GF82.61-P-2004TXU Position Finding and Navigation

GF82.61-P-2004TXU Position Finding And Navigation
- with CODE (530) COMAND APS USA (with navigation system)















"Continuous position finding" function
Continuous location finding means that the current position of the vehicle is calculated. It is active when the ignition is switched on circuit 15R ON) and is performed by the navigation processor N41/1). During the switch-on phase (software is loaded), only the basic position finding is available. After switching the ignition off circuit 15 OFF), all important positioning parameters are stored for the duration of the run-on time (approx. 30 min.). Once the run-on time has ended, the COMAND operating, display and control unit A40/3) switches itself off completely.

Following final execution in the destination-oriented navigation (destination reached), the position map is once again shown on the liquid crystal display (LCD).

Continuous position finding uses 3 methods, which mutually complement each other and therefore ensure very accurate and reliable position finding: These are:
^ Basic location finding (dead reckoning)
^ GPS location finding
^ Map-based position finding

Manual entry of vehicle location
It is possible to enter the location manually on the COMAND operating, display and control unit in the "Navigation" menu. This may be useful in the following cases:
^ following transport of the vehicle (e.g. ferry or train)
^ if no GPS reception is available at the start of the journey.







"Basic position finding", function
Basic location finding (dead reckoning) is the basic function of continuous location finding. It is carried out continuously by the navigation processor when the ignition is on, and is independent of the map shown on the LCD color display. The current position is stored after the ignition is switched off.

The following information is calculated with the aid of basic position finding (composite positioning):
^ Distance traveled
^ Direction of motion (forward or reverse).
^ Vehicle orientation

The basic position finding (composite positioning) is performed approximately every 1/s.

Distance traveled
The navigation processor receives the wheel speed signals from the ESP control unit (N47-5) via the Controller Area Network bus Class C (engine compartment) (CAN-C) . These wheel speed signals are evaluated to determine the distance traveled.

Direction of travel
The signal for the wheel direction of rotation, which is sent by the ESP control unit and forwarded by the central gateway control unit (N93) to the Controller Area Network bus Class B (interior) (CAN B), enables the navigation processor to detect the direction of travel (forwards or backwards).

Vehicle orientation
From the yaw rate sensor (gyro sensor) data and the sequence of locations calculated with GPS the navigation processor calculates the alignment (compass direction) of the vehicle.

The difference in the calculated mileage and the mileage actually covered between 2 turnoff points is used to automatically recalibrate the tire circumference (necessary due to tire wear).

Position finding errors during basic position finding (composite positioning)
Rolling backwards without the transmission being shifted into reverse gear is evaluated as moving forwards and can lead to temporary errors in location finding. Rolling when the ignition is switched off or transporting the vehicle can also distort the position finding.
In both cases, this deviation is automatically corrected by the navigation processor on receipt of GPS data.

The driving direction signal (forwards or backwards) is generated by the wheel speed sensors. This makes possible an exact recording of the distance traveled.

Calibration
Wheel calibration is necessary following a tire change. To do this, the input of tire size and the coding, whether new tires (depth of tread approx. 5 to 10 mm) or worn tires (depth of tread approx. 3 to 5 mm) have been fitted, is necessary. Entry of the data is performed using STAR DIAGNOSIS or on the COMAND operating, display and control unit itself. A special calibration drive is not required.







"Position finding by GPS", function
The GPS is a satellite-assisted localizing system that has been set up by the American Ministry of Defense. It is a toll-free service available throughout the world. Various GPS satellites constantly transmit time and position data. 4 satellites are needed for the first position calculation, then 3 receivable satellites are sufficient. GPS position finding is irreplaceable for journeys outside the digitized map area and after vehicle transport (e.g. train or ferry journeys and towing) A restarting of GPS localization (following interruption of satellite reception) may take several minutes (during initial startup up to 20 min.).

Every minute, approximately 50 GPS recalculations of the location take place.

The navigation processor calculates the location of the vehicle using the satellite signals received and amplified by the GPS antenna (A2/49a2).

The actual calculation is based on the measurement of the transmission times of the signals transmitted synchronously by the various satellites. Here, an important prerequisite is that the satellite and receiver clocks are synchronized. For this purpose, the receiver has an automatic time correction feature which again is possible with the aid of the satellite signals. When the navigation processor determines that the basic position finding is less precise than GPS position finding, the current calculated position is corrected with the aid of the GPS data. In addition, the vehicle's course of travel is determined with the aid of the sequence of the locations calculated with GPS.

Possible interference when receiving GPS signals
As GPS operates in the Gigahertz (GHz) range (microwaves) and the signals are weak, reception interference may occur as a consequence of the following events:

^ atmospheric interference,
e.g. bad weather, water vapor, fog
^ Multiple reception due to reflection of the signals,
e.g. from walls of buildings
^ Signal shading,
e.g. in built-up areas, in tunnels, through higher buildings, trees

GPS reception therefore necessitates a clear view of the sky. Positioning accuracy is approx. 10 m.







