Ray traced shadows posed another challenge. You get very sharp, detailed shadows; however, they're very expensive to compute. On the flip side, you have map-based shadows but detail gets lost. So they tried to combine the best of those approaches in a single method. Ray tracing for close-ups and map-based shadows as you get farther away.

There were also improvements to the driving system: one of them was when cars race on a curve when it's hard to do a sharp turn. "So we devised this program (which we've actually applied a patent for) that lets you skid off the path under animated control but then get right back on," Shah continues. "The system that computes the car's movement keeps the internal idea of where the car wants to be physically but then allows it to break free. This provided more creative flexibility to how these cars drive around."

As for covering all that ground with more than 120 original sets, Pixar tried to use a more procedural approach. "Or at least get the city blocked in, and then you can work in the detail for the foreground or the landmarks," Shah offers."So we used CityEngine. The way it works is you start with a roadmap for the city and that divides it into lots. London, for example, is a very old city with odd-sized lots and sometimes you get quadrangles in the middle of buildings, so it's interesting trying to solve that problem."

Indeed, London was the hardest to capture, according to Harley Jessup, the production designer. "We had to think of new strategies for that. CityEngine was customized and tailored to meet the challenges. The variety of Georgian and Edwardian and Queen Anne style buildings. We built a collection of parts that could be recombined in different ways that always looked like a Queen Anne brick and stone building or a Georgian graystone. It also had to have the 'carified' motifs also present in the façade. For example, the pillars on a Georgian building have shock absorbers."

Another improvement was the open ocean. "We wanted to take it further, so we wrote a new wave model based on the Tessendorf [surface] wave method," Shah adds. "Also we updated the shading model for our water so now it has better translucency with volumetrics."

They also built a procedural modeling system for the vegetation and a dynamics system to animate on. "The problem was with the old system was that we had a limited palette with trees," Shah continues. "And also the motion was not very robust. We wanted to go after a much more flexible authoring approach. So we built tools where we can do some of the procedural stuff in our own software, but then you can quickly go back and forth between Maya and Houdini and our own toolset to keep refining the tree as you build it up."

Krause concludes that Cars 2 definitely looks more beautiful than its predecessor (to learn more check out The Art of Cars 2 by Ben Queen from Chronicle Books)."The technology advancements help the ease of what we do, he says"

Once again, it's all about the Pixar's special confluence of storytelling and artistry.

Bill Desowitz is senior editor of AWN & VFXWorld.