/*
    * 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.magnetometer;
  
  import com.irurueta.algebra.Matrix;
  import com.irurueta.algebra.WrongSizeException;
  import com.irurueta.navigation.LockedException;
  import com.irurueta.navigation.NotReadyException;
  import com.irurueta.navigation.frames.CoordinateTransformation;
  import com.irurueta.navigation.frames.FrameType;
  import com.irurueta.navigation.frames.converters.ECEFtoNEDFrameConverter;
  import com.irurueta.navigation.inertial.BodyKinematics;
  import com.irurueta.navigation.inertial.BodyMagneticFluxDensity;
  import com.irurueta.navigation.inertial.calibration.CalibrationException;
  import com.irurueta.navigation.inertial.calibration.MagneticFluxDensityTriad;
  import com.irurueta.navigation.inertial.calibration.StandardDeviationFrameBodyMagneticFluxDensity;
  import com.irurueta.navigation.inertial.estimators.BodyMagneticFluxDensityEstimator;
  import com.irurueta.navigation.inertial.wmm.WMMEarthMagneticFluxDensityEstimator;
  import com.irurueta.navigation.inertial.wmm.WorldMagneticModel;
  import com.irurueta.numerical.robust.InliersData;
  import com.irurueta.numerical.robust.RobustEstimatorMethod;
  import com.irurueta.units.MagneticFluxDensity;
  import com.irurueta.units.MagneticFluxDensityConverter;
  import com.irurueta.units.MagneticFluxDensityUnit;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * This is an abstract class to robustly estimate magnetometer
   * hard-iron biases, soft-iron cross couplings and scaling factors.
   * <p>
   * To use this calibrator at least 4 measurements at different known
   * frames must be provided. In other words, magnetometer samples must
   * be obtained at 4 different positions or orientations.
   * Notice that frame velocities are ignored by this calibrator.
   * <p>
   * Measured magnetic flux density is assumed to follow the model shown below:
   * <pre>
   *     mBmeas = bm + (I + Mm) * mBtrue + w
   * </pre>
   * Where:
   * - mBmeas is the measured magnetic flux density. This is a 3x1 vector.
   * - bm is magnetometer hard-iron bias. Ideally, on a perfect magnetometer,
   * this should be a 3x1 zero vector.
   * - I is the 3x3 identity matrix.
   * - Mm is the 3x3 soft-iron matrix containing cross-couplings and scaling
   * factors. Ideally, on a perfect magnetometer, this should be a 3x3 zero
   * matrix.
   * - mBtrue is ground-truth magnetic flux density. This is a 3x1 vector.
   * - w is measurement noise. This is a 3x1 vector.
   */
  public abstract class RobustKnownFrameMagnetometerCalibrator implements MagnetometerNonLinearCalibrator,
          UnknownHardIronNonLinearMagnetometerCalibrator,
          OrderedStandardDeviationFrameBodyMagneticFluxDensityMagnetometerCalibrator,
          QualityScoredMagnetometerCalibrator {
  
      /**
       * Indicates whether by default a common z-axis is assumed for the accelerometer,
       * gyroscope and magnetometer.
       */
      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 magnetic flux density measurements taken
      * at different frames (positions and orientations) and containing the
      * standard deviation of magnetometer measurements.
      * If a single device magnetometer 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 magnetometer model (e.g.
      * obtain an average and less precise calibration for the magnetometer 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<StandardDeviationFrameBodyMagneticFluxDensity> measurements;
 
     /**
      * Listener to be notified of events such as when calibration starts, ends or its
      * progress significantly changes.
      */
     protected RobustKnownFrameMagnetometerCalibratorListener listener;
 
     /**
      * Indicates whether estimator 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 inlier 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,
      * gyroscope and magnetometer.
      * When enabled, this eliminates 3 variables from soft-iron (Mm) matrix.
      */
     private boolean commonAxisUsed = DEFAULT_USE_COMMON_Z_AXIS;
 
     /**
      * Initial x-coordinate of hard-iron bias to be used to find a solution.
      * This is expressed in Teslas (T).
      */
     private double initialHardIronX;
 
     /**
      * Initial y-coordinate of hard-iron bias to be used to find a solution.
      * This is expressed in Teslas (T).
      */
     private double initialHardIronY;
 
     /**
      * Initial z-coordinate of hard-iron bias to be used to find a solution.
      * This is expressed in Teslas (T).
      */
     private double initialHardIronZ;
 
     /**
      * 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 magnetometer hard-iron biases for each magnetometer axis
      * expressed in Teslas (T).
      */
     private double[] estimatedHardIron;
 
     /**
      * Estimated magnetometer soft-iron matrix containing scale factors
      * and cross coupling errors.
      * This is the product of matrix Tm containing cross coupling errors and Km
      * containing scaling factors.
      * So tat:
      * <pre>
      *     Mm = [sx    mxy  mxz] = Tm*Km
      *          [myx   sy   myz]
      *          [mzx   mzy  sz ]
      * </pre>
      * Where:
      * <pre>
      *     Km = [sx 0   0 ]
      *          [0  sy  0 ]
      *          [0  0   sz]
      * </pre>
      * and
      * <pre>
      *     Tm = [1          -alphaXy    alphaXz ]
      *          [alphaYx    1           -alphaYz]
      *          [-alphaZx   alphaZy     1       ]
      * </pre>
      * Hence:
      * <pre>
      *     Mm = [sx    mxy  mxz] = Tm*Km =  [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 Mm matrix
      * becomes upper diagonal:
      * <pre>
      *     Mm = [sx    mxy  mxz]
      *          [0     sy   myz]
      *          [0     0    sz ]
      * </pre>
      * Values of this matrix are unit-less.
      */
     private Matrix estimatedMm;
 
     /**
      * 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 matrix for estimated parameters.
      */
     private Matrix estimatedCovariance;
 
     /**
      * 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 mean square error respect to provided measurements.
      */
     private double estimatedMse;
 
     /**
      * 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;
 
     /**
      * Contains Earth's magnetic model.
      */
     private WorldMagneticModel magneticModel;
 
     /**
      * A linear least squares calibrator.
      */
     private final KnownFrameMagnetometerLinearLeastSquaresCalibrator linearCalibrator =
             new KnownFrameMagnetometerLinearLeastSquaresCalibrator();
 
     /**
      * A non-linear least squares calibrator.
      */
     private final KnownFrameMagnetometerNonLinearLeastSquaresCalibrator nonLinearCalibrator =
             new KnownFrameMagnetometerNonLinearLeastSquaresCalibrator();
 
     /**
      * World Magnetic Model estimator.
      */
     private WMMEarthMagneticFluxDensityEstimator wmmEstimator;
 
     /**
      * Constructor.
      */
     protected RobustKnownFrameMagnetometerCalibrator() {
     }
 
