<em>Knowing</em> the Future: Planes, Trains and Walls of Fire

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Catastrophe is something the vfx wizards need to know for Knowing [1]. All images © Summit Ent.

Director Alex Proyas has a strong track record of pushing the envelope with visual effects. From the shape-shifting buildings of Dark City to I, Robot [2]'s photorealistic robots, his movies feature unique ambiances and striking imagery. Opening today from Summit Ent. [3], Knowing, his latest film, definitely follows this tradition as some 400 visual effects shots recreate various disasters with an unprecedented level of detail. The catastrophes range from local tragedies -- plane crash, subway collision -- to global phenomenon.

In order to create those large-scale disasters -- and many other vfx, Proyas turned to Sydney-based Animal Logic [4] and Overall Visual Effects Supervisor Andrew Jackson [5]. The initial vfx shot count was around 200, with seven months of postproduction. Jackson and VFX Producers Michael Twigg and Luke Hetherington assembled a team that included 3D Supervisors Alfie Olivier, Andreas Wanda and Will Reichelt [6], and Compositing Supervisors Charlie Armstrong and Dave Dally.

Although the script called for some very spectacular imagery, Proyas wanted the entire movie to have a strong realistic feel. "It should all feel like someone with a camera had been there, on location, when the events took place," Jackson observes.

"It meant that we couldn't do anything that a real person manning a real camera couldn't have done in each particular location. Alex didn't want any fancy 3D camera move. The shots were all hand-held, and had to feel like the cameraman was trying to follow the action the best he could, just like in news footage. Even for the space shots, Alex requested that it all looked like the footage had been captured by a human cameraman."

According to Jackson, the team benefited from the fact that the movie was shot using the new RED digital camera [7]. "On set, one of the advantages is that you can just keep on shooting, and not worry about the quantity of film stock that you are using. Then, in post, you can access absolutely everything that was shot -- and that is a huge benefit for us. When the plates are shot in 35mm, you just cannot have everything scanned. You need to choose the plates that you need, and then justify the cost of having the scans done. That not being an issue in digital, it is absolutely fantastic! You have every single take and outtake available. Plus, they are all time-coded. So, as long as the data management is good, you can get straight to any particular piece of footage."

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On-set practical effects had to be combined with digital simulations for the plane crash. Images courtesy of Animal Logic.  [8]

Crashing a CG Plane
All the key effects sequences were extensively previsualized, including the crucial plane crash sequence. Proyas designed an elaborate shot in which a 747 jumbo jet is seen crashing across a freeway and into a field before the main character rushes to the crash site, all in one shot. "This shot was definitely a challenge," Jackson recalls. "There were 3,196 frames... When we got the plates, we first had to paint out the huge rain towers that were on location. Then, we rebuilt the scenery in the computer. Alex wanted to be able to modify the movement of the plane in post. To this purpose, we had shot a very slow pan that followed the path of the CG plane. We could then reconstruct the location digitally by using different techniques. The background was a matte painting, the major part of the scene was a combination of separate tiles that were shot on location. The 3D card technique allowed us to pan through them with the 3D camera. When the scene was recreated, we could precisely adjust the camera to the motion of the plane that was finally approved.

"Right after the plane has crashed, there is a whip pan back to the road where we switch to the live-action footage with Nicolas Cage. Then, the camera follows him on the crash site, which was a whole different set-up. The art department built a very detailed set with lots of debris, large airplane elements, practical fire and smoke. We augmented it with CG explosions, and practical smoke and fire elements. We also extended the length of the shot by panning over to another part of the crash site, and then pan back to Nicolas Cage and go on with the original shot -- this added part was never filmed; we created it in CG."

The plane was built and animated using Maya [9], the main animation package at Animal Logic. Tracking and match-moving was tackled using Boujou [10], PF Track and 3D Equalizer. The team relied on RenderMan [11] to render the 3D images, and on Nuke or Inferno for compositing. "The model was pre-scored in order to break apart during the crash," Jackson explains. "We used rigid-body dynamics to animate the smaller pieces, and hand animation for the larger pieces -- we wanted to have the possibility to 'art direct' the crash. We found tons of video references of actual plane crashes on the internet. That footage helped us to determine the exact motion of the plane. That was one of the trickier aspects of the shot. We needed to develop a motion that looked absolutely natural and real, but we had to judge that without all the other elements -- fire, smoke, debris, dirt projections, etc. It is very difficult to evaluate whether the motion of an object is correct or not when half of the elements are missing... We must have done 20 or 30 different versions of that shot!"

CGI was also utilized to animate vehicles and dirt that get thrown in the air during the impact. The final explosion was created using Maya's fluid dynamics tool. "We thought of utilizing some practical explosions elements, but ended up doing it all digitally. We felt that it carried the forward energy of the plane much better than the elements that we had shot. Yet, due to the sheer scale of the explosion, the simulation really pushed the limits of our machines. Simulating the effect in itself was fine, it was the resolution that was the problem. We needed an extremely high level of detail."

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Previs helps plan out the subway car collisions.  [12]

Colliding Subways
Animal Logic [13] faced an even greater challenge with the subway collision effects. During the scene, a runaway train crashes into a stationary train and destroys the crowded platform. "We had so many shots!" Jackson recalls. "The key to this sequence was that, first, we didn't use any bluescreen or greenscreen, and second, we put as much practical effects as we possibly could. We had hundreds of extras, practical dust, smoke, sparks and debris projections, all timed to the motion of the train, flashing lights, stuntmen on wires, etc. We completely filled up the frame, which turned out to be a really successful technique. You could cut the sequence together right after the shoot and have a very exciting sequence, even though the train wasn't there yet. We then added the previsualization train in the shots, which gave us a very good starting point to create the scene. The final train was built in five different versions, all featuring various levels of damage. We could just switch from one to another during the sequence to get the right amount of damage."

