|
|
AV-140 < SYSTEM DESCRIPTION > [NAVIGATION] SYSTEM The navigation system periodically calculates the vehicle's current position according to the following three signals: • Travel distance of the vehicle as determined by the vehicle speed sensor • Turning angle of the vehicle as determined by the gyroscope (angular velocity sensor) • Direction of vehicle travel as determined by the GPS antenna (GPS information) The current position of the vehicle is then identified by comparing the calculated vehicle position with map data read from the map SD-card (map-matching), and indicated on the screen as a vehicle mark. More accurate data is judged and used by comparing vehicle position detection results found by the GPS with the result by map-matching. The current vehicle position will be calculated by detecting the dis- tance the vehicle moved from the previous calculation point and its direction. • Travel distance Travel distance calculations are based on the vehicle speed sen- sor input signal. Therefore, the calculation may become incorrect as the tires wear down. To prevent this, an automatic distance cor- rection function has been adopted. • Travel direction Change in the travel direction of the vehicle is calculated by a gyro- scope (angular velocity sensor) and a GPS antenna (GPS informa- tion). They have both advantages and disadvantages. More accurate traveling direction is detected because priorities are set for the signals from these two devices according to the situation. MAP-MATCHING Map-matching compares a current location detected by the method in the “Location Detection Principle” with a road map data from map SD-card. NOTE: The road map data is based on data stored in the map SD-card. The vehicle position may not be corrected under the following circumstances and after driving for a certain time when GPS information is difficult to receive. In this case, the vehicle mark on the display must be cor- rected manually. • In map-matching, alternative routes to reach the destination will be shown and prioritized, after the road on which the vehicle is cur- rently driven has been judged and the vehicle mark has been repo- sitioned. Alternative routes will be shown in different order of priority, and the incorrect road can be avoided if there is an error in distance and/or direction. Routes are of the same priority if two roads are running in parallel. Therefore, the vehicle mark may appear on either of them alter- nately, depending on maneuvering of the steering wheel and con- figuration of the road. SEL684V Type Advantage Disadvantage Gyroscope Can detect the vehicle's turning angle quite Direction errors may accumulate when vehicle is GPS antenna Can detect the vehicle's travel direction Correct direction cannot be detected when vehicle SEL685V SEL686V |