Position 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 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 distance the vehicle moved from the previous calculation point and its direction.

Fig 1: Current Vehicle Position

Courtesy of NISSAN NORTH AMERICA, INC.

• 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.

• 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.

  Type	Advantage	Disadvantage
  Gyroscope (angular velocity sensor)	Can detect the vehicle's turning angle quite accurately.	Direction errors may accumulate when vehicle is driven for long distances without stopping.
  GPS antenna (GPS information)	Can detect the vehicle's travel direction (North/South/East/West).	Correct direction cannot be detected when vehicle speed is low.

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