an optical system tracks the motion of objects , including the human body or portions thereof using a plurality of three - dimensional active markers based upon triangulation from data read via multiple linear ccds through cylindrical lenses . each marker is lit in sequence so that it is in sync with a frame capture using the imaging system positioned and oriented so as to provide a basis for computing three - dimensional location . in the preferred embodiment , the imaging system detects an infrared signal which is sent out by the tag controller as part of the tag / marker illumination sequence at the beginning of the first tag position capture time . the controller then traverses through the tags in time sync with each imaging system frame capture cycle . thus , only one unique tag will be lit during each image capture of the cameras , thereby simplifying identification . using linear ccd sensors , the frame time is very short , allowing very many markers to be sampled and located sequentially in real time .