Function "Map-based position finding"
The position of the vehicle is constantly tracked on the digital versatile disk (DVD) map by the navigation processor. In the event of deviations in the course traveled from the calculated route, the position coordinates of the basic location finding (dead reckoning) are corrected. Map-based position finding is only available in the digitized area of the DVD map. By comparison with the calculated position of the vehicle with the DVD map, the deviation can be recognized and corrected automatically.

Function "Route calculation"
After entering the destination on the COMAND operating, display and control unit, the route is calculated and constantly updated by the navigation processor. This can only be calculated within the digitalized map areas. The calculated route is the prerequisite of the destination guidance system.

The navigation processor calculates the route using the DVD map data, corresponding destination as entered and the current position. For calculation it takes into account roads and attributes read from the DVD map, such as one-way streets, turn prohibitions, road classes, etc. (where available). Here, it is possible for the user to indicate how the route should be calculated:
^ Fastest route
^ Own selection

Under "Own selection", the following stretches can be blocked from the route calculation:
^ Freeway
^ Ferry
^ Toll routes
^ Tunnel

Toll routes are highlighted in color on the map.

Following the calculation of the route, the navigation processor generates a list of roads and junctions to be driven along. This route list is used for destination guidance. It may also be displayed by calling up the "Information" menu.

Route updating
When the driver deviates from the calculated route, a new route list is calculated by the navigation processor. When doing so, the current position and the direction of travel are taken into consideration. A "New Route" message is shown on the LCD color display of the COMAND operating, display and control unit and the instrument cluster (A1) displays "NEW RTE".

Trips outside the digitized map area
If the vehicle leaves the digitized DVD map area (e.g. driving into a multilevel car park), then no route can be calculated or updated. "OFF ROAD" appears on the LCD display of the COMAND operating, display and control unit.

Upon leaving the map boundary (e.g. foreign country), the message "OFF MAP" appears. Destinations which lie outside of the digitalized map area cannot be taken into consideration on calculation of the route.

Bypassing traffic tailbacks through the "Detour" function
After a tailback message via traffic radio and before the route section concerned is reached, a route calculation can be arranged which bypasses the tailback. To do this, the user must press the "Bypass" button and enter the following data:
^ The length of the traffic jam, including the distance to the start of the traffic jam
^ The corresponding stretch must be blocked within the detailed route list.







"Route guidance" function
Destination guidance is the generation and output of driving recommendations, in order to guide the driver to the desired destination. The prerequisites of destination guidance include:
^ Continuous position finding in operation (takes place automatically).
^ Destination was entered
^ The route has been calculated.

The navigation processor constantly compares the route calculation data with the continuous position finding data.The measures for further route guidance are derived from this. Depending on the position of the vehicle, a distinction can be made between the following 2 destination-oriented navigation modes:
^ Navigation within the digitized DVD map area
^ Destination-oriented navigation in non-digitized map area

"Destination-oriented navigation in digitized map area" function
On journeys within the digitized map area, the following information, calculated by the navigation computer, is available to the user:
^ Current position and route of vehicle on digitized map
^ Route list
^ Distance from the destination and likely time up to arrival
^ Direction recommendation
^ Direction indication arrow
^ Name of the road currently being traveled along
^ Name of the road to turn into
^ Distance from the next junction (specified in units of length or as a bar graph)

For destination guidance, 3 illustration modes are possible:
^ with map
^ with map and symbol display before turn-off points
^ with symbol display (guide symbols)

The scale of the map can be changed in stages (50 m/cm to 500 km/cm on screen). Additionally, it can be selected whether the map should be aligned in the direction of travel (forwards) or to the North (northwards).

Blaupunkt Travelpilot DX navigation
DVD Separate one-way lanes (fine geometry) are automatically displayed with this DVD.

The DVD type (with updated fine geometry) is automatically detected and the graphic displayed in a 2nd optimized set of line thicknesses.The voice output supplements the actual navigation.

"Destination-oriented navigation in non-digitized map area" function
On journeys outside the digitized map area (e.g. company premises, etc.), but still within the DVD map boundary, the navigation processor switches over to "Destination-oriented navigation in non-digitized map area".

The LCD display of the COMAND operating, display and control unit displays the message:
^ "OFF ROAD"

Additionally, if the vehicle is outside the DVD map boundaries (outside the country), the following message appears:
^ "OFF MAP"

Upon entering the OFF-ROAD mode, the road map is displayed and route information shown.

In both cases only basic position finding (dead reckoning) with correction by GPS data takes place
Limited destination guidance takes place while only specifying:
^ Distance to the destination as the crow flies
^ direction to destination (as arrow).

After reentering the digitized map area, the system automatically continues with "Destination guidance in digitized map area". The GPS position is used to help determine the roads on which the vehicle could be located. During this process a slight delay in the route guidance may result.

In the event of the message "OFF MAP", comprehensive destination-oriented navigation can be continued after loading a corresponding abroad DVD.