Realtime, physics-based marker following

Abstract

Finding torques that control a physical model to follow motion capture marker data can be complicated. We present a simple method for first constraining a physical model to follow marker data using forward simulation with intuitive parametrization. Essentially, the markers attach to the model through joint constraints and drag the body into position. We then use forward simulation to compute joint torques that produce the same movement. This is accomplished by adding constraints on the relative angular velocities of the body parts to the physical model. Framing the movement in terms of constraints on the model allows us to use the Open Dynamics physics engine (ODE) to find torques that simultaneously account for joint limits, body momentum, and ground/contact constraints. Although balanced movement still requires some external stabilizing torques, these torques are generally quite small and can potentially be addressed by minor changes in foot placement. © 2012 Springer-Verlag Berlin Heidelberg.