Forget GPS and streaming video — future legions of city-dwelling robots may navigate using manhole covers.

The ubiquitous round metallic covers each have different shapes and sizes, occasionally for the sake of aesthetics and certainly when you account for wear and tear. In Japan, manhole covers are frequently works of art reflecting something about their cities. And every city has them — they’re one of the more permanent, reliable fixtures of the built environment, as New Scientist points out.

Hajime Fujii and colleagues from Shibaura Institute of Technology in Tokyo say robots could take advantage of this and use the covers to estimate their positions. All you would need is a basic metal detector attached to a robot’s foot.

Other robot-navigation methods use GPS, laser-range scans and even CCD cameras that compare a robot’s view to maps or even Google Street View. But environmental factors can skew the data from these sources, Fujii writes — GPS isn’t always reliable in cities, and Street View may not be so not helpful at night. Maps are helpful, but robots would still need to check their position against some kind of environmental landmark.

In Fujii’s system, it’s as simple as manhole covers. Every cover would be scanned and its shape would be entered into a database for each city. Robots would be able to find the covers using a metal detector, and swipe some kind of scanner across the covers to cross-check the database and figure out where they are.

Of course, this would require robots stepping into traffic to check their whereabouts. But when we all have flying cars, that won’t matter!

New Scientist