Principles Of Operation: Notes

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The system used to calculate the current position of the vehicle is called the GPS (global positioning system) . The system utilizes satellites which are owned by the United States Department of Defense (DoD). A total of 24 satellites orbit the earth every 12 hours at a height of 20,000 km (12500 miles), and between 5 and 11 of these satellites can be seen from a single point at any given time. The orbits are tilted to the earth's equator by 55 degrees to ensure coverage of polar regions. Each satellite transmits radio signals to provide information about the satellite position i.e. latitude, longitude, altitude, almanac data and an accurate time signal generated by an on-board atomic clock. Each satellite contains four atomic clocks.

The vehicle needs to receive data from at least four different satellites to give a three dimensional fix on its current position.

As the vehicle moves, this information is continually being updated. The computer determines which satellites are 'visible' to the system and their current position and relationship to each other. Using this information the computer can account for positional deviations of the satellites and compensate to enhance the accuracy of the navigation system.

The GPS (global positioning system) signal is also known as the Precision Positioning Signal (PPS).

PPS predictable accuracy is:

22 meters horizontal accuracy
27.7 meters vertical accuracy
200 nanoseconds time accuracy.

The navigation system provides computer generated audible and visual route guidance information to enable the driver to reach a desired destination. The system allows the driver to choose the desired route using minor or major roads or highways and the quickest or shortest route. Directions to hospitals, museums, monuments and hotels are also available. The computer uses map information stored on a DVD-ROM to determine the best route for the journey and provide the driver with details of directions and approaching junctions.

The navigation system receives GPS (global positioning system) information via the GPS antenna. The GPS signals are used by the navigation computer to calculate the vehicles position. Once the driver has input a desired destination the navigation computer can calculate a route, based on the drivers pre-determined preferences or the default settings in the navigation computer.

The navigation system is accessed by pressing the navigation soft key on the TSD.

Navigation is initiated by the driver inputting a destination. This can be achieved by:

Entering in an address using the TSD.
Entering a post code.
Choosing a previous destination.
Choosing a point of interest from the map disc database.
Choosing the home location
Choosing a memory stored location.

The driver is then guided to the destination by a scrolling map display and voice guidance. The display can be varied by scale and display type.

In addition to the standard navigation system there are two market dependent systems that supply extra information to the navigation system and the driver. These are:

Traffic Message Channel (TMC)
Vehicle Information and Communication System (VICS) (Japan only).