
242 6. Computer animation
Gravity is assumed to act in the negative z direction and r is a radial coordinate
along the direction in which the projectile will fly.
From the point of view of describing the action in the context of practical
animation software the initial velocity V and projection angle α are probably
less desirable user contr olled parameters than say the point where the projectile
is to hit th e ground or where it is to reach maximum height. If either of th es e
are specified then the equations can be rearranged so that not only appropriate
V and α are determined internally but the direction in which the projectile is
launched is also