     /**
      * Constructor.
      *
      * @param listener listener to be notified of events such as when estimation
      *                 starts, ends or its progress significantly changes.
      */
     protected RobustKnownFrameMagnetometerCalibrator(final RobustKnownFrameMagnetometerCalibratorListener listener) {
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements list of body magnetic flux density measurements with standard
      *                     deviations taken at different frames (positions and
      *                     orientations).
      */
     protected RobustKnownFrameMagnetometerCalibrator(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements) {
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements list of body magnetic flux density measurements with standard
      *                     deviations taken at different frames (positions and
      *                     orientations).
      * @param listener     listener to handle events raised by this calibrator.
      */
     protected RobustKnownFrameMagnetometerCalibrator(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final RobustKnownFrameMagnetometerCalibratorListener listener) {
         this(measurements);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      */
     protected RobustKnownFrameMagnetometerCalibrator(final boolean commonAxisUsed) {
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      */
     protected RobustKnownFrameMagnetometerCalibrator(
             final boolean commonAxisUsed, final RobustKnownFrameMagnetometerCalibratorListener listener) {
         this(commonAxisUsed);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   list of body magnetic flux density measurements with standard
      *                       deviations taken at different frames (positions and
      *                       orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      */
     protected RobustKnownFrameMagnetometerCalibrator(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed) {
         this(measurements);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   list of body magnetic flux density measurements with standard
      *                       deviations taken at different frames (positions and
      *                       orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      */
     protected RobustKnownFrameMagnetometerCalibrator(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final RobustKnownFrameMagnetometerCalibratorListener listener) {
         this(measurements, commonAxisUsed);
         this.listener = listener;
     }
 
     /**
      * Gets initial x-coordinate of magnetometer hard-iron bias to be used
      * to find a solution.
      * This is expressed in Teslas (T).
      *
      * @return initial x-coordinate of magnetometer hard-iron bias.
      */
     @Override
     public double getInitialHardIronX() {
         return initialHardIronX;
     }
 
     /**
      * Sets initial x-coordinate of magnetometer hard-iron bias to be used
      * to find a solution.
      * This is expressed in Teslas (T).
      *
      * @param initialHardIronX initial x-coordinate of magnetometer
      *                         hard-iron bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialHardIronX(final double initialHardIronX) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialHardIronX = initialHardIronX;
     }
 
     /**
      * Gets initial y-coordinate of magnetometer hard-iron bias to be used
      * to find a solution.
      * This is expressed in Teslas (T).
      *
      * @return initial y-coordinate of magnetometer hard-iron bias.
      */
     @Override
     public double getInitialHardIronY() {
         return initialHardIronY;
     }
 
     /**
      * Sets initial y-coordinate of magnetometer hard-iron bias to be used
      * to find a solution.
      * This is expressed in Teslas (T).
      *
      * @param initialHardIronY initial y-coordinate of magnetometer
      *                         hard-iron bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialHardIronY(final double initialHardIronY) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialHardIronY = initialHardIronY;
     }
 
     /**
      * Gets initial z-coordinate of magnetometer hard-iron bias to be used
      * to find a solution.
      * This is expressed in Teslas (T).
      *
      * @return initial z-coordinate of magnetometer hard-iron bias.
      */
     @Override
     public double getInitialHardIronZ() {
         return initialHardIronZ;
     }
 
     /**
      * Sets initial z-coordinate of magnetometer hard-iron bias to be used
      * to find a solution.
      * This is expressed in meters Teslas (T).
      *
      * @param initialHardIronZ initial z-coordinate of magnetometer
      *                         hard-iron bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialHardIronZ(final double initialHardIronZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialHardIronZ = initialHardIronZ;
     }
 
     /**
      * Gets initial x-coordinate of magnetometer hard iron bias to be used
      * to find a solution.
      *
      * @return initial x-coordinate of magnetometer hard-iron bias.
      */
     @Override
     public MagneticFluxDensity getInitialHardIronXAsMagneticFluxDensity() {
         return new MagneticFluxDensity(initialHardIronX, MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Gets initial x-coordinate of magnetometer hard iron bias to be used
      * to find a solution.
      *
      * @param result instance where result will be stored.
      */
     @Override
     public void getInitialHardIronXAsMagneticFluxDensity(final MagneticFluxDensity result) {
         result.setValue(initialHardIronX);
         result.setUnit(MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Sets initial x-coordinate of magnetometer hard iron bias to be used
      * to find a solution.
      *
      * @param initialHardIronX initial x-coordinate of magnetometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialHardIronX(final MagneticFluxDensity initialHardIronX) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialHardIronX = convertMagneticFluxDensity(initialHardIronX);
     }
 
     /**
      * Gets initial y-coordinate of magnetometer hard iron bias to be used
      * to find a solution.
      *
      * @return initial y-coordinate of magnetometer hard-iron bias.
      */
     @Override
     public MagneticFluxDensity getInitialHardIronYAsMagneticFluxDensity() {
         return new MagneticFluxDensity(initialHardIronY, MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Gets initial y-coordinate of magnetometer hard iron bias to be used
      * to find a solution.
      *
      * @param result instance where result will be stored.
      */
     @Override
     public void getInitialHardIronYAsMagneticFluxDensity(final MagneticFluxDensity result) {
         result.setValue(initialHardIronY);
         result.setUnit(MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Sets initial y-coordinate of magnetometer hard iron bias to be used
      * to find a solution.
      *
      * @param initialHardIronY initial y-coordinate of magnetometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialHardIronY(final MagneticFluxDensity initialHardIronY) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialHardIronY = convertMagneticFluxDensity(initialHardIronY);
     }
 
     /**
      * Gets initial z-coordinate of magnetometer hard iron bias to be used
      * to find a solution.
      *
      * @return initial z-coordinate of magnetometer hard-iron bias.
      */
     @Override
     public MagneticFluxDensity getInitialHardIronZAsMagneticFluxDensity() {
         return new MagneticFluxDensity(initialHardIronZ, MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Gets initial z-coordinate of magnetometer hard iron bias to be used
      * to find a solution.
      *
      * @param result instance where result will be stored.
      */
     @Override
     public void getInitialHardIronZAsMagneticFluxDensity(final MagneticFluxDensity result) {
         result.setValue(initialHardIronZ);
         result.setUnit(MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Sets initial z-coordinate of magnetometer hard iron bias to be used
      * to find a solution.
      *
      * @param initialHardIronZ initial z-coordinate of magnetometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialHardIronZ(final MagneticFluxDensity initialHardIronZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialHardIronZ = convertMagneticFluxDensity(initialHardIronZ);
     }
 
     /**
      * Sets initial hard-iron bias coordinates of magnetometer used to find
      * a solution expressed in Teslas (T).
      *
      * @param initialHardIronX initial x-coordinate of magnetometer
      *                         hard-iron bias.
      * @param initialHardIronY initial y-coordinate of magnetometer
      *                         hard-iron bias.
      * @param initialHardIronZ initial z-coordinate of magnetometer
      *                         hard-iron bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialHardIron(
             final double initialHardIronX, final double initialHardIronY, final double initialHardIronZ)
             throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialHardIronX = initialHardIronX;
         this.initialHardIronY = initialHardIronY;
         this.initialHardIronZ = initialHardIronZ;
     }
 
     /**
      * Sets initial hard iron coordinates of magnetometer used to find a solution.
      *
      * @param initialHardIronX initial x-coordinate of magnetometer bias.
      * @param initialHardIronY initial y-coordinate of magnetometer bias.
      * @param initialHardIronZ initial z-coordinate of magnetometer bias.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialHardIron(
             final MagneticFluxDensity initialHardIronX, final MagneticFluxDensity initialHardIronY,
             final MagneticFluxDensity initialHardIronZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         this.initialHardIronX = convertMagneticFluxDensity(initialHardIronX);
         this.initialHardIronY = convertMagneticFluxDensity(initialHardIronY);
         this.initialHardIronZ = convertMagneticFluxDensity(initialHardIronZ);
     }
 
