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Research paper : How car navigation systems have been put into practical use (H. Ikeda et al.)−281−Synthesiology - English edition Vol.3 No.4 (2011) traffic jams. To make the system practical, it was necessary to provide both onboard equipment and an infrastructure. The system was not practical, with development caught in the dilemma of chicken and eggs. However, its usefulness was proven in guiding vehicles to uncrowded roads using traffic information.Aside from this, the National Police Agency was promoting a patrol car location system[4] (car locator in police terminology) development project to enable the control center to recognize locations of patrol cars and guide them so that the patrol cars could be deployed efficiently.In these circumstances, already involved in road infrastructure technology, Sumitomo Electric felt the need to develop a NAVS. In 1983, having taken the initiative in traffic management and CACS projects at Sumitomo Electric, Nobuo Yumoto (later Senior Managing Director) found map-matching that was being developed in the US, and realized if it could be incorporated into the NAVS, the system could be made practical. He then began developing a NAVS employing the map-matching system. Subsequently, the government and the private sector collaborated to develop the technology for the Road and Automobile Information System. In 1984, the Road /Automobile Communication System (RACS) started operation and in 1987, the Advanced Mobile and Traffic Information Communication System (AMTICS) commenced. These systems facilitated acquisition of vehicle information. Meanwhile the NAVS began to be installed in vehicles. There was a growing trend toward introducing a new vehicle information system for mobile units. Consequently, existing members of AMTICS and RACS plus new members established Vehicle Information and Communication System (VICS) in 1991, which later evolved into the Intelligent Transportation System (ITS).3 Navigation system developmentIn its development of the NAVS, which consisted of an onboard NAVS and a patrol car locator, Sumitomo Electric developed common technology and parts for both. This report focuses on the NAVS.3.1 Current location detection technologies(1) Technological development of map-matching[5]The basic technologies for the NAVS are: location detection to determine where the vehicle is, and route computation to calculate the route to the destination and guidance to guide the vehicle along the route.Location detection, one of the basic technologies, is relatively easy using the GPS satellite-based system. In the early days of our development of the patrol car locator and NAVS, there existed only a few GPS satellites. Moreover, the GPS satellites were still under construction and were not fully usable, being available for only one to two hours a day for location calculations.1) Development of map-matchingIn principle it is possible to identify the current location if the original location, driving distance from that location and driving directions are known. This method is known as dead reckoning. One critical factor in dead reckoning is the accuracy of the sensors used to detect driving distance and directions. Although highly accurate and highly expensive sensors were used in submarines and aircraft, it was not cost effective to use them in automobiles. US-based Etak developed a method to achieve correct location detection without expensive sensors. This method was map-matching which, assuming that the vehicle moves on roads, compares the vehicle’s trajectory detected via dead reckoning with a map and corrects the errors, thereby minimizing cumulative errors produced by the sensors and detecting the correct location. Figure 1 shows a schematic for illustrative purposes.The blue line represents the dead reckoning-based trajectory. Slight deviations in driving distance and direction result in a gradually accumulating error from the true location on the road indicated with the green line. When the vehicle makes a turn at an intersection, map-matching accesses road map data to search for the location of the intersection and corrects the vehicle’s current location to the intersection location.The red line represents the corrected trajectory based on map-matching. The trajectory is corrected to be on the road, which reassures the driver. Sumitomo Electric pondered whether or not to adopt Etak’s technology. Differences concerning road density and road configuration between Japan and the United States and other substantial discrepancies that would affect the logic, as well as prospects for future development, made the company develop the required technology in-house.Fig. 1 Principle of map-matching (Courtesy: Sumitomo Electric Industries, Ltd.)Estimated trajectory based on map-matchingEstimated trajectory based solely on sensorsActual trajectoryRoadError③②①③②①

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