“This is what you have to understand with Tony Scott,” says Asylum VFX CEO Nathan McGuinness. “He is not a VFX director. He has no desire to make VFX films. He loves his in-camera techniques. He does everything he possibly can to shoot as much as he can in camera and get everything real.”

Working with Scott means leaning on the director’s proven capabilities as an action filmmaker, opting for practical, in-camera effects whenever possible. That keeps McGuinness, who’s worked with the director since 1998’s Enemy of the State, on his toes. “Tony will do anything he can to avoid a visual effect,” he says. “When I do step in, no one should ever realize there was a visual effect there.”

Scott’s new film, the thriller Unstoppable, is a taut story told nearly in real time about a runaway locomotive referred to as “Triple 7” loaded up with highly combustible cargo. As one character puts it, it’s a missile the size of the Chrysler Building. When a couple of railway workers played by Denzel Washington and Chris Pine find themselves on the wrong track at the right time, it’s up to them to figure out a way to stop the train before it levels a town in eastern Pennsylvania.

Movies like this – a little more than 90 minutes of impending disaster – generate real tension when the audience believes in what it sees on screen. Unstoppable could not look like a big, live-action cartoon, and Tony Scott would never allow it anyway. Asylum VFX worked as the main visual-effects company on the film, and McGuinness and Paul O’Shea worked together as VFX supervisors with the goal of making their work as transparent as possible to the finished product.

Most of the train footage in the movie was acquired in camera, but there were instances where a CG train would have to stand in, or where extensive roto, rig removal, and other touch-up would come into play. At key moments, the train needed to nearly fly off of the track due to its sheer speed. That required an animated train that could lean precariously over a single rail as it took a curve. In some shots, two trains interacting on the same track were photographed on location with a flatbed joining them. When Asylum removed the flatbed, the trains seemed to be barreling separately down the same track.

But in other shots, Asylum deployed a full CG model of the Triple 7, reconstructed with painstaking accuracy from the real train used in principal photography. “It was so photoreal that Tony just accepted the fact that it was CG,” McGuinness says. “In the three or four months we were shooting, our survey team lead, Greg Stuhl, surveyed the Triple 7 from head to toe. Every inch of the train was covered, all the information on its scale was recorded, and every texture was photographed. We brought that back to Asylum and started this immense build.” John Hart led the texture team on its daunting, laborious task of texturing the two engines and 25 consists.

The train, modeled in Maya, was key to the project. Asylum relied heavily on all of the information gathered on set to keep the model as true to life as possible. “It was a very heavy model,” says McGuinness.

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Mass in Motion

The next task was animation – figuring how something that big and heavy should move when it’s traveling at very high speed. The VFX team selected one live shot of the train to use as a reference. “We picked up one hero scene [from the shoot] and made that our test plate,” he explains. “We rendered CG out on the same plate and did a head-to-head comparison. That gave us the ability to analyze the differences in the movement, lighting, and texturing. It was a gauge to help us get it as photoreal as possible.”

And how do you make a CG model look absolutely massive? It’s not easy. “We always questioned ourselves when it came to the scaling of the train on the track,” says CG supervisor Bret St. Clair. “We had all the appropriate lens information, but sometimes the train looked different in scale. We had a back-and-forth with scale and weight and speed. Our animation lead, Michael Shelton, and team had to do a lot of pre-vis and test animation before we took it all the way through to final.” Modeling and animation were done in Autodesk Maya, texturing and lighting in Pixar Renderman.

One more piece of the picture was front-end replacement for the Triple 7. As the movie progresses, the train suffers more and more damage. To make sure the scars on the front of the train matched throughout the edit, Asylum built four different CG front ends, seamlessly replacing them to align with continuity.

That was actually harder than it might sound. “Pretty much everything Tony shoots is on a long zoom lens, and we had to track cameras that were looking through trees,” McGuinness notes. “Tony was stacking up the elements in the foreground of the frame to give the illusion the train was moving faster than it was. So we had a nightmare of a challenge when we had to track through trees and other elements.” The bulk of the compositing, led by VFX supervisor Paul O’Shea, was done in Asylum’s workhorse Autodesk Inferno and Flame systems. The Foundry’s Nuke was often used to composite CG elements.

Riding the Stanton Curve

Another key element of Asylum’s work involved the Stanton Curve, a dangerous stretch of elevated track that runs right next to a refinery. The track is real; the adjacent refinery does not exist. “When I went out there and looked at the location and saw the giant open field full of holes in the ground, it was kind of daunting,” he recalls. “We all know we can build CG and build environments, but we had to build elements to go inside that location. Remember, we weren’t doing a full CG scene. We had to be really careful that what came out didn’t feel like a CG world sitting inside a live plate. When you look at the finer points of camera tracking, there was no room for any kind of error because it would show so easily in the grand scheme.”

Asylum looked at refineries around Pennsylvania, studying their textures, layouts and pipework, in order to build a 3D refinery that could support Scott’s ideas for the sequence, including his trademark complex camera moves. “We went back and forth with the design, and it became a very successful, realistic, nobody-knows-we-were-there sequence. I always joked to the staff, ‘This was the same level of detail that went into building the environments when Ridley [Scott] did Gladiator!’ It was that same level of detail on the Stanton Curve.”

But the Stanton Curve sequence doesn’t look like Gladiator – the illusion never draws attention. That’s just how McGuinness likes it. “You can see in the reviews that people don’t understand there were digital effects,” he says. “On this film, the VFX company was in a supporting role. We weren’t leading the film in any way. In our world, we’re there to service a filmmaker’s film. Not a VFX film.”