Researchers at the University of Washington are taking photo-stitching -- the "photo tourism" technology behind Microsoft's cool Photosynth service -- to the next level, using it to scour public photos and build 3-D models of entire cities.

Photosynth does the same thing for buildings or landmarks -- assembling Flickr images of Trevi Fountain to build a 3-D rendering that can be explored from different angles. It was developed at the UW and licensed to Microsoft in 2006.

Today the UW is calling out the work, by Sameer Agarwal, an acting professor of computer science, and Noah Snavely, who worked on photo tourism as a UW doctoral student and now teaches at Cornell University.

In one example, they used all 58,000 images of Dubrovnik on Flickr to build a model, which took five hours using 352 compute cores.

"With Photosynth and Photo Tourism, we basically reconstruct individual landmarks. Here we're trying to reconstruct entire cities," Snavely said in the release.

Agarwal was lead author of a paper on the project being presented at the International Conference on Computer Vision in Kyoto, Japan, next month.

Check out the videos. I wonder if this is how Earth will appear to alien robots if they invade our planet someday.