Because of the enormous computing resources required for the simulations, Luma broke the task into a number of component parts. It first created low resolution versions of each shot in order to determine the proper volume and velocity and later rendered the scenes out in full detail (occupying several terabytes of data, some shots took several weeks to simulate and render). To add additional realism, a team of FX animators worked solely on foam, spray and interactive splash elements.

Additionally, Luma devised a unique system for rendering only those aspects of the simulation it needed. "One technique was called the 'frustum clipper' which allowed us to cut off details not visible to the camera," Cirelli said. "If we didn't need to see the simulation that was around a corner, we didn't calculate it. We'd wait until we got there. It was a modular approach."

Integrating the live talent into the CG tunnel sequence required some ingenuity. The actors were shot against green screen and Luma devised a way to apply motion data from animation onto a gimbal rig that controlled the motion of the real boat.

"This motion data along with animatics of the actual film set helped articulate the physical camera's relationship to the stationary boat and ultimately recreate the dynamic spirit of the previz," Swanson explained. "We then tightly match-moved the actors' in order to generate three dimensional shading. This in turn allowed us to composite the live action plates into the mottled light and shadow of the tunnel."

Among the most memorable features of the film is a giant mole that bursts through floors and walls in a ravenous search for anything to eat including the stories main characters. Based on a real-world animal called a star nose mole, the design considers what might happen to this tiny creature if it were left with no natural enemies for centuries. The result is a massive lumbering beast crowned with pink, finger-like nose tentacles that squirm and thrash about with creepy effect.

"The director, Gil Kenan wanted the nose to tell the story," recalled Raphael Pimentel, Animation Supervisor. "The creature uses it to sniff the air and it's the thing that telegraphs information to the rest of the body. The nose moves, then the body follows."

Luma made use of a variety of real world references in designing the look and action of the creature. Its lurching motion, for example, is modeled after a sea lion. Its claws provide the ripping force necessary to tunnel through dirt and rock. "It needed to have enough speed and agility to keep up with the kids, but at the same time had to express its girth and weight. We didn't want the body to move in a rigid way, but it also couldn't roll or bunch. We needed it to move like a pillow sack filled with lard." Pimentel observed. "The end result is a heavy and desperate motion that makes for a very interesting creature"

Making the mole look realistic at its larger size was also a challenge, added Cirelli, "Details in the skin of an animal are proportional to its scale and you have to take that into account when they become gigantic. You can't just make everything larger, you have to take into account what the larger animal is interacting with in its environment and how that might affect the skin and fur."

Although Luma has had previous experience with effects similar to all those employed in CITY OF EMBER the combination and larger scale made the project unique, noted Cirelli. "Over the years we have taken on projects that have allowed us to not only to expand the capabilities of our pipeline but improve the skills of our staff as well. We are continually impressed with the ability of our team to rise to any challenge that we put in front of them, they are a great group to work with and we are always proud of their achievements."

Credits for Luma Pictures go to Payam Shohadai, Exec Visual Effects Supervisor; Vincent Cirelli, Visual Effects Supervisor; Steven Swanson, VFX Supervising Producer; Justin Johnson, Digital Effects Supervisor; Pavel Pranevsky, CG Supervisor; Chris Sage, Lead Environment Artist and Raphael Pimentel, Animation Supervisor.