CGSociety :: Production Focus
18 September 2013, by Paul Hellard
Big bashing hot explosions seem to be the meat and potatoes of the VFX Industry at the moment, and White House Down had so many examples of particle blooms they became very much extra cast members. CGSociety spoke with Ollie Rankin, the VFX Supervisor at Method Studios, one of the group of studios called in to create these explosive starts. Method was the lead special effects vendor, and Rankin was the creative points person of the production, taking the vision of the director and Overall VFX Supervisors and Co-Producers for the show, Volker Engel and Marc Weigert at Uncharted Territory.
Method had 80 people working for eight months, working on 185 shots. Ollie Rankin tells of a visit to Uncharted Territory to visit Volker in LA. "They had a 'war room' set up. There was a big, round conference table filled with what they called 'big' shots and then there were the 'big-arse' shots. Grouped by sequence. Big red outlines drawn around the sequences and shots that needed really big attention. So many of them were ours. That gave me a real sense of the scale of the production."
"The biggest challenge on this film, was actually the fact that you can't realistically get into the Obama's backyard to film what you need," Ollie qualifies. "There is a pretty crucial no-fly-zone around the exact building we needed to fly around. There are certain areas around DC where you can get a chopper in and film though." But for the major shots, they weren't able to get in and shoot any practical plates on locations and so in those cases, everything had to be digital. The choppers, the crews, the WhiteHouse itself, as well as the surrounding grounds and backgrounds of the city of Washington DC. Where the faces of the pilots were visible, they were able to shoot this on a sound stage.
Since such a lot of the action occurs around the White House, they wanted to share the workload around the studios they had engaged. In the end, there were 12 different VFX studios working on various parts of the shots. Method took the lead role in building the CG White House which they then shared with all the other studios to keep the consistency of views of the model. The polygonal geometry and structures of the White House model were all built in Maya, while the textures were developed in MARI. "Because our primary pipeline in building the White House was going to be using lighting within Maya and rendering it with V-Ray," continues Rankin, "we did our shader material development in that configuration." Some other studios could then pick up the models and use them in their application of choice like 3ds Max and Softimage, maybe using RenderMan or 3Delight. "It was quite an interesting mixture of pipelines that needed to be conformed."
"These models are handed across in FBX and or Maya, accompanied by test renders so the receivers could be sure they could then do their inhouse render passes correctly."
Three helicopters get shot down in very different ways in this movie. Roland Emmerich was quite determined that each one had a unique demise. Then of course the most challenging structural destruction was the collapse of the Capitol Dome. Building the model of the Capital Dome began with having a look at all of the blueprints that are, strangely enough, available online. Method artists used them as the basis for building the dome that ultimately would then be destroyed in a particular way. "If it was to be only standing there looking like the Capital Dome, it would have worked and we all could have gone home, but there's a helicopter shot of the outside of the dome where a fireball erupts through the windows and blows out the glass, that was one of those shots where there was a very good plate filmed for it," explains Rankin. "They were able to get a good viewing of the Capitol."
Rankin found that when they tried to line the CG model up with that dome, there were some quite significant discrepancies. "The dome is quite old and was made with less exacting lines. There's been renovation, deteriorations and many changes to the solenoid case and shape." There was of course no chance to be able to line up, pixel for pixel, with the real one. "The best solution was to completely replace the dome on the plate with the CG one we'd prepared earlier."
They had a couple of things to work from. They looked at a lot of references of buildings collapsing. Even quarry blasts and that sort of thing. The concept artwork created by some amazing artists at Trixter in Munich worked with Roland, specifically on four frames of the progressions of a collapse of the Dome. "We used them as a guide for where the fracture points could be," says Rankin. "We could decide on the run, where the points of weakness could be on the pylons, arch and structure. Then we used a multi-pass procedural approach to do the rest of the fracturing. There is a procedural algorithm for breaking up polygonal geometry, but it created quite recognisable shapes. Those give the game away."
There were several tricks to cluster together some of these effects and in what would appear the correct place for it to slice. This all took some render power, so Method ran a primary pass which was just the outer shell of the building collapsing. When one piece of masonry hits another, it wouldn't break. This was where the secondary passes were created and generated and then added to the roll in the composite. There was also the internal metal framework of the building which would bend differently, and that was generated in a separate pass as well. Then there was grit and fine dust being given off at every breakage. "You'll see bits of falling masonry with smoking trails behind them as well," adds Rankin. "When the roof collapses, there's that downward movement of the dust as it follows the air, and all this has to react as well because its been burning for a couple of hours, in the story."
"The last effect we completed, was the first helicopter crash," added Rankin. "On fire, spiralling into the ground, the rotor blades smacking trees and churning up the ground with blades of grass, and soil being thrown around when it lands on fire in front of the White House Office next to the fountain. In the end, we had about 12 people dedicated just to that shot."
This group used a number of interesting techniques to make sure not to be caught out if changes were needed. The director was not really able to sign off on the animation of the helicopter and the camera angle until he'd seen it with all of those additional elements added in. "One approach was rendering the images as 'deep raster images'. What that means is that you're embedding the distance from camera into the render so that you don't have to precompute the layering of things. Normally, the most efficient way to render this is to start at the back, instead of rendering the lot, you omit the bits that are to be hidden behind something in the foreground. Makes sense, until you have to move something in the foreground. In rendering as a deep raster image, you can render the entire frame of every layer. We would be able to manipulate the layering order and change out any one layer that is changing everything else. This is all rendered at a much lower sample setting but it would show what was happening. Its the final render after sign off that takes many, many hours per frame."