The Batpod's key feature is the pair of oversized tires that come from the front end of the Batmobile. The digital Batpod was built from a detailed Lidar scan of the actual practical stunt bike.

A New Environment
In the movie, Gotham City is portrayed as a super Manhattan island, completely surrounded by broad rivers and the open ocean. In Batman Begins, Nolan had started to reveal this maritime environment with brief shots of the Gotham River and a small number of scenes set in the Gotham dockyards, all sequences created by Double Negative. In The Dark Knight, the viewer will go right out on the water, looking back at the city while a hijacked passenger ferries float helplessly, completely at the mercy of the Joker.

To create the water surfaces, the team rewrote their dnOcean toolset, which uses Fourier Transforms to simulate a variety of wave types. A powerful water surface shader set then completed the effect. "We optimized dnOcean for speed, and also added new feature to create the wind patterns that you often see affecting large bodies of open water," Franklin explains. "Whenever you see the ferries, they are 100% digital, except for moments when they are seen in close-up at the dockside with the actors: a small section of the stern was built as a physical set for that. All of the water in the ferry shots is always completely digital, as it was easier to replace everything in the shot rather than try and blend the digital water with the real water in the plate."

The ferries themselves were based on the Staten Island ferries that shuttle between Manhattan and Staten Island in New York City. The team traveled to New York along with a crew from Lidar VFX services, and documented the actual ferries. A highly detailed digital model was built from the data and textured to work in close up at IMAX resolution, though in the final event, all the shots were delivered in standard 2.35:1 format. Passengers for the ferries were created by shooting extras as greenscreen elements that were then placed on cards and tracked into the shots with Double Negative's dnPlane-it 3D compositing toolset.

From Batmobile to Batpod
Besides creating Gotham City, Double Negative was also in charge of all the key visual effects involving the Batmobile and Batpod. The company had already created a digital Batmobile for Batman Begins, but the vehicle only appeared in long shots. "Initially, we had expected to be doing more of the same for The Dark Knight as the actual physical Batmobiles created by Chris Corbould's special effects team are capable of just about any kind of stunt," Franklin suggests. "So, we restored our digital Batmobile model to the system, and began to clean it up for background duties. However, it soon became apparent that the only application for the CG vehicle would be during the scene where the Batpod emerges from the car's wrecked shell.

"This would require our Batmobile to pass muster in extreme close-up at full IMAX quality. Furthermore, this necessitated replicating the look of the wrecked car rather than the clean version seen in Batman Begins -- the match needed to be perfect as we cut from a live action shot of the real Batmobile to a digital version within the same shot. The team worked very hard to get the level of detail up to scratch, and we liked to joke that our digital version was more detailed than the real thing as we added a whole bunch of interior details (revealed as the Batmobile transforms itself into the Batpod) that didn't exist in the real car…"