Put this section before "Different packages available"

What about animation?

A rendered scene can be impressive, but images really start
to come alive when they are animated. A moving scene has
real depth, with objects in the foreground moving faster
than objects in the background.

Most rendering packages are designed to deal with
animations. They allow objects to be "key framed": for
example, in frame 1 a car may be on the left of the screen.
In frame 100 it may be on the right. The in-between frames
are calculated by the rendering software.

There's a lot more to it than that of course. Cameras and
light sources can move too: your camera can fly through a
cityscape for example, whilst the sun rises and sets. Or the
objects themselves can change over time: altering their
shape, colour and textures.

The best rendering packages allow objects to more in
realistic ways by allowing them to be linked in a hierarchy:
for example, given a human hand object constructed from a
disk and five cylinders, it should be possible to move the
hand in one go rather than having to move all the parts
individually.