     /**
      * Gets initial hard-iron used to find a solution.
      *
      * @return initial hard-iron.
      */
     @Override
     public MagneticFluxDensityTriad getInitialHardIronAsTriad() {
         return new MagneticFluxDensityTriad(MagneticFluxDensityUnit.TESLA,
                 initialHardIronX, initialHardIronY, initialHardIronZ);
     }
 
     /**
      * Gets initial hard-iron used to find a solution.
      *
      * @param result instance where result will be stored.
      */
     @Override
     public void getInitialHardIronAsTriad(final MagneticFluxDensityTriad result) {
         result.setValueCoordinatesAndUnit(initialHardIronX, initialHardIronY, initialHardIronZ,
                 MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Sets initial hard-iron used to find a solution.
      *
      * @param initialHardIron initial hard-iron to be set.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialHardIron(final MagneticFluxDensityTriad initialHardIron) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         initialHardIronX = convertMagneticFluxDensity(initialHardIron.getValueX(), initialHardIron.getUnit());
         initialHardIronY = convertMagneticFluxDensity(initialHardIron.getValueY(), initialHardIron.getUnit());
         initialHardIronZ = convertMagneticFluxDensity(initialHardIron.getValueZ(), initialHardIron.getUnit());
     }
 
     /**
      * Gets initial x scaling factor.
      *
      * @return initial x scaling factor.
      */
     @Override
     public double getInitialSx() {
         return initialSx;
     }
 
     /**
      * Sets initial x scaling factor.
      *
      * @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.
      *
      * @return initial y scaling factor.
      */
     @Override
     public double getInitialSy() {
         return initialSy;
     }
 
     /**
      * Sets initial y scaling factor.
      *
      * @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.
      *
      * @return initial z scaling factor.
      */
     @Override
     public double getInitialSz() {
         return initialSz;
     }
 
     /**
      * Sets initial z scaling factor.
      *
      * @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.
      *
      * @return initial x-y cross coupling error.
      */
     @Override
     public double getInitialMxy() {
         return initialMxy;
     }
 
     /**
      * Sets initial x-y cross coupling error.
      *
      * @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.
      *
      * @return initial x-z cross coupling error.
      */
     @Override
     public double getInitialMxz() {
         return initialMxz;
     }
 
     /**
      * Sets initial x-z cross coupling error.
      *
      * @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.
      *
      * @return initial y-x cross coupling error.
      */
     @Override
     public double getInitialMyx() {
         return initialMyx;
     }
 
     /**
      * Sets initial y-x cross coupling error.
      *
      * @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.
      *
      * @return initial y-z cross coupling error.
      */
     @Override
     public double getInitialMyz() {
         return initialMyz;
     }
 
     /**
      * Sets initial y-z cross coupling error.
      *
      * @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.
      *
      * @return initial z-x cross coupling error.
      */
     @Override
     public double getInitialMzx() {
         return initialMzx;
     }
 
     /**
      * Sets initial z-x cross coupling error.
      *
      * @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.
      *
      * @return initial z-y cross coupling error.
      */
     @Override
     public double getInitialMzy() {
         return initialMzy;
     }
 
     /**
      * Sets initial z-y cross coupling error.
      *
      * @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.
      *
      * @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.
      *
      * @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.
      *
      * @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 hard-iron bias to be used to find a solution as an array.
      * Array values are expressed in Teslas (T).
      *
      * @return array containing coordinates of initial bias.
      */
     @Override
     public double[] getInitialHardIron() {
         final var result = new double[BodyMagneticFluxDensity.COMPONENTS];
         getInitialHardIron(result);
         return result;
     }
 
     /**
      * Gets initial hard-iron bias to be used to find a solution as an array.
      * Array values are expressed in Teslas (T).
      *
      * @param result instance where result data will be copied to.
      * @throws IllegalArgumentException if provided array does not have
      *                                  length 3.
      */
     @Override
     public void getInitialHardIron(final double[] result) {
         if (result.length != BodyMagneticFluxDensity.COMPONENTS) {
             throw new IllegalArgumentException();
         }
         result[0] = initialHardIronX;
         result[1] = initialHardIronY;
         result[2] = initialHardIronZ;
     }
 
     /**
      * Sets initial hard-iron bias to be used to find a solution as an array.
      * Array values are expressed in Teslas (T).
      *
      * @param initialHardIron initial hard-iron to find a solution.
      * @throws LockedException          if calibrator is currently running.
      * @throws IllegalArgumentException if provided array does not have length 3.
      */
     @Override
     public void setInitialHardIron(final double[] initialHardIron) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         if (initialHardIron.length != BodyMagneticFluxDensity.COMPONENTS) {
             throw new IllegalArgumentException();
         }
         initialHardIronX = initialHardIron[0];
         initialHardIronY = initialHardIron[1];
         initialHardIronZ = initialHardIron[2];
     }
 
     /**
      * Gets initial hard-iron bias to be used to find a solution as a
      * column matrix.
      * Values are expressed in Teslas (T).
      *
      * @return initial hard-iron bias to be used to find a solution as a
      * column matrix.
      */
     @Override
     public Matrix getInitialHardIronAsMatrix() {
         Matrix result;
         try {
             result = new Matrix(BodyMagneticFluxDensity.COMPONENTS, 1);
             getInitialHardIronAsMatrix(result);
         } catch (final WrongSizeException ignore) {
             // never happens
             result = null;
         }
         return result;
     }
 
     /**
      * Gets initial hard-iron bias to be used to find a solution as a
      * column matrix.
      * Values are expressed in Teslas (T).
      *
      * @param result instance where result data will be copied to.
      * @throws IllegalArgumentException if provided matrix is not 3x1.
      */
     @Override
     public void getInitialHardIronAsMatrix(final Matrix result) {
         if (result.getRows() != BodyMagneticFluxDensity.COMPONENTS || result.getColumns() != 1) {
             throw new IllegalArgumentException();
         }
         result.setElementAtIndex(0, initialHardIronX);
         result.setElementAtIndex(1, initialHardIronY);
         result.setElementAtIndex(2, initialHardIronZ);
     }
 
     /**
      * Sets initial hard-iron bias to be used to find a solution as a column
      * matrix with values expressed in Teslas (T).
      *
      * @param initialHardIron initial hard-iron bias to find a solution.
      * @throws LockedException          if calibrator is currently running.
      * @throws IllegalArgumentException if provided matrix is not 3x1.
      */
     @Override
     public void setInitialHardIron(final Matrix initialHardIron) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (initialHardIron.getRows() != BodyMagneticFluxDensity.COMPONENTS || initialHardIron.getColumns() != 1) {
             throw new IllegalArgumentException();
         }
 
         initialHardIronX = initialHardIron.getElementAtIndex(0);
         initialHardIronY = initialHardIron.getElementAtIndex(1);
         initialHardIronZ = initialHardIron.getElementAtIndex(2);
     }
 
     /**
      * Gets initial scale factors and cross coupling errors matrix.
      *
      * @return initial scale factors and cross coupling errors matrix.
      */
     @Override
     public Matrix getInitialMm() {
         Matrix result;
         try {
             result = new Matrix(BodyMagneticFluxDensity.COMPONENTS, BodyMagneticFluxDensity.COMPONENTS);
             getInitialMm(result);
         } catch (final WrongSizeException ignore) {
             // never happens
             result = null;
         }
         return result;
     }
 
