Paul Franklin.

To everyone's satisfaction, many of the Gotham City geometries that had been built for Batman Begins could be reused for The Dark Knight. One exception was the art deco Wayne Tower, which was completely redesigned for the new movie. "Most of what you see in the finished film is actual Chicago," Franklin adds. "We used visual effects sparingly to extend and enhance the location material only when needed, such as when Chris Nolan wanted to sell the scale of Gotham or when it just wasn't possible to get a plate of a location from the angle needed."

All of the CG assets were completely overhauled, remodeled to higher tolerances and then retextured to hold up to the greater scrutiny of IMAX -- and also to the fact that the new movie featured a lot more daylight photography. The only item that was reused without any modification was the Gotham City Monorail System, as it only played in two shots in the far background.

Rebuilding Gotham
The team found out that a whole new library of photographic material was required to cover the new locations that The Dark Knight used in the city. "For Batman Begins, we had mounted an extensive stills documentation of the Chicago locations – shooting almost one million digital exposures -- but the demands of IMAX and the varied lighting conditions of The Dark Knight lead us to beef up the stills library to get the results we wanted," Franklin observes. "Fortunately, digital stills technology had moved on, and the Canon 1DS MkII digital SLRs enabled us to shoot much faster and at much higher resolution than when we were working on Batman Begins. This lead to a change in our texture gathering strategy: rather than shoot the real buildings under beauty-lit conditions and then re-project the images directly onto digital geometry, we were able to wait until the buildings were completely flat lit in the shadows -- we have a piece of software called dnSun which allows us to predict exactly where the shadows will be in a city at any time/date. We then shot the textures in that brief window of opportunity before the light changed. This would then serve as a base level texture which could be re-lit digitally to match any lighting setup whether it was day, magic hour or night."

Geometry was captured in a number of ways. The team worked with Lidar VFX Services to digitize key locations, and also mounted their own surveys of all locations. The data was then used to reconstruct architecture directly from the texture reference stills via photogrammetry. All the data was collated by the modeling team, which then constructed the digital models, textured them and did the initial base-level look development.

Double Negative created a library of 40 hero buildings that were developed to work in day, magic hour and three different nighttime setups. 

Double Negative created a library of 40 hero buildings that were able to sustain close-up scrutiny. Each building was developed to work in day, magic hour and three different nighttime setups. "In addition to this, we had a huge library of low-resolution background buildings covering most of downtown Chicago," Franklin continues. "We also built detailed models of specific locations, including the Lower Wacker underground roadway, LaSalle Street (the site of the Batpod chase/truck flip scene). These models included accurate models of the actual road surfaces, which turned out to be essential later on during the car chase sequence. All items were built to work in hero close-ups with very high-resolution textures, and the shader set was able to efficiently manage the resolution requirements. The aim was to be able to reproduce as a minimum requirement the same degree of flexibility with our scenes that a cinematographer would expect to have on a real location. Our dnAsset digital asset management system has a good system for handling multiple levels of detail, which can either be automatically or manually selected."