The effect of camera location on observation-based posture estimation

This study used the observation-based method showing images on computer to evaluate angle estimation errors of 8 body segments in 3 motion planes at up to 28 segment angles and 5 camera locations with respect to goniometric measurements. Thirty observers participated in evaluating segment angles. Forearm (9.98) and thigh (9.58) had smaller errors than hand (14.08) and foot had the smallest error (8.78) due to its narrow range of motion (ROM). Errors were small with camera locations perpendicular to motions in the planes, such as 908 camera location for the flexion and extension of arm (6.38), forearm (7.98), thigh (6.58), and leg (8.18) in the sagittal plane. Segments had small errors of 3.18, 4.68, and 3.88 at segment angles of 7908, 08 and 908, respectively. Care should be taken when estimating angles by the observation-based method for a specific segment motion and viewing direction is suggested to be perpendicular to the motion plane.