     /**
      * Gets initial scale factors and cross coupling errors matrix.
      *
      * @param result instance where data will be stored.
      * @throws IllegalArgumentException if provided matrix is not 3x3.
      */
     @Override
     public void getInitialMm(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.
      *
      * @param initialMm 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 setInitialMm(final Matrix initialMm) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (initialMm.getRows() != BodyKinematics.COMPONENTS || initialMm.getColumns() != BodyKinematics.COMPONENTS) {
             throw new IllegalArgumentException();
         }
 
         initialSx = initialMm.getElementAtIndex(0);
         initialMyx = initialMm.getElementAtIndex(1);
         initialMzx = initialMm.getElementAtIndex(2);
 
         initialMxy = initialMm.getElementAtIndex(3);
         initialSy = initialMm.getElementAtIndex(4);
         initialMzy = initialMm.getElementAtIndex(5);
 
         initialMxz = initialMm.getElementAtIndex(6);
         initialMyz = initialMm.getElementAtIndex(7);
         initialSz = initialMm.getElementAtIndex(8);
     }
 
     /**
      * Gets a list of body magnetic flux density measurements taken at different
      * frames (positions, orientations and velocities).
      * 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.
      *
      * @return a collection of body magnetic flux density measurements taken at different
      * frames (positions, orientations and velocities).
      */
     @Override
     public List<StandardDeviationFrameBodyMagneticFluxDensity> getMeasurements() {
         return measurements;
     }
 
     /**
      * Sets a list of body magnetic flux density measurements taken at different
      * frames (positions, orientations and velocities).
      * 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 magnetic flux density measurements
      *                     taken at different frames (positions, orientations
      *                     and velocities).
      * @throws LockedException if estimator is currently running.
      */
     @Override
     public void setMeasurements(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> 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 MagnetometerCalibratorMeasurementType getMeasurementType() {
         return MagnetometerCalibratorMeasurementType.STANDARD_DEVIATION_FRAME_BODY_MAGNETIC_FLUX_DENSITY;
     }
 
     /**
      * 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,
      * gyroscope and magnetometer.
      * When enabled, this eliminates 3 variables from Mm (soft-iron) matrix.
      *
      * @return true if z-axis is assumed to be common for accelerometer,
      * gyroscope and magnetometer, 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 Mm matrix.
      *
      * @param commonAxisUsed true if z-axis is assumed to be common for
      *                       accelerometer, gyroscope and magnetometer, false
      *                       otherwise.
      * @throws LockedException if estimator 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 calibrator.
      *
      * @return listener to handle events raised by this calibrator.
      */
     public RobustKnownFrameMagnetometerCalibratorListener getListener() {
         return listener;
     }
 
     /**
      * Sets listener to handle events raised by this calibrator.
      *
      * @param listener listener to handle events raised by this calibrator.
      * @throws LockedException if calibrator is currently running.
      */
     public void setListener(
             final RobustKnownFrameMagnetometerCalibratorListener 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 the estimator.
      *
      * @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 no.
      *
      * @return true if calibrator is running, false otherwise.
      */
     @Override
     public boolean isRunning() {
         return running;
     }
 
     /**
      * Gets Earth's magnetic model.
      *
      * @return Earth's magnetic model or null if not provided.
      */
     public WorldMagneticModel getMagneticModel() {
         return magneticModel;
     }
 
     /**
      * Sets Earth's magnetic model.
      *
      * @param magneticModel Earth's magnetic model to be set.
      * @throws LockedException if calibrator is currently running.
      */
     public void setMagneticModel(final WorldMagneticModel magneticModel) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.magneticModel = magneticModel;
     }
 
     /**
      * 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 magnetometer
      * hard-iron biases expressed in Teslas (T).
      *
      * @return array containing x,y,z components of estimated magnetometer
      * hard-iron biases.
      */
     @Override
     public double[] getEstimatedHardIron() {
         return estimatedHardIron;
     }
 
     /**
      * Gets array containing x,y,z components of estimated magnetometer
      * hard-iron biases expressed in Teslas (T).
      *
      * @param result instance where estimated magnetometer biases will be
      *               stored.
      * @return true if result instance was updated, false otherwise (when
      * estimation is not yet available).
      */
     @Override
     public boolean getEstimatedHardIron(final double[] result) {
         if (estimatedHardIron != null) {
             System.arraycopy(estimatedHardIron, 0, result, 0, estimatedHardIron.length);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets column matrix containing x,y,z components of estimated
      * magnetometer hard-iron biases expressed in Teslas (T).
      *
      * @return column matrix containing x,y,z components of estimated
      * magnetometer hard-iron biases.
      */
     @Override
     public Matrix getEstimatedHardIronAsMatrix() {
         return estimatedHardIron != null ? Matrix.newFromArray(estimatedHardIron) : null;
     }
 
     /**
      * Gets column matrix containing x,y,z components of estimated
      * magnetometer hard-iron biases expressed in Teslas (T).
      *
      * @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 getEstimatedHardIronAsMatrix(final Matrix result) throws WrongSizeException {
         if (estimatedHardIron != null) {
             result.fromArray(estimatedHardIron);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets x coordinate of estimated magnetometer bias expressed in
      * Teslas (T).
      *
      * @return x coordinate of estimated magnetometer bias or null if not
      * available.
      */
     @Override
     public Double getEstimatedHardIronX() {
         return estimatedHardIron != null ? estimatedHardIron[0] : null;
     }
 
     /**
      * Gets y coordinate of estimated magnetometer bias expressed in
      * Teslas (T).
      *
      * @return y coordinate of estimated magnetometer bias or null if not
      * available.
      */
     @Override
     public Double getEstimatedHardIronY() {
         return estimatedHardIron != null ? estimatedHardIron[1] : null;
     }
 
     /**
      * Gets z coordinate of estimated magnetometer bias expressed in
      * Teslas (T).
      *
      * @return z coordinate of estimated magnetometer bias or null if not
      * available.
      */
     @Override
     public Double getEstimatedHardIronZ() {
         return estimatedHardIron != null ? estimatedHardIron[2] : null;
     }
 
     /**
      * Gets x coordinate of estimated magnetometer bias.
      *
      * @return x coordinate of estimated magnetometer bias.
      */
     @Override
     public MagneticFluxDensity getEstimatedHardIronXAsMagneticFluxDensity() {
         return estimatedHardIron != null
                 ? new MagneticFluxDensity(estimatedHardIron[0], MagneticFluxDensityUnit.TESLA) : null;
     }
 
     /**
      * Gets x coordinate of estimated magnetometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if estimated magnetometer bias is available, false otherwise.
      */
     @Override
     public boolean getEstimatedHardIronXAsMagneticFluxDensity(final MagneticFluxDensity result) {
         if (estimatedHardIron != null) {
             result.setValue(estimatedHardIron[0]);
             result.setUnit(MagneticFluxDensityUnit.TESLA);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets y coordinate of estimated magnetometer bias.
      *
      * @return y coordinate of estimated magnetometer bias.
      */
     @Override
     public MagneticFluxDensity getEstimatedHardIronYAsMagneticFluxDensity() {
         return estimatedHardIron != null
                 ? new MagneticFluxDensity(estimatedHardIron[1], MagneticFluxDensityUnit.TESLA) : null;
     }
 
