Principle Of Operation
The Global Positioning System is a satellite based system developed by the US Department of Defense that provides both military and civilian users accurate information about location.
The GPS system uses 24 satellites in six orbits 12,550 miles above the Earth moving at 1.7mi per second. Usually 7 to 10 satellites are in view over any one point on the earth.
The GPS satellites are basically extremely accurate clocks that broadcast a coded signal representing time. The GPS receiver determines it's distance from the satellite by measuring the time it takes between satellite transmission of the signal and reception to the receiver. The receiver does this with at least 2 other satellites and uses the information to determine the vehicles latitude, longitude, and altitude. The accuracy of the system for civilian use is within 100m (300ft).
The vehicle must have an unobstructed view of the sky to receive the maximum amount of satellite signals. Trees, large buildings and excessive cloud cover can block the reception of the satellites' transmissions.
The GPS antenna passes the signal to the GPS receiver incorporated in the navigation computer. A CD with map data is loaded in the CD drive of the navigation computer. The navigation computer combines the vehicle position calculated by the GPS with this map data.
The current position of the vehicle can be shown on the on-board monitor by selecting "Emergency" from the main menu.
The driver can enter a destination. The navigation computer calculates a route from the current location to this destination based on selectable criteria (main use of highways, shortest distance, etc.). The calculated route is shown in the route display.
The navigation computer generates the RGB color video signal for all on-board monitor displays. These three signals are sent over separate shielded wires to the on-board monitor.
In the case of the E52 MIR (also referred as radio navigation) which does not have a color display, the visual display data is sent via one wire called the navigation bus. On both systems, color and monochrome display, the audio output from the navigation computer for voice directions is sent over two separate wires.
The driver has the choice of displays that utilize a color map with an icon of the vehicle being traced on the map or the use of arrow indicators and distance data shown on the on-board monitor display. Vehicles equipped with the wide screen board monitor have a split screen option that includes both display methods. The MIR only makes use of the arrows and distance display. With the assistance of voice prompts, the navigation computer indicates how and where to get into the correct lane or turn off.
The navigation computer calculates the distance traveled from the wheel speed signal delivered by the DSC control unit.
The gyro incorporated into the navigation computer housing informs the navigation computer when the vehicle is turning. An alternative route is re-calculated automatically if the driver does not follow the original route instructions.
Once the driver has reached their destination, the navigation computer is ready for another destination input.
Refer to the on-board monitor owners manual for instructions on using the navigation system software.