Chris Edwards of The Third Floor says it's important to hit a project hard and fast. Above is a comparison of images from a Jeep commercial from studio. Courtesy of Brand New School, BBDO, and Jeep. 

Nic Hatch of U.K. previs house Nvizage says previs helped quickly work out mechanical issues for the shoot of next summer's Batman Begins sequel The Dark Knight. "Solving mechanics in a workshop can take a long time," he says. "It's a lot quicker for us to do something in Maya and we can come up with a concept really quickly and show the director."

Chris Edwards, CEO of The Third Floor, says it's important to hit a project hard and fast. Third Floor uses asset builders early in the project, though that has increasingly come to focus only on a film's custom elements because the firm has developed an extensive library of assets for objects and camera rigs that can be reused.

While some of the previs assets can be exported for vfx houses to use, the process is more concerned with the creative elements. "We're kind of production indifferent," says Frankel, citing Live Free or Die Hard, on which he says they prevised a complex chase sequence without regard to whether CG or miniatures would be used to create the final effect.

The previs also can set parameters for what's needed in a location. Josh Wassung, a senior artist and co-Founder of Third Floor, says previs helped define the location for the final battle in Andrew Adamson's upcoming The Chronicles of Narnia: Prince Caspian (from Walt Disney Pictures in association with Walden Media). "We had some possible locations in mind and we tried them out," Wassung adds. "He wanted larger."

Frankel says previs was essential to planning a set piece in Constantine. © 2005 Warner Bros. Ent. Inc. All rights reserved. Courtesy of Proof.

Wassung then worked out in previs a location large enough to satisfy Adamson's direction and then a list of parameters was given to location scouts who were able to find a match.

Frankel recently prevised I Am Legend, Sony's upcoming adaptation of the classic Richard Matheson sci-fi novel, directed by Francis Lawrence and starring Will Smith. Frankel worked on location in New York, assisting in shadow studies that were essential to the story, as Smith is pursued by creatures that avoid sunlight.

"Where can they film in Manhattan so they can get this sundial effect of the shadows marching across the street?" he offers. "At the end of the day, a lot of this did boil down to, 'The shadows will fall there at this time,' and getting down to the architecture."

On Lawrence's previous movie, the comic-book adaptation Constantine, Frankel says previs was essential to planning a set piece in which Keanu Reeves' character runs down a derelict freeway in hell. Frankel suggests previs enabled them to map out the action, figure out how many real cars were needed for the set, where the camera platforms had to be to film the scene and how the visual effects would fit into the shot. "We didn't want to have to go to the effort of creating stuff only to have it be on the edge of frame," Frankel continues.