The thing to remember is that they are
probably
mixing actual footage(w/ pyrotechnics and whatnot) with CG. An
example
would be in Dinosaurs with the background bieng actual and the dinosaur
and
other objects being digital.
If you were to recreate the world(with
tree include
files that have many branches, radiosity, media, plus any isosurface) it
would
take a tremendous amount of time to parse and render. I'm talking
about
scenes that would probably require a better computer (at least better
that my
worthless Compaq). Such computers as those nice $20,000 SGI's (a
little
out of my price range)
Brendan Orr