3D VIDEO DIGITIZING AND MOTION ANALYSIS

Abstract

Video digitizing analysis system was introduced by Shapiro et al. (1987). It was concluded that the digitizing errors are similar in magnitude to those observed in cinematographic analysis. At the Biomechanics Laboratory of the Liverpool Polytechnic we had the opportunity to create an advanced version of our previous video motion analysis system (Barton and Barton, 1990). The hardware is a Panasonic SVHS VW-SHSl video camera, a Panasonic AG-7330-E video recorder and an IBM AT compatible PC with MicroEye 2C (Digithurst) real-time Image Capture Card. The software for digitizing co-ordinates and calculating kinematic data was written in TURBO PASCAL For 3D vision usually two "synchronized" detectors (cameras) are needed, but we tried to use a method, which makes possible 3D motion analysis with only a single camera. The simplified mathematical base is the following: if it is known the original length of a body segment, and we can measure the actual length of the segment, then we can calculate the third co-ordinates of the segment's endpoints. The hardware is simplified, and that's why the operator has to take part in the digitizing procedure more activity. He has to decide, whether the third co-ordinate is positive or negative. In other words, whether the segment is orientated so that it points toward or away from the camera, which is evident for the operator, but would be an enormous task for the computer ,(Riley et al. 1978). The digitizing procedure is similar to our former system (Barton and Barton, 1988), uses mouse, shows all the time the sideview, topview and rearview of the figure during its “birth”. The motion is reconstructed in 3D, around a defined origin the motion can be rotated, magnified etc. Single points can be chosen from the 35 estimated or calculated points. We use a modified Dempster model with three trunk segments (Barton, 1984). The program calculates the trajectories, velocities of these points, of course in space, and all the projections of the physical parameters. The software is graphically orientated, but using a cursor the numerical output is available as well. The study was supported by a grant from the TEMPUS.