     /**
      * Gets y coordinate of estimated magnetometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if estimated magnetometer bias is available, false otherwise.
      */
     @Override
     public boolean getEstimatedHardIronYAsMagneticFluxDensity(final MagneticFluxDensity result) {
         if (estimatedHardIron != null) {
             result.setValue(estimatedHardIron[1]);
             result.setUnit(MagneticFluxDensityUnit.TESLA);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets z coordinate of estimated magnetometer bias.
      *
      * @return z coordinate of estimated magnetometer bias.
      */
     @Override
     public MagneticFluxDensity getEstimatedHardIronZAsMagneticFluxDensity() {
         return estimatedHardIron != null
                 ? new MagneticFluxDensity(estimatedHardIron[2], MagneticFluxDensityUnit.TESLA) : null;
     }
 
     /**
      * Gets z coordinate of estimated magnetometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if estimated magnetometer bias is available, false otherwise.
      */
     @Override
     public boolean getEstimatedHardIronZAsMagneticFluxDensity(final MagneticFluxDensity result) {
         if (estimatedHardIron != null) {
             result.setValue(estimatedHardIron[2]);
             result.setUnit(MagneticFluxDensityUnit.TESLA);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets estimated magnetometer bias.
      *
      * @return estimated magnetometer bias or null if not available.
      */
     @Override
     public MagneticFluxDensityTriad getEstimatedHardIronAsTriad() {
         return estimatedHardIron != null
                 ? new MagneticFluxDensityTriad(MagneticFluxDensityUnit.TESLA,
                 estimatedHardIron[0], estimatedHardIron[1], estimatedHardIron[2]) : null;
     }
 
     /**
      * Gets estimated magnetometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if estimated magnetometer bias is available and result was
      * modified, false otherwise.
      */
     @Override
     public boolean getEstimatedHardIronAsTriad(final MagneticFluxDensityTriad result) {
         if (estimatedHardIron != null) {
             result.setValueCoordinatesAndUnit(
                     estimatedHardIron[0], estimatedHardIron[1], estimatedHardIron[2], MagneticFluxDensityUnit.TESLA);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets estimated magnetometer soft-iron matrix containing scale factors
      * and cross coupling errors.
      * This is the product of matrix Tm containing cross coupling errors and Km
      * containing scaling factors.
      * So tat:
      * <pre>
      *     Mm = [sx    mxy  mxz] = Tm*Km
      *          [myx   sy   myz]
      *          [mzx   mzy  sz ]
      * </pre>
      * Where:
      * <pre>
      *     Km = [sx 0   0 ]
      *          [0  sy  0 ]
      *          [0  0   sz]
      * </pre>
      * and
      * <pre>
      *     Tm = [1          -alphaXy    alphaXz ]
      *          [alphaYx    1           -alphaYz]
      *          [-alphaZx   alphaZy     1       ]
      * </pre>
      * Hence:
      * <pre>
      *     Mm = [sx    mxy  mxz] = Tm*Km =  [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 Mm matrix
      * becomes upper diagonal:
      * <pre>
      *     Mm = [sx    mxy  mxz]
      *          [0     sy   myz]
      *          [0     0    sz ]
      * </pre>
      * Values of this matrix are unit-less.
      *
      * @return estimated magnetometer soft-iron scale factors and cross coupling errors,
      * or null if not available.
      */
     @Override
     public Matrix getEstimatedMm() {
         return estimatedMm;
     }
 
     /**
      * Gets estimated x-axis scale factor.
      *
      * @return estimated x-axis scale factor or null if not available.
      */
     @Override
     public Double getEstimatedSx() {
         return estimatedMm != null ? estimatedMm.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 estimatedMm != null ? estimatedMm.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 estimatedMm != null ? estimatedMm.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 estimatedMm != null ? estimatedMm.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 estimatedMm != null ? estimatedMm.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 estimatedMm != null ? estimatedMm.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 estimatedMm != null ? estimatedMm.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 estimatedMm != null ? estimatedMm.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 estimatedMm != null ? estimatedMm.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 mean square error respect to provided measurements.
      *
      * @return estimated mean square error respect to provided measurements.
      */
     @Override
     public double getEstimatedMse() {
         return estimatedMse;
     }
 
     /**
      * 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 covariance matrix for estimated calibration parameters.
      * 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.
      *
      * @return estimated covariance matrix for estimated calibration parameters.
      */
     @Override
     public Matrix getEstimatedCovariance() {
         return estimatedCovariance;
     }
 
     /**
      * Gets variance of estimated x coordinate of magnetometer bias expressed in
      * squared Teslas (T^2).
      *
      * @return variance of estimated x coordinate of magnetometer bias or null if
      * not available.
      */
     public Double getEstimatedHardIronXVariance() {
         return estimatedCovariance != null ? estimatedCovariance.getElementAt(0, 0) : null;
     }
 
     /**
      * Gets standard deviation of estimated x coordinate of magnetometer bias
      * expressed in Teslas (T).
      *
      * @return standard deviation of estimated x coordinate of magnetometer bias
      * or null if not available.
      */
     public Double getEstimatedHardIronXStandardDeviation() {
         final var variance = getEstimatedHardIronXVariance();
         return variance != null ? Math.sqrt(variance) : null;
     }
 
     /**
      * Gets standard deviation of estimated x coordinate of magnetometer bias.
      *
      * @return standard deviation of estimated x coordinate of magnetometer bias
      * or null if not available.
      */
     public MagneticFluxDensity getEstimatedHardIronXStandardDeviationAsMagneticFluxDensity() {
         return estimatedCovariance != null
                 ? new MagneticFluxDensity(getEstimatedHardIronXStandardDeviation(), MagneticFluxDensityUnit.TESLA)
                 : null;
     }
 
     /**
      * Gets standard deviation of estimated x coordinate of magnetometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if standard deviation of estimated x coordinate of
      * magnetometer bias is available, false otherwise.
      */
     public boolean getEstimatedHardIronXStandardDeviationAsMagneticFluxDensity(final MagneticFluxDensity result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedHardIronXStandardDeviation());
             result.setUnit(MagneticFluxDensityUnit.TESLA);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets variance of estimated y coordinate of magnetometer bias expressed in
      * squared Teslas (T^2).
      *
      * @return variance of estimated y coordinate of magnetometer bias or null if
      * not available.
      */
     public Double getEstimatedHardIronYVariance() {
         return estimatedCovariance != null ? estimatedCovariance.getElementAt(1, 1) : null;
     }
 
     /**
      * Gets standard deviation of estimated y coordinate of magnetometer bias
      * expressed in Teslas (T).
      *
      * @return standard deviation of estimated y coordinate of magnetometer bias
      * or null if not available.
      */
     public Double getEstimatedHardIronYStandardDeviation() {
         final var variance = getEstimatedHardIronYVariance();
         return variance != null ? Math.sqrt(variance) : null;
     }
 
     /**
      * Gets standard deviation of estimated y coordinate of magnetometer bias.
      *
      * @return standard deviation of estimated y coordinate of magnetometer bias
      * or null if not available.
      */
     public MagneticFluxDensity getEstimatedHardIronYStandardDeviationAsMagneticFluxDensity() {
         return estimatedCovariance != null
                 ? new MagneticFluxDensity(getEstimatedHardIronYStandardDeviation(), MagneticFluxDensityUnit.TESLA)
                 : null;
     }
 
