Earlier in the course, the importance of structuring objects was highlighted. When objects are to be animated then the structure is crucial.

In order to animate a hierarchy of objects, we use keyframe animation and an interpolator on each node in the hierarchy that we want to transform, taking into account that child nodes are transformed relative to their parents. Note that this is conceptually very simple, it can quickly become complicated if there are lots of nodes that need to transformed!

In systems like VRML97, MPEG-4, and Java 3D you would typically have a single clock (time sensor) for each animation sequence. The clock controls (via routes) a set of interpolators, that each control a node that is transformed as part of the sequence.

A general tip when creating animation in this manner is to design and implement the animation in a top-down manner. Animate the objects at the top of the part of the scene graph that is to animated first and then animated and refine the child nodes.