calibrationExample.m

%% Example of accelerometer calibration and test with data
% This shows an example of accelerometer calibration using the method
% described by Gietzelt, M., Wolf, K. H., Marschollek, M., & Haux, R. (2013). 
% Performance comparison of accelerometer calibration algorithms based 
% on 3D-ellipsoid fitting methods. Computer Methods and Programs in 
% Biomedicine, 111(1), 62-71. http://doi.org/10.1016/j.cmpb.2013.03.006

%% Loading and view the calibration data
%Load the calibration data. This was recorded making slow movements in the
%accelerometer in such way the gravity vector forms a sphere.

load calib_acc_01.mat

accXcalib = double(Respiratory_Sensor_Port_COM3_Canal_0_g_Amplitude);
accYcalib = double(Respiratory_Sensor_Port_COM3_Canal_1_g_Amplitude);
accZcalib = double(Respiratory_Sensor_Port_COM3_Canal_2_g_Amplitude);

%Plot the data so you can see the movement made.

plot3(accXcalib, accYcalib, accZcalib);

%% Calculate the accelerometer calibration parameters

[ offset, scale, radius ] = calibrateAccelerometer(accXcalib, accYcalib, accZcalib)


%% Loading a test accelerometer signal

%Load the test signal. This signal contains the accelerometer fixed in 12
%different positions.

%Concatenate the data
accX = [];
accY = [];
accZ = [];

for n=1:12

    load(['fix_acc_01_' num2str(n) '.mat'])

    eval(['accX = [accX Respiratory_Sensor_Port_COM3_Canal_0_g_Amplitude];']);
    eval(['accY = [accY Respiratory_Sensor_Port_COM3_Canal_1_g_Amplitude];']);
    eval(['accZ = [accZ Respiratory_Sensor_Port_COM3_Canal_2_g_Amplitude];']);

end

%Plot the data so you can see the test points on the sphere.

plot3(accX, accY, accZ, 'x');

%% Calculate the norm of the acceleration before the calibration

%Norm of the acceleration before the calibration
modBeforeCalibration = sqrt(accX.^2 + accY.^2 + accZ.^2);

%The histogram of the norm before the calibration.
hist(modBeforeCalibration,20);
title(['Before calibration']);
xlim([0.8 1.2]);

%% Applying the calibration factors

%Apply the calibration factors
[ calibAccX, calibAccY, calibAccZ ] = applyCalibrationFactor( accX, accY, accZ, offset, scale );


%% Calculate the norm after the calibration
modAfterCalibration = sqrt(calibAccX.^2 + calibAccY.^2 + calibAccZ.^2);

%Comparing the histogram before and after the calibration.
subplot(2, 1, 1);
hist(modBeforeCalibration,20);
title(['Before calibration']);
xlim([0.8 1.2]);
xlabel('Acceleration (g)');
subplot(2, 1, 2);
hist(modAfterCalibration,20);
title('After calibration');
xlim([0.8 1.2]);
xlabel('Acceleration (g)');

%% Copyright 2016 Ailton Luiz Dias Siqueira Junior.
%
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
% 
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
% 
% You should have received a copy of the GNU General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.