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10 cgw n o v e m b e r . d e c e m b e r 2 0 1 5 fun, sincere, emotional story of friendship and discovery." DP Sharon Calahan, Produc- tion Designer Harley Jessup, and Sets Supervisor David Munier and their teams of artists worked together to create the environment through which Arlo and Spot travel. They coordinated with teams led by Effects Supervisor Jon Reisch and Simulation and Crowds Supervisor Gordon Cameron, who heightened the emotional setting with motion. The river, trees, clouds, grass – everything in the environment moves in sync with story points. "This film was an extraordi- nary collaboration between art, lighting, and all the technical teams," Jessup says. "We worked closer together than on any film I've worked on at Pixar. I don't think the film would have worked unless the settings were exquisite and nature was a big antagonist." A R I V E R R U N S T H R O U G H I T Arlo's first terrifying moment with the antagonist happens when he falls into the raging river. "The river propels us into the journey and provides Arlo with a means to get back home," Reisch says. "It's his yellow brick road. But beyond that, Pete [Sohn] insisted that the river itself reflect Arlo and Spot's emotions. When they first meet, the river is churning. When they connect, the river is glassy smooth. This was the biggest ef- fects show we've done, and the river was the biggest challenge." Thirty-one technical directors created the effects – twice that of any previous film at Pixar. And of the 900 effects shots in the feature, 200 were of the river. To understand how the river should look and behave, Reisch worked with Jessup and Calahan. "Sharon [Calahan] painted color strips and did pastels – early studies at different times of day to show the lighting and how much we can see under- water. Once we knew we were all pushing toward the same goal, we worked with technical directors to make sure we had the tools. There was quite a bit of development." Pixar has built its effects pipeline around Side Effects Soware's Houdini, and the team used that soware pro- gram's Flip solver for the river. To conquer the problem of simulat- ing a river that ran for hundreds of miles, the team divided the work into manageable chunks. "We did close to seven or eight simulations, each a quarter- to a half-mile in length," Reisch says. "It took half a dozen layers to get the surface, and more than that for the churning rivers. So, we'd parallelize at ev- ery stage. We'd surface in small chunks and then reassemble clustered sims into a coherent whole. We wanted Pete [Sohn] to have the ability to tell the story with the best assemblage of shots. We would integrate the modules and then light and dress them differently so the au- dience never saw the same river." Pixar's ability to draw on a 30,000-core renderfarm made it possible to handle the 17 tb of data churned up by the rivers. "The water was the thing that scared all of us the most," says Susan Fong, global technology and rendering supervisor. "We had to re-think our approach. My team wrote tools to help the effects team understand the scalability so we could handle the water and the simulation of vegetation. These were high- data scenarios. It took between 50,000 and 100,000 CPU hours to run the sims." To render the white water, the effects team decided to use volumes. "Before, we did white water with points," Reisch says. "The white water in this film is almost all volumes. We'd break down the detail in those volumes so we could store them on disk. With multiple levels of resolu- tion in one file, we could pick higher or lower resolution based on the camera." Placing the river into the set was an art in itself. To give Sohn plenty of elbowroom for location scouting, the sets team adapted approximately 65,000 square miles of US Geological Survey (USGS) terrain data. Ultimately, although USGS data provided the topology and the height data, the artists would change the terrain in Autodesk's Maya as necessary for story points. "In the past, we'd build fore- grounds and use matte paintings and matte-painted clouds to extend the world," Calahan says. "For this film, we used the USGS survey data and procedurally created detail using the "wonder AT TOP, SET DRESSERS WORKED FROM USGS TERRAIN MAPS TO CREATE THE VAST LANDSCAPE. AT BOTTOM, THE CG RIVER FLOWS THROUGH 200 SHOTS.