J Brabyn, A Alden, G Haegerstrom-Portnoy, M Schneck
Smith-Kettlewell Eye Research Institute, San Francisco, United States
The Global Positioning System (GPS) was designed for open areas (the sea, the air, the battlefield etc) with few obstructions or reflections to degrade the satellite signals. The technology has long been agreed to be promising as a source of navigational information for blind travelers, as the generally quoted specifications could allow it to resolve detail as fine as street addresses and building entrances. However, there is little published data on its use in environments of interest to this population - particularly urban pedestrian settings. Using a state-of-the-art receiver, with and without differential correction signals, we took readings from locations including a very open, unoccluded neighborhood park, the sidewalk on a residential street, and the sidewalk on a shopping/commercial street (with 2-4 story buildings). In each case, we recorded sets of 20 readings over several weeks. Using the differential GPS signals, 90% of readings in the open park location fell within a 16-meter diameter circle centered on the mean reading. The circle diameter was 32 meters in the residential location and 60 meters in the commercial/business area. The study indicated that performance approaches the widely quoted values in open areas, but degrades considerably in close proximity to buildings and other urban features. Addition of other inputs such as dead reckoning could be used to improve navigation in real-world urban use.
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