Design, implementation & analysis of a low-cost, portable, medical measurement system through computer vision

Design, Implementation & Analysis of a Low-Cost, Portable, Medical Measurement System through Computer Vision G. van der Westhuizen Department of Mechanical and Mechatronic Engineering, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Thesis: MScEng (Mechatronic) March 2011 The In the Physiotherapy Division of the Faculty of Health Sciences on the Tygerberg Hospital Campus of the University of Stellenbosch, the challenge arose to develop a portable, affordable and yet accurate 3D measurement machine for the assessment of posture in school children in their classroom environment. Currently Division already uses a state-of-the-art VICON commercial medical measuring machine to measure human posture in 3D in their physiotherapy clinic, but the system is not portable and is too expensive to cart around to different places for testing. To respond to this challenge, this Master’s thesis designed and analyzed a machine and its supporting system through both research on stereo-vision methodologies and empirical appraisal in the field. In the development process, the research was required to overcome the limitations posed by small image resolutions and lens distortions that are typical of cheap cameras. The academic challenge lay in the development of an error prediction model through Jacobian derivation and Error Propagation Law, to predict uncertainties of angular measurement calculated by the system. The research culminated in a system that is comparable in accuracy to the VICON within 3 mm, and that has 1.5 mm absolute accuracy within its own system