Meanwhile, MPC worked on another effect: the mysterious waterfall that disappears after becoming a whirlpool. "We came up with an approach that we thought would work because we had a lot of confidence in our water sims," Nordby continues. "The waterfall appears both as a day and night shot, so we had to integrate with the water. And the night shots play a pivotal role in the film, and we do a huge crane over. But we couldn't lock it to a pan or to a tilt, but we did have movement in all three axes, so we knew we'd have to be projecting. I shot as much HDRI as I could, which was difficult to get to the actual base of the waterfall, but I eventually lowered down a shot -- a ton of reference of the area because I knew we'd have to do some digi-matte work to recreate the basin that the whirlpool ends up in. And then when it came time to work on the shot with the water sim, what we ended up finding is that we couldn't get that massive amount of churning and foam to read as real as the location. Even when we cranked up all of those parameters, it ended up looking a little too placid, so we took a step back to readdress it.

"The CG Supervisor, Pete Dionne, came at from a different point of view. He grabbed chunks of that river and tialing it so that it had a nice stretch of birds' eye point of view of the water that existed on the location in the lighting situation we were trying to match. And then he projected that onto a whirlpool of animated sprites and had similar enough texture to the actual water that existed there, but pulled control into lighting it and could add depth mainly to the center of it. The thing that really stuck out in the end was that you really need to pay respect to the land that exists right below your water. We were dealing with very shallow water, so that was the biggest learning experience on that shot."

Bill Desowitz is senior editor of AWN & VFXWorld.