Wednesday, August 16, 2006

Seeing by Sound

A new wearable computer can transform cities and buildings into soundscapes, researchers say, helping visually impaired people get around more easily.

By Susan Nasr

Researchers Frank Dellaert (left) and Bruce Walker (right) hold a GPS and computer vision system for guiding people with blindness. Dellaert holds two versions of the hat-mounted cameras that function as the system’s "eyes" during navigation indoors. (Credit: Rob Felt, Georgia Institute of Technology)

Blind people traversing a city face a formidable challenge: quickly and safely navigating a complex environment. Researchers at the Georgia Institute of Technology say their wearable computer provides the newest high-tech solution.

The system's hardware includes two Global Positioning System (GPS) receivers, a laptop, head and body compasses, a gyroscope-based tracker that measures the head's tilt, and four small cameras mounted on a helmet. For audio (the device uses a speech interface), users listen to "bone phones," which fit behind the ears and transmit sound by vibrating against the skull. A user's ears are thus free to listen to important ambient noise, such as city traffic. It weighs about three pounds in total, and most parts tuck neatly into a backpack.

The device uses GPS and digital maps to guide the wearer to a destination. Outdoors, GPS pinpoints a user's location. Users verbally tell the device where they want to go, and the system wirelessly extracts an area map, which includes everything from businesses to bushes, from a remote Geographic Information System (GIS) database. Then, "sound beacons," soft tones emanating in stereo through the bone phones, guide the person to a destination.

"Imagine there's a ring around your head a meter away from your body," explains Bruce Walker, assistant professor of psychology and designer of the auditory interface. "If you need to walk straight, the sound will come from straight ahead. If you need to turn a corner, the sound will seem to come from the right. Turn your body until the sound is in front of you again -- and away you go." And the tones speed up as users approach their destination.

The navigation is precise without requiring bulky antennas, the researchers say. By combining data from multiple GPS receivers and other location sensors, then accounting for error in the devices' estimates, the system pinpoints users' locations much more accurately than GPS alone, to within a foot of where they really are.

Although GPS loses a signal indoors and between tall buildings, the cameras, which are part of a computer vision system, pick up the slack. "By having computer vision on board, we can go where GPS can't," says Frank Dellaert, assistant professor of computing at Georgia Tech. Indoors, the cameras "see" building interiors in lines and patches of color. The computer searches stored building floorplans for these shapes, finally pinpointing the user's location, by matching the cameras' input to a location on a digitized floor plan of the building. Sound beacons then guide users as they do outside.