Location Detection Principle

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 DVD-ROM, which is stored in the DVD-ROM drive (map-matching), and indicated on the screen as a current-location mark. More accurate data is judged and used by comparing vehicle position detection results found by the GPS with the result by map-matching.

  Fig 1: Identifying Navigation System Diagram

  Courtesy of NISSAN MOTOR CO., U.S.A.

The current vehicle position will be calculated by detecting the distance the vehicle moved from the previous calculation point and its direction.

• Travel distance

  Travel distance calculations are based on the vehicle speed sensor input signal. Therefore, the calculation may become incorrect as the tires wear down. To prevent this, an automatic distance correction function has been adopted.

  Fig 2: Identifying Accurate Vehicle Position

  Courtesy of NISSAN MOTOR CO., U.S.A.
• Travel direction

  Change in the travel direction of the vehicle is calculated by a gyroscope (angular velocity sensor) and a GPS antenna (GPS information). They have both advantages and disadvantages.

More accurate traveling direction is selected because priorities are set for the signals from these two devices according to the situation.