28. A method as in claim 1 wherein the step of refining an abstraction-based model additionally comprises the steps of: creating multiple abstraction-based model versions of visual object, the abstraction-based model versions being at different levels of modeling detail; and using different ones of the abstraction-based model versions in given iterations.
28. A method as in claim 1 wherein the step of refining an abstraction-based model additionally comprises the steps of: creating multiple abstraction-based model versions of visual object, the abstraction-based model versions being at different levels of modeling detail; and using different ones of the abstraction-based model versions in given iterations. 29. A method as in claim 28 additionally comprising the step of: presenting an interactive display of an intermediate scene model from a given iteration whereby a user specifies which one of the abstraction-based model versions is to be used in a subsequent iteration.