Spatial reconstruction of the human motion based on images of a single camera

The inverse dynamic analysis procedures used in the study of the human gait require that the kinematics of the supporting biomechanical model is known beforehand. The first step to obtain the kinematic data is the reconstruct ion of human spatial motion, i.e., the evaluation of the anatomic points po sitions that enables to uniquely define the position of all anatomical segm ents. In photogrammetry, the projection of each anatomical point is describ ed by two linear equations relating its three spatial coordinates with the two coordinates of the projected point. The need for the image of two camer as arises from the fact that three equations are necessary to find the orig inal spatial position of the anatomical point. It is shown here that the ki nematic constraint equations associated with a biomechanical model can be u sed as the extra set of equations required for the reconstruction process, instead of the equations associated with the second camera. With this metho dology, the system of equations arising from the point projections and biom echanical model kinematic constraints are solved simultaneously. Since the system of equations has multiple solutions for each image, a strategy based on the minimization of the cost function associated to the smoothness of t he reconstructed motion is devised, leading to an automated computer proced ure enabling a unique reconstruction. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.