Global positioning satellites are placed in orbit above the earth's atmosphere. These systems provide a tool for labeling every point on the surface of the planet using longitudinal and latitudinal coordinates. Three satellites must be in orbit overhead, in any given region of the earth before triangulation strategies can be used to determine exact position. Almost always there are at least three overhead at any time, and most often many more. Three satellites generally provide only poor information, giving location data that has a large deviation of error. Instead of indicating an exact position, three satellites give a position that many be off by many feet. The more satellites active and accessible, the greater the accuracy.
GPS use is expanding rapidly. Vehicle fleets (taxis, trucks, trains, planes, boats) use them routinely. They are showing up as part of the standard package in passenger vehicles. Farmers use GPS to tag individual plants, and engineers, architects, travel consultants, builders, and many other professionals increasing use the technology for their own ends.
GPS location-based knowledge has two components; a coordinate system for labeling longitude and latitude, and a managed geographical data base (there are several) for getting map and landmark details. The result of this technology is that every open area on earth has gotten smarter; it contains knowledge about "itself." This knowledge is getting richer and richer as institutions add details to the geographical data bases, and as computer technology gets ever more sophisticated. Currently (2003), GPS systems are capable of providing users constant updates about their location, including the street they are walking on, the direction of travel, the speed of travel, identification of buildings being passed, and listings of intersections.
GPS systems are limited to outdoor spaces. They cannot currently be accessed from within a building. Also, in large cities buildings tend to block out satellite signals, reducing the number of available units for calculating position. This means that the system is more or less accurate as you move about metropolitan areas.
The major telecom groups are all developing technology that will eventually be wireless, and will provide services such as real time traffic reporting, menus of restaurants being passed, historical information about points of interest in the area, internet access, and so on. The adaptations nescessary to make these services blindness friendly will also evolve quickly, but at a slower pace than services to the sighted population.
A wireless prototype GPS system for the blind is under development in Europe by a Spanish Company called GMV Sistemas. It is a handheld device using satellite technology created by the European Space Agency (ESA). The unit locates pedestrian position and guides blind individuals along routes. Testing is being done by the Spanish organization O.N.C.E. ESA's GPS uses the Egnos system which is advanced technology that provides very accurate location based information. It is employed alongside a technology called SisNet which sends information through the internet using wireless units. GMV Sistemas calls it's personal navigator for the blind "Tormes." The units include a Braille Keyboard, a voice synthesizer, and a GPS receiver. The system comes with an always-on GPRS wireless internet connection.
It is an obvious step to employ GPS technology to the problem of blind navigation, especially for travel through complex outdoor environments. The leading company for GPS technology in the United States for blind individuals is Sendero Group, located in Davis, California.
A prototype GPS system has also been developed at Nottingham University in England.
In Quebec, Canada Visuaide has developed a GPS system for the blind called the VictorTrekker; the first version release is set for the first quarter of 2003.