffX = fMeasX2 - fMeasX1;
             final var diffY = fMeasY2 - fMeasY1;
             final var diffZ = fMeasZ2 - fMeasZ1;
 
             return Math.sqrt(diffX * diffX + diffY * diffY + diffZ * diffZ);
 
         } catch (final WrongSizeException e) {
             return Double.MAX_VALUE;
         }
     }
 
     /**
      * Computes a preliminary solution for a subset of samples picked by a robust estimator.
      *
      * @param samplesIndices indices of samples picked by the robust estimator.
      * @param solutions      list where estimated preliminary solution will be stored.
      */
     protected void computePreliminarySolutions(final int[] samplesIndices, final List<PreliminaryResult> solutions) {
 
         final var meas = new ArrayList<StandardDeviationFrameBodyKinematics>();
 
         for (final var samplesIndex : samplesIndices) {
             meas.add(measurements.get(samplesIndex));
         }
 
         try {
             final var result = new PreliminaryResult();
             result.estimatedBiases = getInitialBias();
             result.estimatedMa = getInitialMa();
 
             if (useLinearCalibrator) {
                 linearCalibrator.setCommonAxisUsed(commonAxisUsed);
                 linearCalibrator.setMeasurements(meas);
                 linearCalibrator.calibrate();
 
                 linearCalibrator.getEstimatedBiases(result.estimatedBiases);
                 result.estimatedMa = linearCalibrator.getEstimatedMa();
             }
 
             if (refinePreliminarySolutions) {
                 nonLinearCalibrator.setInitialBias(result.estimatedBiases);
                 nonLinearCalibrator.setInitialMa(result.estimatedMa);
                 nonLinearCalibrator.setCommonAxisUsed(commonAxisUsed);
                 nonLinearCalibrator.setMeasurements(meas);
                 nonLinearCalibrator.calibrate();
 
                 nonLinearCalibrator.getEstimatedBiases(result.estimatedBiases);
                 result.estimatedMa = nonLinearCalibrator.getEstimatedMa();
 
                 if (keepCovariance) {
                     result.covariance = nonLinearCalibrator.getEstimatedCovariance();
                 } else {
                     result.covariance = null;
                 }
 
                 result.estimatedMse = nonLinearCalibrator.getEstimatedMse();
                 result.estimatedChiSq = nonLinearCalibrator.getEstimatedChiSq();
                 result.estimatedChiSqDegreesOfFreedom = nonLinearCalibrator.getEstimatedChiSqDegreesOfFreedom();
                 result.estimatedReducedChiSq = nonLinearCalibrator.getEstimatedReducedChiSq();
                 result.estimatedP = nonLinearCalibrator.getEstimatedP();
                 result.estimatedQ = nonLinearCalibrator.getEstimatedQ();
             }
 
             solutions.add(result);
         } catch (final LockedException | CalibrationException | NotReadyException e) {
             solutions.clear();
         }
     }
 
     /**
      * Attempts to refine calibration parameters if refinement is requested.
      * This method returns a refined solution or provided input if refinement is not
      * requested or has failed.
      * If refinement is enabled and it is requested to keep covariance, this method
      * will also keep covariance of refined position.
      *
      * @param preliminaryResult a preliminary result.
      */
     protected void attemptRefine(final PreliminaryResult preliminaryResult) {
         if (refineResult && inliersData != null) {
             final var inliers = inliersData.getInliers();
             final var nSamples = measurements.size();
 
             final var inlierMeasurements = new ArrayList<StandardDeviationFrameBodyKinematics>();
             for (var i = 0; i < nSamples; i++) {
                 if (inliers.get(i)) {
                     // sample is inlier
                     inlierMeasurements.add(measurements.get(i));
                 }
             }
 
             try {
                 nonLinearCalibrator.setInitialBias(preliminaryResult.estimatedBiases);
                 nonLinearCalibrator.setInitialMa(preliminaryResult.estimatedMa);
                 nonLinearCalibrator.setCommonAxisUsed(commonAxisUsed);
                 nonLinearCalibrator.setMeasurements(inlierMeasurements);
                 nonLinearCalibrator.calibrate();
 
                 estimatedBiases = nonLinearCalibrator.getEstimatedBiases();
                 estimatedMa = nonLinearCalibrator.getEstimatedMa();
                 estimatedMse = nonLinearCalibrator.getEstimatedMse();
                 estimatedChiSq = nonLinearCalibrator.getEstimatedChiSq();
                 estimatedChiSqDegreesOfFreedom = nonLinearCalibrator.getEstimatedChiSqDegreesOfFreedom();
                 estimatedReducedChiSq = nonLinearCalibrator.getEstimatedReducedChiSq();
                 estimatedP = nonLinearCalibrator.getEstimatedP();
                 estimatedQ = nonLinearCalibrator.getEstimatedQ();
 
                 if (keepCovariance) {
                     estimatedCovariance = nonLinearCalibrator.getEstimatedCovariance();
                 } else {
                     estimatedCovariance = null;
                 }
 
