Position Detection Principle

The navigation system periodically calculates the current vehicle position according to the following three types of signals.

• Travel distance of the vehicle as determined by the vehicle speed sensor
• Vehicle turning angle determined by the gyroscope (angular speed sensor)
• The travel direction of the vehicle 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, which is stored in the HDD (Hard Disk Drive) (map-matching), and indicated on the screen with a current location mark. More accurate data is used by comparing position detection results from GPS to the map-matching.

Fig 1: Identifying Navigation System Signals

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

The current position is calculated by detecting the travel distance from the previous calculation point, and its direction change.

• Travel distance

  The travel distance is generated from the vehicle speed sensor input signal. The automatic distance correction function is adopted for preventing a miss-detection of the travel distance because of tire wear etc.

• Travel direction

  The gyroscope (angular velocity sensor) and GPS antenna (GPS information) generate the change of the travel direction. Both have advantages and disadvantages as per the following descriptions.

  Fig 2: Current Position Calculation Diagram

  Courtesy of NISSAN MOTOR CO., U.S.A.
  GYROSCOPE (ANGULAR VELOCITY SENSOR) AND GPS ANTENNA ADVANTAGES AND DISADVANTAGES
  
  

  Type	Advantage	Disadvantage
  Gyroscope (angular velocity sensor)	The turning angle is precisely detected.	Errors are accumulated when driving a long distance without stopping.
  GPS antenna (GPS information)	The travel direction (North/South/East/West) is detected.	The travel direction is not precisely detected when driving slowly.

  Input signals are prioritized in each situation. However, this order of priority may change in accordance with more detailed travel conditions so that the travel direction is detected more accurately.