For anyone interested in modern VFX integration and how/why digital set extensions are done nowadays, this is a good breakdown of the process. Granted, this was back in 2005 or so and the main difference is that these days they spend far less time planning this stuff out and just shoehorn as much as possible into CG. So much so that if this was done today, they would be fucking with the camera move during the entire production, eventually turning the shot into a 99% CG shot with just the actor's head composited onto a digital double.