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Reconstructing Cities in a Day

Hot on the heels of the announcement of success of an ambitious scheme to reconstruct planetary surfaces from thousands of photographs, comes news of another system, using a different method, but which can do the same thing with a city.

A new computer algorithm developed at the University of Washington uses hundreds of thousands of tourist photos to automatically reconstruct an entire city in about a day.

To prove it works, a digital copy of Rome was constructed, using precisely this method.

This example image shows the colliseum, reconstructed as a full 3D model from thousands of tourist photos. The black dots surrounding it, are the locations the tourist photos were taken from.

In total, 150,000 photos found online, and tagged as being of Rome, were used, to reconstruct large swathes of the city, including all the major landmarks.

"How to match these massive collections of images to each other was a challenge," said Sameer Agarwal, a UW acting assistant professor of computer science and engineering and lead author of a paper being presented in October at the International Conference on Computer Vision in Kyoto, Japan. Until now, he said, "even if we had all the hardware we could get our hands on and then some, a reconstruction using this many photos would take forever."

The software is an update on the freely available Microsoft Photosynth - originally developed by the same team. With a much improved AI, the new 'Photo Tourism' program, is also intended for use by home users, and creates 3D models from aggregate photos, for users to use as models in any virtual environment. Understandably of course, a single computer will take rather longer than a day.

"With Photosynth and Photo Tourism, we basically reconstruct individual landmarks. Here we're trying to reconstruct entire cities," said co-author Noah Snavely, who developed Photo Tourism as his UW doctoral work and is now an assistant professor at Cornell University.

In addition to Rome, the team recreated the Croatian coastal city of Dubrovnik, processing 60,000 images in less than 23 hours using a cluster of 350 computers, and Venice, Italy, processing 250,000 images in 65 hours using a cluster of 500 computers.

"If a city reconstruction took several months, it would be just about building Rome, but on a timeline of one day you can methodically start going through all the cities and start building models of them."



Reconstructing Whole Worlds from Photos


Rome was built in a day, with hundreds of thousands of digital photos

Building Rome in a Day

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