Dynamic Control of Captured Motions to Verify New Constraints

Simulating realistic human-like figures is still a challenging task when dynamics is involved. For example, making a virtual human jump to a given position requires to control the forces involved in take-off in order to reach a given velocity vector at the beginning of the aerial phase. Several problems are addressed in this paper in order to modify a captured motion while accounting from dynamics. The method exploits a point mass approximation of the body for the Inverse Dynamics stage during the contact phase and later to optimize new trajectories. First, accurate body segment masses are required to have access to external forces thanks to inverse dynamics. Second, those forces have to be adapted to make the resulting center of mass trajectory verify new constraints (such as reaching a given point at a given time). This paper also proposes a new formalism to encode force depending on time in contact phases (called impulse). Whereas classical biomechanical analyzes focus only on the peak of forces and on the contact phase duration, our formalism provides new data to characterize the shape of an impulse.