CityEngine Revs Up Urban Modeling

12 Aug, 2008 By: Heather Livingston

Procedure-based program enables users to define the rules of how a building should look and then apply those rules.

In July, the Swiss company Procedural officially released CityEngine, a procedure-based 3D city creation system capable of generating large urban environments 10 times faster than previous solutions, according to the company. Although the concept was revealed at SIGGRAPH 2006 and select projects already have enlisted the program, this is the first time CityEngine has been available to the general public. Among its early clients, the University of Virginia currently is using CityEngine to generate architectural elements for the world's largest virtual reconstruction project, Rome Reborn.

Located in Zurich, Procedural is the creation of founder and CEO Pascal Müller. A former researcher at ETH Zurich (also commonly known as the Swiss Federal Institute of Technology), Müller began exploring the field of procedural urban modeling while working on his master's thesis at ETH and further refined it with his series of SIGGRAPH publications. The SIGGRAPH papers in turn guided the creation of CityEngine, Procedural's flagship product. Led by chief technology officer Simon Schubiger, the Procedural team transformed Müller's research into a powerful application for use by the design, film, and gaming industries.

"Cities are huge, richly detailed artifacts that are often required in digital productions, and modeling them with existing tools can take many years," said Müller. " CityEngine addresses these previously unsolved modeling problems by offering several procedural modeling tools for generating large scale urban layouts, as well as a unique shape grammar for the efficient creation of detailed building models. With these tools, users not only experience a faster modeling experience, but one that allows them to create cityscapes that have never been seen before."

CityEngine's shape grammar was designed specifically for the rule-based production of highly detailed architectural content. With the CityEngine program, users can define the rules of how a building should look and then apply those rules, the result being a parametric building model that is created in an implicit way. This gives users the ability to drag and drop a building style and then modify its parameters, or to randomize the parameters allowing for mass variation on a city scale.

Click for larger image CEO Pascal Müller began working on the Pompeii digital re-creation while still in college at Zurich's EKH. (Click image for larger version)

Click for larger image This imagined city in the Middle East was created using CityEngine's rule-based randomized parameters which allow designers to easily introduce degrees of variation on a city scale. (Click image for larger version)

"I think one of the advantages of CityEngine is that you can model very high-res models or low-res models for a Web application or previsualization, for example," Müller said. One of our first clients [bought] the CityEngine tool for the Olympic games in 2012. After the games in London are over, they'll have to rebuild. So they're now using CityEngine to lay out simple plans, simple visualizations, different street networks, and different massings of buildings, [then] evaluate the performance of these massings. They can lay out such a thing in about one to two days, and they can create lots of variations in one to two days."

Müller said many of the queries they receive from architectural studios concern such city planning. To allow the greatest flexibility and compatibility, the procedurally generated 3D buildings can be exported in various file formats. In addition, the underlying procedural approach ensures the reusability of designs and is well suited for collaborative work environments, such as the Rome Reborn project.

Rome Reborn
Both a virtual and physical model, the Rome Reborn project was conceived to "spatialize and present information and theories about how the city looked [on June 21, 320 A.D.], which was more or less the height of its development as the capital of the Roman Empire."

Click for larger image This screen shot from the Rome Reborn project shows how rule-based modeling allows designers to create large digital cities with great efficiency. (Click image for larger version)

"CityEngine is a perfect match for the Rome Reborn project," said Bernard Frischer, director of Rome Reborn at the Institute for Advanced Technology in the Humanities at the University of Virginia. "Our project involves the complete virtual reconstruction of the city at its zenith under Emperor Constantine, when it had about one million residents. To build by hand the corresponding 7,000 apartment buildings, family houses, public buildings, and temples would have taken us forever; but CityEngine's power and flexibility made the process amazingly quick without sacrificing detail or quality. This allowed us to concentrate on modeling the unique monuments. The CityEngine also helps to quickly change the model as new scholarship or discoveries warrant."

"The good thing [about] the procedural approach is that you always can change things without losing anything you have done before," Müller elaborated. "So, for a typical application example, you have modeled a building design in a very, very detailed way, and then afterwards the art director or project director changes the massing of the whole thing and suddenly decides that now the skyscrapers have to be bigger. In the procedural approach, you just have to change one parameter and the skyscrapers are bigger. The whole detail is still there. Everything is correct. The procedural modeling approach is really that you have a very flexible model, which you can change after two days or after one month.

"After the Rome building designs had been specified in the CityEngine, generating and exporting the entire city model took exactly one hour and 55 minutes. Thus, Rome actually was built in one day — or, at least its digital counterpart was," joked Müller.

While it takes longer to model detailed structures, Müller says that it is possible to accurately model an entire city in "about three to four weeks." The Rome Reborn model was revealed this week at SIGGRAPH 2008 in Los Angeles.

Click for larger image An aerial of modern-day Venice created with CityEngine. (Click image for larger version)

Although Procedural has only recently released CityEngine, the company is not resting on its laurels. Müller said that in preparing for the next iteration, his team will focus more on energy concerns in urban planning. "There are no [energy] simulation tools [for] mid-scale or large-scale city designing [software] available, so these are things on which we are really concentrating," he added. The company hopes soon to offer a simulation tool for daylighting, reducing carbon dioxide emissions, and addressing other energy issues on a city scale. "Our goal really is to see the CityEngine as a tool for visualizing your ideas fast," Müller said.

To read more about the Rome Reborn project, visit and

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