             } catch (final LockedException | CalibrationException | NotReadyException e) {
                 estimatedCovariance = preliminaryResult.covariance;
                 estimatedBiases = preliminaryResult.estimatedBiases;
                 estimatedMa = preliminaryResult.estimatedMa;
                 estimatedMse = preliminaryResult.estimatedMse;
                 estimatedChiSq = preliminaryResult.estimatedChiSq;
                 estimatedChiSqDegreesOfFreedom = preliminaryResult.estimatedChiSqDegreesOfFreedom;
                 estimatedReducedChiSq = preliminaryResult.estimatedReducedChiSq;
                 estimatedP = preliminaryResult.estimatedP;
                 estimatedQ = preliminaryResult.estimatedQ;
             }
         } else {
             estimatedCovariance = preliminaryResult.covariance;
             estimatedBiases = preliminaryResult.estimatedBiases;
             estimatedMa = preliminaryResult.estimatedMa;
             estimatedMse = preliminaryResult.estimatedMse;
             estimatedChiSq = preliminaryResult.estimatedChiSq;
             estimatedChiSqDegreesOfFreedom = preliminaryResult.estimatedChiSqDegreesOfFreedom;
             estimatedReducedChiSq = preliminaryResult.estimatedReducedChiSq;
             estimatedP = preliminaryResult.estimatedP;
             estimatedQ = preliminaryResult.estimatedQ;
         }
     }
 
     /**
      * Converts acceleration value and unit to meters per squared second.
      *
      * @param value acceleration value.
      * @param unit  unit of acceleration value.
      * @return converted value.
      */
     private static double convertAcceleration(final double value, final AccelerationUnit unit) {
         return AccelerationConverter.convert(value, unit, AccelerationUnit.METERS_PER_SQUARED_SECOND);
     }
 
     /**
      * Converts acceleration instance to meters per squared second.
      *
      * @param acceleration acceleration instance to be converted.
      * @return converted value.
      */
     private static double convertAcceleration(final Acceleration acceleration) {
         return convertAcceleration(acceleration.getValue().doubleValue(), acceleration.getUnit());
     }
 
     /**
      * Internal class containing estimated preliminary result.
      */
     protected static class PreliminaryResult {
         /**
          * Estimated accelerometer biases for each IMU axis expressed in meter per squared
          * second (m/s^2).
          */
         private double[] estimatedBiases;
 
         /**
          * Estimated accelerometer scale factors and cross coupling errors.
          * This is the product of matrix Ta containing cross coupling errors and Ka
          * containing scaling factors.
          * So tat:
          * <pre>
          *     Ma = [sx    mxy  mxz] = Ta*Ka
          *          [myx   sy   myz]
          *          [mzx   mzy  sz ]
          * </pre>
          * Where:
          * <pre>
          *     Ka = [sx 0   0 ]
          *          [0  sy  0 ]
          *          [0  0   sz]
          * </pre>
          * and
          * <pre>
          *     Ta = [1          -alphaXy    alphaXz ]
          *          [alphaYx    1           -alphaYz]
          *          [-alphaZx   alphaZy     1       ]
          * </pre>
          * Hence:
          * <pre>
          *     Ma = [sx    mxy  mxz] = Ta*Ka =  [sx             -sy * alphaXy   sz * alphaXz ]
          *          [myx   sy   myz]            [sx * alphaYx   sy              -sz * alphaYz]
          *          [mzx   mzy  sz ]            [-sx * alphaZx  sy * alphaZy    sz           ]
          * </pre>
          * This instance allows any 3x3 matrix however, typically alphaYx, alphaZx and alphaZy
          * are considered to be zero if the accelerometer z-axis is assumed to be the same
          * as the body z-axis. When this is assumed, myx = mzx = mzy = 0 and the Ma matrix
          * becomes upper diagonal:
          * <pre>
          *     Ma = [sx    mxy  mxz]
          *          [0     sy   myz]
          *          [0     0    sz ]
          * </pre>
          * Values of this matrix are unit-less.
          */
         private Matrix estimatedMa;
 
         /**
          * Estimated covariance matrix.
          */
         private Matrix covariance;
 
         /**
          * Estimated MSE (Mean Square Error).
          */
         private double estimatedMse;
 
         /**
          * Estimated chi square value.
          */
         private double estimatedChiSq;
 
         /**
          * Estimated degrees of freedom of chi square value. Degrees of freedom is equal to the number of sampled data
          * minus the number of estimated parameters.
          */
         private int estimatedChiSqDegreesOfFreedom;
 
         /**
          * Estimated reduced chi square value. This is equal to estimated chi square value divided by its degrees of
          * freedom. Ideally this value should be close to 1.0.
          */
         private double estimatedReducedChiSq;
 
         /**
          * Estimated probability of finding a smaller chi square value expressed as a value between 0.0 and 1.0. The smaller
          * the found chi square value is, the better the fit of the estimated parameters to the actual parameter. Thus, the
          * smaller the chance of finding a smaller chi square value, then the better the estimated fit is.
          */
         private double estimatedP;
 
         /**
          * Estimated measure of quality of estimated fit as a value between 0.0 and 1.0. The larger the quality value is,
          * the better the fit that has been estimated.
          */
         private double estimatedQ;
     }
 }