SMOOTHING TECHNIQUE USING FOURIER-TRANSFORMS APPLIED TO STEREOMETRIC DATA OBTAINED FROM OPTOELECTRONIC RECORDINGS OF HUMAN GAIT

Stereometric recording on a VICON(TM) optoelectronic system of a contr olled experimental signal in which the system is used in conditions cl ose to the real clinical circumstances of a study on gait indicated th e presence of non-stochastic and non-random errors during the spatial localization of markers. This observation contradicts a data smoothing technique using repeated recordings and the computation of a mean sig nal. The experimental signal corresponded to sinusoidal angular variat ions of +/- 1 degrees, calculated from the spatial localizations of 4 markers with a sampling frequency of 50 Hz. The mean error for the the oretical signal was 0.30 degrees, with the maximum reaching 0.91 degre es. Filtration by Fourier transforms with a cut-off frequency of 10 Hz made it possible to totally eliminate the raw data noise and to reduc e the signal error to +/- 0.01 degrees. With this smoothing technique, variations of the signal velocity and acceleration that were very clo se to the theoretical values were calculated.