     /**
      * Gets standard deviation of estimated y coordinate of magnetometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if standard deviation of estimated y coordinate of
      * magnetometer bias is available, false otherwise.
      */
     public boolean getEstimatedHardIronYStandardDeviationAsMagneticFluxDensity(final MagneticFluxDensity result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedHardIronYStandardDeviation());
             result.setUnit(MagneticFluxDensityUnit.TESLA);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets variance of estimated z coordinate of magnetometer bias expressed in
      * squared Teslas (T^2).
      *
      * @return variance of estimated z coordinate of magnetometer bias or null if
      * not available.
      */
     public Double getEstimatedHardIronZVariance() {
         return estimatedCovariance != null ? estimatedCovariance.getElementAt(2, 2) : null;
     }
 
     /**
      * Gets standard deviation of estimated z coordinate of magnetometer bias
      * expressed in Teslas (T).
      *
      * @return standard deviation of estimated z coordinate of magnetometer bias
      * or null if not available.
      */
     public Double getEstimatedHardIronZStandardDeviation() {
         final var variance = getEstimatedHardIronZVariance();
         return variance != null ? Math.sqrt(variance) : null;
     }
 
     /**
      * Gets standard deviation of estimated z coordinate of magnetometer bias.
      *
      * @return standard deviation of estimated z coordinate of magnetometer bias
      * or null if not available.
      */
     public MagneticFluxDensity getEstimatedHardIronZStandardDeviationAsMagneticFluxDensity() {
         return estimatedCovariance != null
                 ? new MagneticFluxDensity(getEstimatedHardIronZStandardDeviation(), MagneticFluxDensityUnit.TESLA)
                 : null;
     }
 
     /**
      * Gets standard deviation of estimated z coordinate of magnetometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if standard deviation of estimated z coordinate of
      * magnetometer bias is available, false otherwise.
      */
     public boolean getEstimatedHardIronZStandardDeviationAsMagneticFluxDensity(final MagneticFluxDensity result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedHardIronZStandardDeviation());
             result.setUnit(MagneticFluxDensityUnit.TESLA);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets standard deviation of estimated magnetometer bias coordinates.
      *
      * @return standard deviation of estimated magnetometer bias coordinates.
      */
     public MagneticFluxDensityTriad getEstimatedHardIronStandardDeviation() {
         return estimatedCovariance != null
                 ? new MagneticFluxDensityTriad(MagneticFluxDensityUnit.TESLA,
                 getEstimatedHardIronXStandardDeviation(),
                 getEstimatedHardIronYStandardDeviation(),
                 getEstimatedHardIronZStandardDeviation())
                 : null;
     }
 
     /**
      * Gets standard deviation of estimated magnetometer bias coordinates.
      *
      * @param result instance where result will be stored.
      * @return true if standard deviation of magnetometer bias was available,
      * false otherwise.
      */
     public boolean getEstimatedHardIronStandardDeviation(final MagneticFluxDensityTriad result) {
         if (estimatedCovariance != null) {
             result.setValueCoordinatesAndUnit(
                     getEstimatedHardIronXStandardDeviation(),
                     getEstimatedHardIronYStandardDeviation(),
                     getEstimatedHardIronZStandardDeviation(),
                     MagneticFluxDensityUnit.TESLA);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets average of estimated standard deviation of magnetometer bias coordinates
      * expressed in Teslas (T).
      *
      * @return average of estimated standard deviation of magnetometer bias coordinates,
      * or null if not available.
      */
     public Double getEstimatedHardIronStandardDeviationAverage() {
         return estimatedCovariance != null
                 ? (getEstimatedHardIronXStandardDeviation() + getEstimatedHardIronYStandardDeviation()
                 + getEstimatedHardIronZStandardDeviation()) / 3.0
                 : null;
     }
 
     /**
      * Gets average of estimated standard deviation of magnetometer bias coordinates.
      *
      * @return average of estimated standard deviation of magnetometer bias coordinates,
      * or null if not available.
      */
     public MagneticFluxDensity getEstimatedHardIronStandardDeviationAverageAsMagneticFluxDensity() {
         return estimatedCovariance != null
                 ? new MagneticFluxDensity(getEstimatedHardIronStandardDeviationAverage(),
                 MagneticFluxDensityUnit.TESLA)
                 : null;
     }
 
     /**
      * Gets average of estimated standard deviation of magnetometer bias coordinates.
      *
      * @param result instance where result will be stored.
      * @return true if average of estimated standard deviation of magnetometer bias is available,
      * false otherwise.
      */
     public boolean getEstimatedHardIronStandardDeviationAverageAsMagneticFluxDensity(
             final MagneticFluxDensity result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedHardIronStandardDeviationAverage());
             result.setUnit(MagneticFluxDensityUnit.TESLA);
             return true;
         } else {
             return false;
         }
     }
 
     /**
      * Gets norm of estimated standard deviation of magnetometer bias expressed in
      * Teslas (T).
      *
      * @return norm of estimated standard deviation of magnetometer bias or null
      * if not available.
      */
     public Double getEstimatedHardIronStandardDeviationNorm() {
         return estimatedCovariance != null
                 ? Math.sqrt(getEstimatedHardIronXVariance()
                 + getEstimatedHardIronYVariance()
                 + getEstimatedHardIronZVariance())
                 : null;
     }
 
     /**
      * Gets norm of estimated standard deviation of magnetometer bias.
      *
      * @return norm of estimated standard deviation of magnetometer bias or null
      * if not available.
      */
     public MagneticFluxDensity getEstimatedHardIronStandardDeviationNormAsMagneticFluxDensity() {
         return estimatedCovariance != null
                 ? new MagneticFluxDensity(getEstimatedHardIronStandardDeviationNorm(), MagneticFluxDensityUnit.TESLA)
                 : null;
     }
 
     /**
      * Gets norm of estimated standard deviation of magnetometer bias.
      *
      * @param result instance where result will be stored.
      * @return true if norm of estimated standard deviation of magnetometer bias
      * is available, false otherwise.
      */
     public boolean getEstimatedHardIronStandardDeviationNormAsMagneticFluxDensity(final MagneticFluxDensity result) {
         if (estimatedCovariance != null) {
             result.setValue(getEstimatedHardIronStandardDeviationNorm());
             result.setUnit(MagneticFluxDensityUnit.TESLA);
             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 known frame magnetometer calibrator.
      *
      * @param method robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator();
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator();
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator();
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator();
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator();
         };
     }
 
