[Source : GPS World]
Installed GPS navigation systems are becoming popular options for new car buyers. and many aftermarket, portable, and PDA- or cell phone–based systems are available in the marketplace.
A basic GPS navigation system can provide continuous, accurate navigation, except when the GPS signals are blocked by buildings, tunnels, or other obstructions or when multipath or interference reduces position accuracy. A factory-installed system might include additional sensors such as an odometer or gyroscope to provide dead-reckoning navigation when GPS signals are lacking.
Another aid to accurate navigation is map-matching in which the computed position fix is snapped onto the nearest road. However, depending on the fix error and the density of the road network, the system may or may not snap the fix onto the correct road. In this month’s column, guest authors Syed and Cannon examine a novel technique that tightly integrates information from accurate maps with raw GPS and gyro data to determine a vehicle’s position. Using classic statistical theory and fuzzy logic algorithms, the technique improved vehicle navigation accuracy in an urban canyon setting by more than 30 percent. — R.B.L.
The confluence of wireless technology and GPS has led to the development of a new set of applications to serve the location-based needs of users. These applications are popularly known as location-based services, and a major portion of the location-based services market deals with applications using in-car navigation systems. These systems supply vehicle-position information for applications to provide guidance to nearby points of interest, advise on current traffic or weather conditions, and even generate location-based advertising.
Progressive industry leaders are building solid foundations to support well-conceived solutions for new location applications and value-added services. The other strong impetus for the development of location-based services comes from the United States Federal Communications Commission’s Enhanced 911 mandate, which directs that all mobile phones be located for 67 percent of 911 calls with an accuracy of 100 meters for network-based technologies and 50 meters for handset-based technologies.
A key to the success of location-based services applications is accurate georeferencing of the position output obtained from a navigation system. Georeferencing involves relating the position to a map database to identify the road on which a vehicle is traveling. This procedure is called map matching. Systems that combine navigation and map data need the following characteristics to be effective and broadly used: affordable cost, accuracy of approximately 20 meters (at a 95-percent confidence level), automatic initialization without any input from users, effective display of position and location-based information, and a reliable map database.
In this article, we outline some of the challenges of positioning in urban areas and the problems that can occur when attempting to overlay inaccurate positions on a map. We introduce a new map-aided navigation technique, which integrates raw GPS measurements and map data, and provide some results from field tests to show the increased level of reliability when these two data types are integrated tightly.