DIRECT LINEAR TRANSFORMATION CALIBRATION TECHNIQUE OF A LOW-COST PORTABLE 3D HUMAN MOTION ANALYSIS SYSTEM
Keywords:
Camera calibration, low-cost human motion analysis system, 3-Dimensional camera capture system, gait analysisAbstract
Camera calibration is a significant part of the accuracy of three-dimensional (3D) human motion analysis systems. Gait analysis is selected as the case study for consideration to apply a low-cost three-dimensional motion capture system to evaluate gait characteristics. Kinovea (free and open source) is used to retrieve the target position in two-dimensional (2D) coordinates from two cameras and the direct linear transformation (DLT) is then utilized to determine the 3D coordinates of an object using MATLAB. Statistical analysis for the study includes (1) the mean absolute error: MAE, (2) the root mean squared error: RMSE, and (3) %RMSE. Findings indicate that the acceptable accuracy for the low-cost gait analysis system at 95% confidence level is between 1.13-1.36 mm. It shows that most of the MAE, RMSE, and %RMSE calibration values of 13 markers in the XY, YZ, and XYZ planes are within acceptable range. However, it is found that some markers in the rear plane are out of bounds. Therefore, the use of two cameras for tracking human motions may affect the accuracy of the coordinate positions in the rear plane. Test-retest reliability is estimated using intraclass correlation coefficient (ICC3, 1) stability of measurement is statistically examined with the standard error of measurement (SEM) and minimal detectable change (MDC) at the 95% confidence level. The system showed good to excellent reliability (ICC0.75) for both of kinematic gait parameters. Findings revealed that 3-D kinematic gait assessments systems using low-cost camera technology can be reliably used for human motion research and application.
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