London-based Double Negative handled the electrifying, 250-shot sequence led by Ged Wright, the visual effects supervisor. The Dneg team also included Victor Wade (2D supervisor), Katherine Roberts and Jordan Kirk (co-CG supervisors). The Singapore office, meanwhile contributed compositing work throughout.
DNeg's work encompassed three areas: recreating Monaco (including crowds and historic cars); Whiplash's electric whips and their damage and destruction; and the MarkV Iron Man suit-up and armor.
DNeg accompanied the 2nd unit crew to Monaco in May of last year (just before the Grand Prix) to shoot digital stills, collect reference video and gather Lidar and survey data for the entire racing circuit and most of the surrounding city and terrain. In June, principal photography began at Downey Studios in LA, where a partial recreation of the fight area was constructed. DNeg collected extensive reference data of the Downey set to build a digital equivalent to incorporate into the wider digital Monaco.
The team took 100,000 digital stills, most of which served as the basis for the digital Monaco. Track, barriers, chain-link fence, stands and press box were all modeled and textured. The 500-foot-long Downey set was further extended to incorporate authentic Monaco surroundings (15 yachts populate the visible waterfront), and was once again modeled and textured.
Every car in the race is digital, for which DNeg created two highly detailed digital versions for each of the 11 cars. In fact, five art department cars were built specifically for the Monaco race and six genuine vintage Grand Prix cars were brought in to supplement the grid. Throughout the sequence, sprite crowds and practical crowd elements were used to populate the stands and buildings with CG agents used to break up the sprite crowd.
In keeping with the creation of the Iron Man Mark 1 suit, the Whiplash rig is homemade and very rough around the edges. According to Double Negative, this prototype quality was important in defining the quality of the whips. Although the whips slice through Iron Man's armor and generate a powerful stream of plasma, which runs along the length of the whip, the engineering is crude and prone to leakage. Also, the power source of the whips is similar to Iron Man's RT and required a similar repulsor blast look established in the first film.
Houdini  was used for the core whip effect, generating dozens of different passes with varying degrees of amplitude, frequency and motion blur. The whips also generate sparks, smoke, molten drops of metal, grounding arcs and a visible trail of energy, for good measure. The whips have a grimy, industrial feel in keeping with real world metal cutting equipment -- and director Jon Favreau's aesthetic. As for damage, the whips scrape and gouge the track surface, slice through several cars and tear up Iron Man's armor. The car slices were achieved practically, but required CG enhancement with photoreal CG sparks, embers, molten-metal, smoke, dust and flying chunks of debris.
However, arguably the greatest creative and technical challenge for DNeg was the Iron Man suit-up. The suitcase posed a conceptual challenge for deployment and assembly of the armor, while the choreography of the close-quarters fight between Whiplash and Iron Man offered a different challenge.
To solve the suit deployment the team looked closely at the Mark III suit-up in the first movie but then departed from conventional wisdom by having the case start deploying while still on the floor so that when Stark lifts it to his chest, the armor is already partially formed. This also helped to balance the pacing of the suit-up so it wouldn't feel like the viewer was missing part of the action or that it was overly compressed as a cheat.
The final Mark V Iron Man model was comprised of thousands of individually modeled and textured components. The armor has a distinctive deep red color, originally conceived as a clear-coat finish combined with brushed metallic silver. The final look was more of a traditional Iron Man red finish coupled with chrome silver.
Motion capture clips were used to rapidly block out Iron Man's performance through the fight. This went through several animation passes to achieve the desired heroic style. Posing and movement were critical, and the DNeg team developed a collaborative relationship with the editing team in LA, changing animation, shot framings and timings, while also creating new CG shots and offering a mini-cut of the material.
Bill Desowitz is senior editor of AWN & VFXWorld.