     /**
      * Creates a robust known frame magnetometer 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 known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final RobustKnownFrameMagnetometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(listener);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(listener);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(listener);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(listener);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(listener);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator.
      *
      * @param measurements list of body magnetic flux density measurements with standard
      *                     deviations taken at different frames (positions and
      *                     orientations).
      * @param method       robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(measurements);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(measurements);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(measurements);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(measurements);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(measurements);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator.
      *
      * @param measurements list of body magnetic flux density measurements with standard
      *                     deviations taken at different frames (positions and
      *                     orientations).
      * @param listener     listener to handle events raised by this calibrator.
      * @param method       robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final RobustKnownFrameMagnetometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(measurements, listener);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(measurements, listener);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(measurements, listener);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(measurements, listener);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(measurements, listener);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param method         robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final boolean commonAxisUsed, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(commonAxisUsed);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(commonAxisUsed);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      * @param method         robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final boolean commonAxisUsed, final RobustKnownFrameMagnetometerCalibratorListener listener,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed, listener);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(commonAxisUsed, listener);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed, listener);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed, listener);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(commonAxisUsed, listener);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator.
      *
      * @param measurements   list of body magnetic flux density measurements with standard
      *                       deviations taken at different frames (positions and
      *                       orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param method         robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator.
      *
      * @param measurements   list of body magnetic flux density measurements with standard
      *                       deviations taken at different frames (positions and
      *                       orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      * @param method         robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final RobustKnownFrameMagnetometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed, listener);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed, listener);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed, listener);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed, listener);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed, listener);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer 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 known frame magnetometer calibrator.
      * @throws IllegalArgumentException if provided quality scores length
      *                                  is smaller than 4 samples.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final double[] qualityScores, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator();
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator();
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator();
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(qualityScores);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(qualityScores);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer 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 known frame magnetometer calibrator.
      * @throws IllegalArgumentException if provided quality scores length
      *                                  is smaller than 4 samples.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final double[] qualityScores, final RobustKnownFrameMagnetometerCalibratorListener listener,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(listener);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(listener);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(listener);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(qualityScores, listener);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(qualityScores, listener);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer 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 magnetic flux density measurements with standard
      *                      deviations taken at different frames (positions and
      *                      orientations).
      * @param method        robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      * @throws IllegalArgumentException if provided quality scores length
      *                                  is smaller than 4 samples.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(measurements);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(measurements);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(measurements);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(qualityScores, measurements);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(qualityScores, measurements);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer 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 magnetic flux density measurements with standard
      *                      deviations taken at different frames (positions and
      *                      orientations).
      * @param listener      listener to handle events raised by this calibrator.
      * @param method        robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      * @throws IllegalArgumentException if provided quality scores length
      *                                  is smaller than 4 samples.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final RobustKnownFrameMagnetometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(measurements, listener);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(measurements, listener);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(measurements, listener);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(qualityScores, measurements, listener);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(qualityScores, measurements, listener);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer 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 the accelerometer, gyroscope and magnetometer.
      * @param method         robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      * @throws IllegalArgumentException if provided quality scores length
      *                                  is smaller than 4 samples.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final double[] qualityScores, final boolean commonAxisUsed, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(commonAxisUsed);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(qualityScores, commonAxisUsed);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(qualityScores, commonAxisUsed);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer 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 the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      * @param method         robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      * @throws IllegalArgumentException if provided quality scores length
      *                                  is smaller than 4 samples.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final double[] qualityScores, final boolean commonAxisUsed,
             final RobustKnownFrameMagnetometerCalibratorListener listener, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed, listener);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(commonAxisUsed, listener);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(commonAxisUsed, listener);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(qualityScores, commonAxisUsed, listener);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(qualityScores, commonAxisUsed, listener);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer 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 magnetic flux density measurements with standard
      *                       deviations taken at different frames (positions and
      *                       orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param method         robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      * @throws IllegalArgumentException if provided quality scores length
      *                                  is smaller than 4 samples.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final boolean commonAxisUsed, final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(
                     qualityScores, measurements, commonAxisUsed);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(qualityScores, measurements, commonAxisUsed);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer 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 magnetic flux density measurements with standard
      *                       deviations taken at different frames (positions and
      *                       orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      * @param method         robust estimator method.
      * @return a robust known frame magnetometer calibrator.
      * @throws IllegalArgumentException if provided quality scores length
      *                                  is smaller than 4 samples.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final double[] qualityScores, final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final boolean commonAxisUsed, final RobustKnownFrameMagnetometerCalibratorListener listener,
             final RobustEstimatorMethod method) {
         return switch (method) {
             case RANSAC -> new RANSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed, listener);
             case LMEDS -> new LMedSRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed, listener);
             case MSAC -> new MSACRobustKnownFrameMagnetometerCalibrator(measurements, commonAxisUsed, listener);
             case PROSAC -> new PROSACRobustKnownFrameMagnetometerCalibrator(qualityScores, measurements, commonAxisUsed,
                     listener);
             default -> new PROMedSRobustKnownFrameMagnetometerCalibrator(qualityScores, measurements, commonAxisUsed,
                     listener);
         };
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator using default robust method.
      *
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create() {
         return create(DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust known frame magnetometer 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 known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final RobustKnownFrameMagnetometerCalibratorListener listener) {
         return create(listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator using default robust method.
      *
      * @param measurements list of body magnetic flux density measurements with standard
      *                     deviations taken at different frames (positions and
      *                     orientations).
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements) {
         return create(measurements, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator using default robust method.
      *
      * @param measurements list of body magnetic flux density measurements with standard
      *                     deviations taken at different frames (positions and
      *                     orientations).
      * @param listener     listener to handle events raised by this calibrator.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final RobustKnownFrameMagnetometerCalibratorListener listener) {
         return create(measurements, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator using default robust method.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(final boolean commonAxisUsed) {
         return create(commonAxisUsed, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator using default robust method.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final boolean commonAxisUsed, final RobustKnownFrameMagnetometerCalibratorListener listener) {
         return create(commonAxisUsed, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator using default robust method.
      *
      * @param measurements   list of body magnetic flux density measurements with standard
      *                       deviations taken at different frames (positions and
      *                       orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed) {
         return create(measurements, commonAxisUsed, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Creates a robust known frame magnetometer calibrator using default robust method.
      *
      * @param measurements   list of body magnetic flux density measurements with standard
      *                       deviations taken at different frames (positions and
      *                       orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      * @return a robust known frame magnetometer calibrator.
      */
     public static RobustKnownFrameMagnetometerCalibrator create(
             final List<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final RobustKnownFrameMagnetometerCalibratorListener listener) {
         return create(measurements, commonAxisUsed, listener, DEFAULT_ROBUST_METHOD);
     }
 
     /**
      * Setups World Magnetic Model estimator.
      *
      * @throws IOException if model cannot be loaded.
      */
     protected void setupWmmEstimator() throws IOException {
         if (magneticModel != null) {
             wmmEstimator = new WMMEarthMagneticFluxDensityEstimator(magneticModel);
         } else {
             wmmEstimator = new WMMEarthMagneticFluxDensityEstimator();
         }
     }
 
     /**
      * 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 StandardDeviationFrameBodyMagneticFluxDensity measurement,
             final PreliminaryResult preliminaryResult) {
         // The magnetometer model is:
         // mBmeas = ba + (I + Mm) * mBtrue
 
         // Hence:
         // [mBmeasx] = [bx] + ( [1  0   0] + [sx    mxy mxz]) [mBtruex]
         // [mBmeasy] = [by]     [0  1   0]   [myx   sy  myz]  [mBtruey]
         // [mBmeasz] = [bz]     [0  0   1]   [mzx   mzy sz ]  [mBtruez]
 
         final var measuredMagneticFluxDensity = measurement.getMagneticFluxDensity();
         final var ecefFrame = measurement.getFrame();
 
         final var nedFrame = ECEFtoNEDFrameConverter.convertECEFtoNEDAndReturnNew(ecefFrame);
         final var year = measurement.getYear();
 
         final var latitude = nedFrame.getLatitude();
         final var longitude = nedFrame.getLongitude();
         final var height = nedFrame.getHeight();
 
         final var earthB = wmmEstimator.estimate(latitude, longitude, height, year);
 
         final var cbn = new CoordinateTransformation(FrameType.BODY_FRAME, FrameType.LOCAL_NAVIGATION_FRAME);
         final var cnb = new CoordinateTransformation(FrameType.LOCAL_NAVIGATION_FRAME, FrameType.BODY_FRAME);
 
         nedFrame.getCoordinateTransformation(cbn);
         cbn.inverse(cnb);
 
