August 2009 Theme:
Cloud Computing: Opportunities and Challenges
Guest Editors' Introduction by Norman I. Badler and Carol O’Sullivan

The boundaries between the real and virtual worlds are breaking down: computer-generated (CG) characters and scenes in movies engage and convince us, and our kids are as comfortable interacting with graphical environments and characters as they are with their own real-world friends and families. This trend is not only true in the interactive entertainment arena, but it extends into the realms of business, politics, education, and beyond. In this Computing Now special issue, which serves as a companion piece to our July special issue on Virtual Populace in IEEE Computer Graphics & Applications (CG&A), we present six articles (two from the special issue and four on related topics) that give a flavor of current research in this exciting area—we hope you enjoy them.

In “3D Social Worlds: Research Issues and Challenges,” (login required for full text) Adel Hendaoui, Moez Limayem, and Craig W. Thompson explore virtual worlds’ potential applications and some of the many issues that they raise, such as social, educational, political, and ethical considerations. With such a dramatic increase in the importance and ubiquity of virtual worlds in our everyday lives, it’s clear that many technological challenges remain to be tackled. Hendauoi and his colleagues highlight some of them, such as standards for communication and 3D protocols, display technology, software design, accounting, and security issues. Natural modes of interaction with virtual environments and characters are also worthy of attention, with new research even going so far as to developing interfaces that are controlled directly by the human brain, as Anatole Lécuyer and his colleagues describe in their article “Brain-Computer Interfaces, Virtual Reality, and Videogames.” (login required for full text) They describe how people can perform tasks such as navigation and object manipulation through cerebral activity alone. For example, researchers in Graz University of Technology and University College London conducted an experiment in which a tetraplegic person was able to navigate through a virtual street populated with virtual pedestrians by imagining the movements of his feet as he moved from one virtual character to another. Such research demonstrates the power of virtual worlds to enable new discoveries in other fields, such as neuroscience, to amplify and extend human capabilities, and to be truly open and inclusive for all types of users.

For computer graphics developers and researchers, building and visualizing realistic, large-scale virtual environments is a very active area, as evidenced by the articles in the recent CG&A special issue on Procedural Methods for Urban Modeling. Ben Watson and his colleagues’ article “Procedural Urban Modeling in Practice” (login required for full text) provides the background to synthesizing urban terrain and buildings. They describe how practitioners can fit procedural modeling to various industry processes, such as movie pre- and post-production, game development workflow, and cultural heritage applications. They also point out how important people are for such simulated cities, as without people they are simply empty “ghost towns.” Furthermore, we can use virtual cities to simulate reactions to potentially dangerous situations, as Nuria Pelechano and Norman Badler describe in their article “Modeling Crowd and Trained Leader Behavior during Building Evacuation.” Here, animated agents, with roles such as trained personnel, leaders, and followers flee a complex building using simple navigation strategies and communicating shared knowledge.

Virtual populace is therefore a vital element that breathes life into virtual worlds—be they the relatively simple representations of real people (for example, avatars) in online social worlds or computer-controlled intelligent agents (nonplayer characters) in the gaming world. We’ve seen perhaps the best examples of CG crowds in recent years in movies. In the special issue article “Brain Springs: Fast Physics for Large Crowds in WALL•E,” (login required for full text) Paul Kanyuk describes how Pixar animated crowds of robots and humans in the recent popular movie. Finally, Christopher Peters and Cathy Ennis discuss how to ensure that virtual populace simulations actually meet a viewer’s expectations of how people behave in the real world. In their article “Modeling Groups of Plausible Virtual Pedestrians,” (login required for full text) they describe a methodology that uses information extracted from video and a set of perceptual experiments to determine what is most important when simulating small groups of people within a crowded area.

The computer graphics community is actively developing the technologies and software tools needed to create applications that require populated virtual worlds. The existence of virtual beings in these environments creates depth of experience and social presence for a user. We’re at the edge of a new frontier.

We hope you enjoy this Computing Now theme on virtual worlds.

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Guest Editors

Norman I. Badler is a professor of computer and information science at the University of Pennsylvania. He also directs the university’s SIG (Susquehanna International Group) Center for Computer Graphics, which includes the Center for Human Modeling and Simulation. His research interests include animation by simulation, embodied-agent software, human-computer interfaces, and computational connections between language and action. Badler has a PhD in computer science from the University of Toronto. He’s coeditor of Graphical Models, and he cochaired the 2004 Symposium on Computer Animation. Contact him at

Carol O’Sullivan is an associate professor at Trinity College Dublin. Her research interests include perception, animation, virtual humans, and crowds. O’Sullivan has a PhD in computer graphics from Trinity College Dublin. She’s the program cochair of the 2009 Siggraph Symposium on Applied Perception in Graphics and Visualization, co-editor in chief of ACM Transactions on Applied Perception, and an editorial board member of IEEE Computer Graphics and Applications. Contact her at