Spoiler alert: This article describes some of the action sequences in the new Terminator movie. If you don't want to know details about some scenes, bookmark this article and come back to read it after you've seen the movie.
SAN FRANCISCO--What do you do if you're a filmmaker trying to capture a scene in which an onrushing tow truck slams into a parked car, sending the car rolling neatly up and over the truck's back, but you face the reality that the car, vaulted into the air by a cannon shot from below, actually flies high above the truck?
If you're making "Terminator Salvation," or T4 as it's known, the latest salvo in the 25-year-old series, you turn to the visual effects experts at Industrial Light & Magic and depend on them to solve the problem.
And solve it they did. Those who see the film, which opened Friday, will see the collision rocket the car into the air and, indeed, roll right over the back of the tow truck. They'll never know that in real-life, the car actually soared high and straight up into the air.
Why did it matter? According to Ben Snow, the ILM visual effects supervisor on T4--who had the same title on films like "King Kong" and ""--it had every bit to do with the film's story. In the scene, the driver of the tow truck is trying to derail a so-called mototerminator, a high-speed killer robot in the body of a super motorcycle that is chasing fast behind. But the mototerminator is an intelligent machine, and isn't so easily knocked down.
So, Snow said, the point of the exploding car is that it's supposed to fall over the top of the truck and into the mototerminator's path, providing the evil robot the chance to showcase its instant maneuvering skills. And to turn that high-flying car into something that looks, on-screen, just as the script called for required a whole lot of visual effects.
"Usually we try and do it" for real, Snow said, "but it would be a miracle with an effect like this. So you weigh if it's worth standing around with an expensive film crew for a day trying to get it. Do we have more than one go at it?"
Instead, Snow explained, the real-life footage of the car exploding into the air was enough for the visual effects team to get going on the computer graphics (CG) version of the sequence. They combined the real footage with a digital version of the car that was based on some still photos they'd taken, and then they simulated the desired rolling-over-the-truck effect using ILM's proprietary rigid body simulation tools in order to produce the CG version.
Snow said that the footage of the truck, taken from behind, was doctored with visual effects to show it from the point of view of the mototerminator, which has a heads-up display calculating what's happening with the car.
"The story point," Snow said, "is that this mototerminator is reacting to the car, and able to do an incredibly nimble evasive maneuver to get out of the way. So we're trying to tell the story of these things being really bad-ass."
In the past, a movie studio might still have tried to produce a similar effect but Snow said that filmmakers might well have been less likely to turn to CG for the effect.
"I think we would have tried a lot harder to get the effect for real with the car," he said. "I can now depend on effects. I can take existing material and re-project it and get it to do what I need to...I can count on the fact that I can get a believable rigid-body simulation of something like a crumpling, rolling car. I mean, we were doing those kinds of things (a few years ago) on "Twister" and "Star Wars." But if you compare the realism of what we're able to achieve now to what we were able to achieve five years ago, it's way more realistic now."
That sort of advance, Snow continued, means that Warner Bros. and director McG can "make a Terminator for the 21st century...updated to give it a more gritty, edgy feel. Instead a guy puppeteering the robot, we're able to have the robot running around and chasing people."
Explosions on a bridge
Another of T4's major action sequences involves a large-scale battle that includes several forceful explosions on a bridge high over a river gorge. But Snow said that since it was obvious that the filmmakers couldn't conduct the explosions on the actual bridge--the fantastic near Taos, N.M.--it was necessary to film the sequence in three different places and then blend the footage together using visual effects and CG.
The sequence was shot on the bridge, on a nearby roadway and on a set on a field in Albuquerque, N.M., where they could actually blow up a truck.
The sequence, then, involves combining footage from the three different locations, going back and forth between them depending on the severity of destruction in each frame, and using CG to patch them together seamlessly.
Snow explained that putting the sequence together meant marrying footage from all three locations, adding digital backgrounds when needed, adding railings to the CG bridge, and adding the CG truck to the bridge.
"We re-projected this onto the (CG bridge) so I could have the truck fall over the edge, because in the original, it didn't fall over the edge," Snow said. And "those sort of techniques are just some of the things that we've been perfecting over the years: re-projection, the ability to say, 'Well, we can go and do this, shoot at three different locations, and we don't always have to use blue screen.' ...We can make it so you don't know which bit of the bridge is CG."
And, importantly, it means that for the filmmakers, there's no worrying about whether they can fulfill the all-important script element of blowing up a truck on a bridge.
For Snow's visual effects teams, the hardest part of working on T4 was getting the film's molten metal sequence just right. This meant making a scene in which melted metal pours through a terminator look believable, even though it's done in CG.
"We have some very good fluid simulation tools that we've developed over the years," Snow said, "but getting the molten metal to pour in and through this skeletal robot and look believable involved a lot more computing power than we've (ever used before). That was surprisingly hard, given that in the end, it's only in a few shots." It's funny seeing the film now, Snow said, because it's over in seconds and took days and more than a hundred high-power processors to create.
By comparison, Snow said, previous fluid sequences in films like "Pearl Harbor" used 30 lower-power processors and were considered beyond state-of-the-art at the time.
Today, visual effects teams like those at ILM still struggle to do realistic digital doubles and CG fire, Snow said, but the barriers to such effects are breaking down rapidly. And that could mean that in the near future, filmmakers can turn to CG to get just about any effect they want.
"The sky is the limit with digital technology," Snow said. "We're not limited by physical constraint. And so there's no time for complacency."
On June 22, Geek Gestalt will kick off Road Trip 2009. After driving more than 12,000 miles in the Pacific Northwest, the Southwest and the Southeast over the last three years, I'll be looking for the best in technology, science, military, nature, aviation and more in Colorado, Utah, Idaho, Wyoming, Montana and South and North Dakota. If you have a suggestion for someplace to visit, drop me a line. And in the meantime, join the Road Trip 2009 Facebook page and follow my Twitter feed.