Motion specification in animation

Motion specification tells the animation system how objects move, i.e. their position, orientation and size over time. The main methods are:

1. Direct motion specification

The animator gives the position, rotation angles and scale factors for each frame or key time directly (e.g. rotate 30° and translate 5 units per frame). Simple but needs full manual control.

2. Goal-directed (high-level) specification

The animator states the goal in general terms ("walk to the door", "pick up the cup") and the system works out the detailed motion. Used in robotics and character animation.

3. Kinematic specification

Motion is given using position, velocity and acceleration, without considering forces.

• Forward kinematics: joint angles are given, end position is calculated.
• Inverse kinematics: the end position (e.g. hand) is given and the joint angles are calculated.

4. Dynamic specification

Motion is calculated from physical forces and torques acting on objects, using Newton's laws (F = ma). Gives realistic motion such as falling, collision and cloth.

5. Keyframe specification

The animator defines key frames (important positions), and the computer produces the in-between frames by interpolation (linear or spline).

Key frame 1       in-betweens        Key frame 2
   O      ->     o    o    o    ->      O

6. Procedural / scripted specification

Motion is controlled by an algorithm or script (e.g. particle systems, flocking, rotating fan).