To begin, an AR system needs to know two things precisely: where you are located, and where you are looking. In order to accurately superimpose data in the field of view, the MARS system relies on two separate inputs: data from the differential Global Positioning System (GPS), which helps determine within centimeters the spot where you're standing, and data from equipment that calculates the direction of vision, down to a few degrees' accuracy. For positioning, the system triangulates signals from several GPS satellites overhead -- hence the flying-saucer antenna -- and a GPS transmitter on Columbia's engineering building. For orientation, an inertial/magnetic tracker rides on a headband above the AR glasses. This device is a combination of miniature gyroscopes and accelerometers that detect head movements along with an electronic compass that establishes the direction of the viewer's gaze in relation to Earth's magnetic field.
What's the critical factor here? "Registration, registration, registration," say AR researchers, echoing the old real estate mantra. The challenge is to accurately and continuously determine the line of sight and then align the graphics to it. Getting around the registration roadblock is less of a problem indoors, where tiny video cameras in a head-worn tracker can relatively easily read orientation and positioning bar codes or flashing infrared markers placed on a ceiling. Outdoors, however, the situation gets much more dicey. Because the tracking system currently used is sensitive to sudden variations in magnetic fields, the alignment of graphics and a street scene can be easily thrown off by even a stray remnant of 19th century technology like old iron trolley car tracks beneath asphalt. Ultimately, resolving registration difficulties may require the addition of computer vision analysis systems, with sophisticated software that can recognize the video outlines of rooms or buildings and match them to stored 3-D computer models of the real world.
Still, even if this is overcome, there will have to be a leap forward in wearable computer technology as well. During the past few years, more convenient brick-size, wearable PCs have been marketed by a number of small firms. The most prominent is Xybernaut Corp., which is selling the U.S. version of Hitachi's Wearable Internet Appliance, known as the Poma -- the first wearable computer to be sold to businesses and consumers through office supply stores and electronics retailers. Essentially a Pocket PC with a color head-worn (single-eye) display, it bears the slim profile of what researchers envision will characterize an AR appliance of the future. But despite its tricked-out design, this device is only as powerful as a typical PDA and far too limited for stereoscopic 3-D position-sensitive AR. The top AR researchers -- Steven Feiner, the developer of MARS at Columbia, and his counterparts at the University of North Carolina, Georgia Tech, and the University of Washington, along with researchers at companies such as Sony and Siemens -- estimate that it will take at least two more years before an AR-capable wearable computer will be developed.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.