The shots were then enhanced with additional elements. Half-scale columns and half-scale platform edges were detonated while high speed cameras filmed the action from various angles in front of a greenscreen. Stuntmen were also filmed on wires to represent commuters being hit by the train. The resulting footage was then composited in the scene and synchronized with the motion of the CG train. The action was enhanced even further with the addition of a few CG extras.

In one of the most spectacular shots, the audience shares the point of view of the conductor inside his cabin, as the train mercilessly glides among -- and over -- dozens of people on the platform. "We mounted a camera behind a sheet of glass on the front of a quad bike, and drove it 'into' a group of stunt people. That formed the basis of the shot. We then added extra layers from various other takes and greenscreen elements."

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For the subway sequence, many of the effects were done on-set, leaving train itself the only missing element. Images courtesy of Animal Logic.  [14]

The End of the World?
The disasters in Knowing soon become global as a phenomenon ignites a huge wall of fire that engulfs Manhattan and other places. "The end sequence was our greatest technical challenge," Jackson notes. "Obviously, the sequence, as well as the plane crash and the subway collision, will remind some people of other disaster movies. We thought about that, but in the end, we decided that we shouldn't care. We just did our best for the visual effects to match the feel of the movie, and to make them as believable as possible. Plus, Alex's idea to immerse the audience in the action, rather than showing it from a distance, made the shots very interesting.

"The Wall of Fire required a lot of highly-complex fluid simulations, all created within Maya. We opted not to use practical fire elements, as we felt the scale of the event was so large that no real element could match it. The fluid simulation was built in multiple layers, but it was all driven by the main simulation, and then rendered together. In order to generate correct interactions with the buildings, we had to rebuild sections of Manhattan in the computer. So, I went to New York and shot aerial footage of the city. Then, we modeled the geometry of the buildings and projected the footage onto them."

Around Christmas time, a mere month before deadline, production requested a new series of shots for this sequence and others, which stretched Animal Logic's capacities to the limits. "Initially, the intention was that we would do the whole movie," Jackson observes. "But towards the end of the project, the scope of work grew considerably and got close to 400 shots. We felt more comfortable assigning those new shots to other vendors. In the end, we produced 247 shots for the movie."

Joining production to help guide the additional visual effects effort was Eric Durst [15], who also served as overall visual effects supervisor. "As in many films with extremely tight deadlines and a very large cinematic vision, the work often requires additional people at the end," Durst suggests. "In this case, enlarging the crew, including expanding the teams at Animal Logic, really helped preserve the high degree of detail and care that this project required. Andrew had been on since the beginning and was fully engaged in scenes such as the subway collision and the plane crash, among many others. My role was to help by supervising additional shots and scenes that required 100% attention."

Additional vendors included Postmodern Sydney and Haiku Post, which mainly focused on straight greenscreen composites and fix-up shots, and Buf Compagnie [16], which contributed five dramatic shots to the Wall of Fire sequence.

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Fire and smoke wasn't just limited to the Wall of Fire sequence. Fluid work was also needed for other elements of the film as well. Images courtesy of Animal Logic.  [17]

The Paris-based team was lead by VFX Supervisor Antoine Deschamps, VFX Producer Pierre Escande and R&D Supervisor Xavier Bec. "We had to create the wall of fire itself, as well as all the destruction in its path, and the fiery sky," Deschamps explains. "The fire had to look like a wave that would flow in the streets while buildings would explode and collapse. We opted for a full fluid simulation for both the fire and the smoke. Our R&D team also developed a new shader to handle explosions and smoke. In order to get a more organic feel, we added a lot of practical fire elements to the very front part of the wave."

The sequence necessitated the creation of up to 600 buildings for the really wide shots, which led the team to procedurally animate as many elements as possible. Low-resolution buildings were rigged to collapse via rigid-body dynamics, while high-resolution buildings, and their complete inner structure, were destroyed via matching animation. All the work was carried out using proprietary tools. The simulation was divided into various modules, some representing one hero building, others a whole city block. Yet, the shots were so complex that rendering still took up to 10 hours per frame.

"For closer shots on Time Square and Grand Central Station, we recreated the location using photogrammetry techniques," Deschamps says. "We then painted out all the pedestrians, the vehicles, and changed the billboards. For the aerial shots, we used helicopter footage and modeled the corresponding buildings. Every time a building would collapse, we had to reconstruct the building that was revealed behind it. Also, we completely relit the city by adding fiery reflections on the windows and on facades. It made the scene look much more realistic. For the space shot, we used texture elements that had been created at Animal Logic, and we added our own simulation."

In the end, Durst believes that one of the very interesting aspects of the project was doing the digital intermediate at Park Road Post in Wellington, New Zealand. "I was very impressed with the work of David Hollingsworth and his team, and the way he color timed the RED camera footage, building extraordinary cinematic and filmic feel to the movie. I felt it played an important role in the final result."

Alain Bielik is the founder and editor of renowned effects magazine S.F.X, published in France since 1991. He also contributes to various French publications, both print and online, and occasionally to Cinefex. In 2004, he organized a major special effects exhibition at the Musée International de la Miniature in Lyon, France.