The process works just like in 3d live shooting, but the pair of digital cameras takes the place of real ones within the 3d environment.
The cameras are positioned and oriented in order to recreate the vision of the left eye and the right eye, as with the real cameras, but without movement and rotation constraints.
This kind of process becomes necessary when the 3D video to realize foresees subjects or environments impossible to shoot in the real world, in these cases through 3D modeling and animation they become achievable.
Also the management of digital cameras is more accurate, because it's governed by mathematical functions, after having set parallax and convergence, this will provide a 3D video processing stereoscopically perfect.