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5.WALKING VARIATIONS

The ability to control walking characteristics such as speed, direction, stride rate and posture is

important if a system is to be seriously considered as an animation tool.

This chapter first

introduces an approach to controlling the speed of a walk without requiring changes to the

underlying base PCG.

Next, the idea of using parameterized base PCGs is introduced and a

number of interesting variations on the basic walk are described.

The idea of parameterizing an open-loop control structure such as PCGs is not entirely new

[vKF94b].

However, the successful parameterization of dynamically unstable motions such as

walking does represent an important advance.

5. 1

Speed Control

The basic balance control discussed in Chapter 3 uses fixed values of Q^dfor all steps of a walk

and achieves constant walking speeds. One possible way to vary the speed of a walk is to provide

a number of base PCGs which yield various speeds and interpolate between these.

This approach

might be somewhat cumbersome, however, since it requires the animator to provide suitable base

PCGs. An alternative is to allow Q^dto vary from one step to the next instead of remaining fixed.

By varying Q^dto cause the biped to speed up or slow down each step, a wide range of walking

speeds is possible without requiring modifications to the base PCG.

This approach requires that

we be able to affect the speed of the walk in a consistent manner by varying Q^d
.

Whether or not

this is possible depends on the choice of control system parameters (RVs, LPPs, etc.).

With the

choices described in Chapter 3, an intuitive form of control is available.

In qualitative terms, an

increase in speed can be achieved by using a more forward-leaning value for Q^dand a decrease in

speed can be achieved using a more upright value for Q^d
.