3D articulated models and multiview tracking with physical forces

We present a method for automatically estimating the motion of an articulat ed object filmed by two or more fixed cameras, We focus our work on the cas e where the quality of the images is poor, and where only an approximation of a geometric model of the tracked object is available. Our technique uses physical forces applied to each rigid part of a kinematic 3D model of the object we are tracking. These forces guide the minimization of the differen ces between the pose of the 3D model and the pose of the real object in the video images. We use a fast recursive algorithm to solve the dynamical equ ations of motion of any 3D articulated model. We explain the key parts of o ur algorithms: how relevant information is extracted from the images, how t he forces are created, and how the dynamical equations of motion are solved . A study of what kind of information should be extracted in the images and of when our algorithms fail is also presented. Finally we present some res ults about the tracking of a person. We also show the application of our me thod to the tracking of a hand in sequences of images, showing that the kin d of information to extract from the images depends on their quality and of the configuration of the cameras. (C) 2001 Academic Press.