36

walking, ground contact typically occurs in the previous state (S6 or S3) toward the end of the

swing leg extension. These two scenarios are illustrated in Figure 3.9.

S6
S1->S2

S1->S2

S2

S6

S2

S6

S1

left foot in

ground

contact

Figure 3.9 -

both feet

in ground

contact

(double-

stance)

(a)

right foot in

ground

contact

left foot in

ground

contact

right foot in

ground

contact

flight

(brief)

(b)

Possible walking and running steps described by base PCG of
Figure 3.7. Related states and transitions are indicated.
(a) walking
(b) running

An initial state must also be chosen for the walk. The initial state provides a starting position from

which a successful walking motion can begin.

While the simplest initial state to use would have

the creature at rest in the reference position, it is easier to achieve a limit cycle when the initial state

more closely resembles a state on a balanced walk cycle.

currently requires trial-and-error on the part of the animator.

Finding an appropriate initial state

Figure 3.10 shows the initial state

which was generated manually for the simple human model controlled by the base PCG of Figure

3.7.