Creating a Virtual 3-D World: Inside PhotoCity from UW and Cornell

[Updated 3:30 pm, 4/23/10. See below] Zoran Popovic, a computer scientist at the University of Washington, is constructing 3-D virtual recreations of real life. First step, the UW campus; next, the whole world.

Building on a previous program called Photo Tourism that pieces together photos culled from Flickr into virtual 3-D models, PhotoCity is a “capture the flag”-esque game that recreates sections of campuses or city blocks, or, eventually, entire cities from user-generated photos (see reconstructed image, above right).

Photo Tourism was created by UW professor Steve Seitz, Microsoft researcher Richard Szeliski, and former UW graduate student Noah Snavely (now an assistant professor at Cornell University), and in 2006 was licensed to Microsoft. But that program was limited, Popovic said: While they could easily build a 3-D version of the Coliseum based on tourist photos deposited in Flickr, they were never going to get a usable model of the building next to the Coliseum, for example. [The list of people involved with Photo Tourism and PhotoCity has been corrected and updated—Eds.]

Popovic is interested in what he calls “serious games,” computer games that rely on volunteer user input to solve problems too difficult for computational power alone. Usually, players are motivated to help solve a problem by the lure of some kind of online competition. But recreating 3-D versions of city blocks or whole cities adds another layer of challenge—the game has to be compelling enough not only to get people to sit down and play it on their computers, but to take extra digital pictures for the sole purpose of expanding the 3-D world. “It occurred to me that one big problem is that you have to step away from the computer,” Popovic said. “So we wanted to know, is it possible to form a game framework where people go out and do stuff in the real world, instead of just sitting in front of their computers?”

To motivate people to take more pictures for the models, the group (including UW graduate students Kathleen Tuite and Dun-Yu Hsiao) created the PhotoCity game, which can be played on a computer or iPhone. A Google Maps image shows the playing field (so far, game locations include the UW and Cornell campuses, and neighborhoods in Seattle, New York, Boston, Chicago, Santa Barbara, Portland, Washington DC, and Moscow), and “flags” pop up at various points on the rough facade. Players then win these flags by taking enough pictures of that site—say, the northwest corner of UW’s Odegaard library—and then uploading them to the PhotoCity site. Win enough flags and you’ll eventually be the “owner” of the whole building. Other players can steal flags away by taking even more pictures.

Zoran Popovic

The researchers launched the game at the end of March by announcing a competition between UW and Cornell, to see which school’s team could get the most photos of their campus by April 20, but soon other locations were added. Any user can “seed” a new playing field. The cross-country competition is now over, but results are still being analyzed, Popovic said, and the teams are planning a second round to start up April 30.

Popovic (left) is happy with how the game has progressed, but his group’s eventual goal is loftier: to recreate entire cities and, eventually, the world in 3-D from digital pictures. “If you can build a 3-D replica of your world, you can all of a sudden have all different kinds of games in that world,” Popovic said. “The idea is to make a game where the actual world itself is built, and people can actually become avatars and walk around and do … Next Page »

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Rachel Tompa is a freelance journalist based in Seattle. She can be reached at [email protected] Follow @

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