         final var expectedMagneticFluxDensity = BodyMagneticFluxDensityEstimator.estimate(earthB, cnb);
 
         final var bMeasX1 = measuredMagneticFluxDensity.getBx();
         final var bMeasY1 = measuredMagneticFluxDensity.getBy();
         final var bMeasZ1 = measuredMagneticFluxDensity.getBz();
 
         final var bTrueX = expectedMagneticFluxDensity.getBx();
         final var bTrueY = expectedMagneticFluxDensity.getBy();
         final var bTrueZ = expectedMagneticFluxDensity.getBz();
 
         final var b = preliminaryResult.estimatedHardIron;
         final var bx = b[0];
         final var by = b[1];
         final var bz = b[2];
 
         final var mm = preliminaryResult.estimatedMm;
 
         try {
             final var m = Matrix.identity(BodyKinematics.COMPONENTS, BodyKinematics.COMPONENTS);
             m.add(mm);
 
             final var btrue = new Matrix(BodyKinematics.COMPONENTS, 1);
             btrue.setElementAtIndex(0, bTrueX);
             btrue.setElementAtIndex(1, bTrueY);
             btrue.setElementAtIndex(2, bTrueZ);
 
             m.multiply(btrue);
 
             final var bMeasX2 = bx + m.getElementAtIndex(0);
             final var bMeasY2 = by + m.getElementAtIndex(1);
             final var bMeasZ2 = bz + m.getElementAtIndex(2);
 
             final var diffX = bMeasX2 - bMeasX1;
             final var diffY = bMeasY2 - bMeasY1;
             final var diffZ = bMeasZ2 - bMeasZ1;
 
             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<StandardDeviationFrameBodyMagneticFluxDensity>();
 
         for (final var samplesIndex : samplesIndices) {
             meas.add(this.measurements.get(samplesIndex));
         }
 
         try {
             final var result = new PreliminaryResult();
             result.estimatedHardIron = getInitialHardIron();
             result.estimatedMm = getInitialMm();
 
             if (useLinearCalibrator) {
                 linearCalibrator.setCommonAxisUsed(commonAxisUsed);
                 linearCalibrator.setMeasurements(meas);
                 linearCalibrator.calibrate();
 
                 linearCalibrator.getEstimatedHardIron(result.estimatedHardIron);
                 result.estimatedMm = linearCalibrator.getEstimatedMm();
             }
 
             if (refinePreliminarySolutions) {
                 nonLinearCalibrator.setInitialHardIron(result.estimatedHardIron);
                 nonLinearCalibrator.setInitialMm(result.estimatedMm);
                 nonLinearCalibrator.setCommonAxisUsed(commonAxisUsed);
                 nonLinearCalibrator.setMeasurements(meas);
                 nonLinearCalibrator.calibrate();
 
                 nonLinearCalibrator.getEstimatedHardIron(result.estimatedHardIron);
                 result.estimatedMm = nonLinearCalibrator.getEstimatedMm();
 
                 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<StandardDeviationFrameBodyMagneticFluxDensity>();
             for (var i = 0; i < nSamples; i++) {
                 if (inliers.get(i)) {
                     // sample is inlier
                     inlierMeasurements.add(measurements.get(i));
                 }
             }
 
             try {
                 nonLinearCalibrator.setInitialHardIron(preliminaryResult.estimatedHardIron);
                 nonLinearCalibrator.setInitialMm(preliminaryResult.estimatedMm);
                 nonLinearCalibrator.setCommonAxisUsed(commonAxisUsed);
                 nonLinearCalibrator.setMeasurements(inlierMeasurements);
                 nonLinearCalibrator.calibrate();
 
                 estimatedHardIron = nonLinearCalibrator.getEstimatedHardIron();
                 estimatedMm = nonLinearCalibrator.getEstimatedMm();
                 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;
                 estimatedHardIron = preliminaryResult.estimatedHardIron;
                 estimatedMm = preliminaryResult.estimatedMm;
                 estimatedMse = preliminaryResult.estimatedMse;
                 estimatedChiSq = preliminaryResult.estimatedChiSq;
                 estimatedChiSqDegreesOfFreedom = preliminaryResult.estimatedChiSqDegreesOfFreedom;
                 estimatedReducedChiSq = preliminaryResult.estimatedReducedChiSq;
                 estimatedP = preliminaryResult.estimatedP;
                 estimatedQ = preliminaryResult.estimatedQ;
             }
         } else {
             estimatedCovariance = preliminaryResult.covariance;
             estimatedHardIron = preliminaryResult.estimatedHardIron;
             estimatedMm = preliminaryResult.estimatedMm;
             estimatedMse = preliminaryResult.estimatedMse;
             estimatedChiSq = preliminaryResult.estimatedChiSq;
             estimatedChiSqDegreesOfFreedom = preliminaryResult.estimatedChiSqDegreesOfFreedom;
             estimatedReducedChiSq = preliminaryResult.estimatedReducedChiSq;
             estimatedP = preliminaryResult.estimatedP;
             estimatedQ = preliminaryResult.estimatedQ;
         }
     }
 
     /**
      * Converts magnetic flux density value and unit to Teslas.
      *
      * @param value magnetic flux density value.
      * @param unit  unit of magnetic flux density value.
      * @return converted value.
      */
     private static double convertMagneticFluxDensity(final double value, final MagneticFluxDensityUnit unit) {
         return MagneticFluxDensityConverter.convert(value, unit, MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Converts magnetic flux density instance to Teslas.
      *
      * @param magneticFluxDensity magnetic flux density instance to be converted.
      * @return converted value.
      */
     private static double convertMagneticFluxDensity(final MagneticFluxDensity magneticFluxDensity) {
         return convertMagneticFluxDensity(magneticFluxDensity.getValue().doubleValue(), magneticFluxDensity.getUnit());
     }
 
     /**
      * Internal class containing estimated preliminary result.
      */
     protected static class PreliminaryResult {
         /**
          * Estimated magnetometer hard-iron biases for each magnetometer axis
          * expressed in Teslas (T).
          */
         private double[] estimatedHardIron;
 
         /**
          * Estimated magnetometer soft-iron matrix containing scale factors
          * and cross coupling errors.
          * This is the product of matrix Tm containing cross coupling errors and Km
          * containing scaling factors.
          * So tat:
          * <pre>
          *     Mm = [sx    mxy  mxz] = Tm*Km
          *          [myx   sy   myz]
          *          [mzx   mzy  sz ]
          * </pre>
          * Where:
          * <pre>
          *     Km = [sx 0   0 ]
          *          [0  sy  0 ]
          *          [0  0   sz]
          * </pre>
          * and
          * <pre>
          *     Tm = [1          -alphaXy    alphaXz ]
          *          [alphaYx    1           -alphaYz]
          *          [-alphaZx   alphaZy     1       ]
          * </pre>
          * Hence:
          * <pre>
          *     Mm = [sx    mxy  mxz] = Tm*Km =  [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 Mm matrix
          * becomes upper diagonal:
          * <pre>
          *     Mm = [sx    mxy  mxz]
          *          [0     sy   myz]
          *          [0     0    sz ]
          * </pre>
          * Values of this matrix are unit-less.
          */
         private Matrix estimatedMm;
 
         /**
          * Estimated covariance matrix.
          */
         private Matrix covariance;
 
         /**
          * Estimated Mean Squared Error (MSE).
          */
         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;
     }
 }