VFX Supervisor Ben Shepherd led his team at Cinesite into ‘Battle Los Angeles’ to create one of the movie’s signature looks, distinctive smoke rings signalling the airstrikes of an alien army laying siege to Los Angeles, fleets of military vehicles and a frightening vision of the aliens themselves.
|VFX Supervisor Ben Shepherd travelled from London to Baton Rouge just as the shoot began to start gathering data for his team at Cinesite. He met with production VFX Supervisor Everett Burrell and Director Jonathan Liebesman at the shoot location around a municipal dam area. “We exchanged ideas and held some creative sessions, mainly about military hardware and huge explosions at that stage,” Ben said. “I had on my team Dan Sewell as 2D Supervisor and artists including Compositor Dan Harrod, with experience from ‘Generation Kill’, which had initially attracted the director to Cinesite.”
“We reformatted and rebuilt the ‘Generation Kill’ assets to suit the new pipeline. The models and textures were used but quite a few technical differences existed in the hardware, such as different numbers and flare packs on the CH-46 helicopters. It took a while to get them all into the shinier, faster ‘Battle Los Angeles’ pipeline. They were based on actual CH-46, Super Cobra and E10 helicopters, humvees, light armoured vehicles, Abrams tanks and others, and they all needed subtle adjustments for the new film.”
A quantity of tracking markers was required on set, and Ben wanted to make sure the effects plates didn’t include excessive smoke from the special effects team working on location. Many of the plates as supplied for Camp Pendleton, a major sequence, were virtually empty of aircraft. Some shots looking out from the control tower showed only a long, clear runway. The production used three live action CH-46s, plus some Osprey helicopters that they had no CG assets for, normally placed in the plate foreground, which they could repeat over and over to populate the shot.
Better than Real
“Our software pipeline was based on Maya rendered with RenderMan, with Mudbox for modelling, and PFTrack, Boujou and occasionally 3DEqualizer for tracking. Compositing was almost all done with Nuke, except for the odd shot handled with Shake, still very quick to use for green screen work and cleanups. This was our first project using a full Nuke pipeline.”
The team was required to create water splashes to accompany the alien’s meteor strikes as they drop into the water. To make them resemble depth charges, they turned to online videos for reference. The splashes were used mainly early on in the story, in shots over the sea at Santa Monica and in TV monitor inserts. A close-up version was treated to resemble interlaced video footage, added as an effect in the composite. Cinesite also supplied the final matte paintings of the destroyed city, including the fallen alien machinery emitting its particular blue fire.
The shader controlled light interaction and penetration, texture, smoky detail and thickness. “First experiments with shape looked a bit like a jellyfish but refinements resulted in that very distinctive ‘Battle Los Angeles’ design, adding wobbles, adjusting speed, getting a kind of smoke ring airbrake effect. The simulations were entirely 3D so they could be rotated and rendered at different angles. In one shot the helicopter passes right through one as it goes off in front of it, shot in a shaky documentary style. It was great to finally watch these shots with all the camera and surround sound effects in place,” said Ben.
In a film filled with explosions from start to finish, Ben noted that handling them depended on the type of explosion and his team’s skills. A lot of 2D work was typically involved in adjusting and enhancing the explosions and layering various elements, especially dust. “Jonathan always liked us using YouTube and other video reference, including an Iraqi munitions dump exploding to watch how shock waves emerge at different angles.
“We put a lot of research into the realism, especially the speed. Water vapour compression shock waves also spread out at oblique angles, creating some interesting effects. We watched hours of explosions. I've found myself looking at newsreel footage of recent events like the Japan disaster critically and objectively, as if they are not real.” Other explosions were needed in the fire fight with the aliens in the sewer after Sergeant Michael Nantz descends from a helicopter on ropes to help stage an attack.
Explosions for the Santa Monica sequences were always at least based on a plate, with up to 80 per cent added as digital matte paintings. The most extreme case was perhaps the platoon’s arrival at the destroyed FOB, when all they had was the blue screen shot of the soldiers standing in front of a fence. In one of the tunnel sequences also, just the foreground actors were shot first and the extension of the aliens water-collecting activities were added into the background.
“The director wanted the aliens to move in a way that could be mistaken for human movement from a distance, especially the hand signals and gestures. Our team had a motion capture library but used it largely as reference,” said Ben. “Most shots were completed with keyframe animation. The motion capture was a combination of real Marines pretending to be aliens and actors pretending to be aliens working as Marines. Overall, our guide was to maintain a look that could be accepted as human at a distance.”
Cinesite’s aliens had a slightly different function and back story – the team called them the ‘Republican Guards’ – and therefore their own look and style of moving. The Commander was a special case, with a greasy, oily look when he was encountered down in the steamy sewer environment. The aliens also needed a dusty look applied to them, due to the battle conditions, particularly for the Commander as he climbs from underground with his gun.
“Where tracking challenges arose, in fact, was in some of the wide shots. Those with very slow, creeping zooms were often the hardest. We had to figure out exactly what the camera was doing, moving slightly perhaps, or panning just a little. The shakier shots could be more forgiving, because the motion blur of the shot could hide a glitch.
“When the soldiers arrive at Santa Monica airport, Aaron disembarks and looks around, viewing the damage. Many helicopters are landing in the background, and these were all difficult match moves. These shots were short and quick, and hard to track. We used PFTrack and Boujou - plus 3D Equaliser in this case, which is good with distortions - to make sure we had everything in place, and also used 2D matte paintings here for very distant views.”
“The scale of it, hanging overhead, had to be handled shot by shot. We started by tracking the camera, and had a Lidar scan of the set for the 3D environment. Once these were in place, all the character pieces and 3D models were put in. But once we looked through the 3D camera, the correct position for the Hovercraft often looked wrong, not imposing or frightening enough, and we would shift objects until we had achieved the right sense of danger and drama. We weren’t precisely scaling or deliberately ‘cheating’ the Hovercraft’s dimensions to look bigger, but shifted its position in some shots from the technically correct spot to cut together better in ‘film space’, if not ‘world space’.”
Words: Adriene Hurst
Images: Courtesy of Sony Pictures/Cinesite