calibra_mounting

Calculates the mounting calibration frame matrix from six+ static positions using the rotational calibration method.

Syntax

Mrot = calibra_mounting(Accs, Mags, num_pos, t_movimiento, vCALIBRA, k_inicial, f_s, t_espera);

Description

Mrot = calibra_ejez(Accs, Mags, num_pos, t_movimiento, vCALIBRA, k_inicial, f_s, t_espera_calibra) the initial data come from signals from a triad of accelerometers Accs and a triad of magnetic sensors Mags, usually part of the same IMU. The IMU is left static during a time lapse (in seconds) t_espera, in six or more orientations num_pos, defined by their orientation matrix stored in vCALIBRA. The initial sample k_inicial must be provided, and the data sampling frequency f_s. The transition time between the static num_pos positions must be provided also, t_movimiento.

In the example of the figure there are 6 orientations, (a)-(f) and return to the initial (a). For each orientation we know the time it takes to reach it t_movimiento, and its description in the form of orientation matrix, in the rows of the matrix vCALIBRA, which in this case is 6x9. The initial instant k_inicial and the sampling frequency f_s are also known, the first usually known by visual inspection of the data.

Input Arguments

Accs nx3 columns matrix

Mags nx3 columns matrix

num_pos integer with the number of calibration positions

t_movimiento 1xnum_pos vector with the estimated transition time between positions

vCALIBRA num_posx9 matrix, each row being the orientation matrix corresponding to the corresponding calibration position. The orientation matrix is converted to a row vector by appending their rows : [row1 row2 row3].

k_inicial integer with the initial sample

f_s float with the sampling period

t_espera float with the static time per position (seconds)

Ouput Arguments

Mrot 3x3 orientation matrix

Examples

% Cargamos los datos de un experimento de calibracion ya conocido:
filename = 'xsens_686aa.txt';
datos_todos=cargar_datos_xsens(filename);
Error using textscan
Invalid file identifier. Use fopen to generate a valid file identifier.

Error in cargar_datos_xsens (line 54)
dataArray = textscan(fileID, formatSpec, endRow(1)-startRow(1)+1, 'Delimiter', delimiter, 'EmptyValue' ,NaN,'HeaderLines', startRow(1)-1, 'ReturnOnError', false, 'EndOfLine', '\r\n');
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
% Visualization of the need of a proper calibration: horiz accs not in zero
plot(datos_todos.Accel(1660:1700,:)); grid;
% Visualization of the data section that will be used for calibration:
plot(datos_todos.Accel(1600:5000,:)); grid;
 
% Experimental data of this specific calibration procedure:
num_posiciones=6;   % number of calibration positions
t_movimiento= [0.4 0.4 0.4 0.4 0.75 0.75]; % time taken to change position 
t_espera_calibra=2; % time at rest in each position 
% Orientation matrices of the six calibration positions:
vCALIBRA(1,:)=[ 1  0  0   0  1  0   0  0  1];
vCALIBRA(2,:)=[ 1  0  0   0  0 -1   0  1  0];
vCALIBRA(3,:)=[ 1  0  0   0 -1  0   0  0 -1];
vCALIBRA(4,:)=[ 1  0  0   0  0  1   0 -1  0];
vCALIBRA(5,:)=[ 0  0  1   0  1  0  -1  0  0];
vCALIBRA(6,:)=[ 0  0 -1   0  1  0   1  0  0];
k_inicial=2121;     % por inspeccion
f_s=120;            % muestras/s 
 
% Calibracion:
Mrot=calibra_mounting(datos_todos.Accel, datos_todos.Gyro, num_posiciones, t_movimiento,...
    vCALIBRA, k_inicial, f_s, t_espera_calibra)
 
% Use of the calibration to correct the data: 
accs_cal=(Mrot*datos_todos.Accel')';
 
% Display of already calibrated data:
plot(accs_cal(1600:5000,:)); grid;