INVERSE KINEMATICS AND GEOMETRIC CONSTRAINTS FOR ARTICULATED FIGURE MANIPULATION

摘要

Computer animation of articulated figures can be tedious, largely due to the amount of data which must be specified at each frame.Animation techniques range from simple interpolation between keyframed figure poses to higher-level algorithmic models of specific movement patterns.The former provides the animator with complete control over the movement, whereas the latter may provide only limited control via some high-level parameters incorporated into the model.Inverse kinematic techniques adopted from the robotics literature have the potential to relieve the animator of detailed specification of every motion parameter within a figure, while retaining complete control over the movement, if desired.This work investigates the use of inverse kinematics and simple geometric constraints as tools for the animator.Previous applications of inverse kinematic algorithms to conlputer animation are reviewed.A pair of alternative algorithms suitable for a direct manipulation interface are presented and qualitatively compared.Application of these algorithms to enforce simple geometric constraints on a figure during interactive manipulation is discussed.An implementation of one of these algorithms within an existing figure animation editor is described, which provides constrained inverse kinematic figure manipulation for the creation of keyframes.iii Chapter 2 Approaches to Figure AnimationPlacing this work in context requires some understanding of computer animation techniques in general, and of how they may be applied to figure animation in particular.This chapter provides an overview of the advantages and disadvantages of basic motion control techniques for figure animation.The emphasis here is on methods to create and control the movements of articulated figures, rather than simply replaying digitized movement.It is fair to say that for many productions, digitizing, or rotoscoping, the movements of real subjects remains the method of choice for obtaining convincing life-like motion.Rotoscoping can refer to techniques ranging from visually matching graphic images to prerecorded video footage, to attaching some sort of sensors to a performer's body, whose positions can be tracked by computer and stored for later playback.Neither of these are particularly attractive options: the former being quite tedious, and the latter relying on the availability of reliable, unobtrusive instrumentation for the body, and sophisticated software to reconstruct the original motion from the sensor data, neither of which are readily available yet.A further limitation of rotoscoping is that a figure animated in this way is limited to those movements actually performed by a live subject.Computer animation techniques can be applied to animate figures in situations for which rotoscoping is neither a viable nor practical solution. Body Models ScopeFirst we must decide exactly what we are trying to animate.Although the ideal computer-generated 'Lcharacter" would include muscle and tissue that deforms during movement, skin and clothing that wrinkles and stretches, hair that flows, and expressive facial features, the accurate modelling, animation, and rendering of these attributes are research topics in their own right, and work in these