Computer Graphics Forum, 2(4), October 1992

1

Combined Direct and Inverse Kinematic Control
for Articulated Figure Motion Editing

Ronan Boulic

Daniel Thalmann

Computer Graphics Lab
Swiss Federal Institute of Technology, Lausanne, CH1015 Switzerland
tel : + 41.21.693.52.48fax : + 41.21.693.53.28
e-mail : boulic@ligsg2.epfl.ch

Abstract

A new approach is presented for the animation of articulated figures. We propose a

system of articulated motion design which offers a full combination of both direct and

inverse kinematic control of the joint parameters. Such an approach allows an animator to

interactively specify goal-directed changes to existing sampled joint motions, resulting in

a more general and expressive class of possible joint motions. The fundamental idea is to

consider any desired joint space motion as a reference model inserted into the secondary

task of an inverse kinematic control scheme. This approach profits from the use of half-

space cartesian main tasks in conjunction with a parallel control of the articulated figure

called the coach-traineemetaphor.In addition, a transition function is introduced so as to

guarantee the continuity of the control. The resulting combined kinematic control scheme

leads to a new methodology of joint motion editing which is demonstrated through the

improvement of a functional model of human walking.

1

Kinematic control, either direct or inverse, has proven to be a powerful technique for

the interactive positioning and the animation of complex articulated figures. Although

expressed in the joint parameter space of these structures, direct kinematics is still widely

used to design complex motions from live recording, biomechanical models or key frame

interpolation. This space, henceforth referred

to

as

joint

space,

is

more

suitable

to

represent and capture the intrinsic dynamics of

motion.

On

the

other

hand,

motion

expressed in cartesian space is the basis of goal oriented motion.

Inverse

kinematic

control, the simplest tool to map cartesian motion onto the joint space, has shown good