The plane was built and animated using Maya, the main animation package at Animal Logic. Tracking and match-moving was tackled using Boujou, PF Track and 3D Equalizer. The team relied on RenderMan 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."

Previs helps plan out the subway car collisions. 

Colliding Subways
Animal Logic 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."

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

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.