Give me a break people! So many here 'think' they have a clue about 3D (aka stereoscopic) and CGI. Small parts of Avatar were shot with a single camera and made stereoscopic in post. Taking video from a single camera and converting it to '3D' is not difficult but is very time consuming. They use 'Rotoscoping' to cut out elements of an image and then create a 'left' eye and a 'right' eye. In fact, some types of shots are easier and better suited to shooting with a single camera due to the inherent difficulty with current stereoscopic 2-camera rigs. Anyone wanting to 'learn' more about 3D, go to fxguide.com.
Something no one has mentioned is that the length of Titanic makes it the worst choice possible for 3D. Even Avatar was too long to watch in 3D without getting at least a headache or even sick and vomiting.