GF82.61-P-2010TM Position Finding and Destination-Oriented Navigation, Function
GF82.61-P-2010TM Position Finding And Destination-oriented Navigation, Function
- with CODE (527) COMAND APS with single DVD drive (with navigation)
- with CODE (530) COMAND APS USA (with navigation system)
Determination of location is the calculation of the vehicle's current position. It is activated by opening the driver door or by switching on the ignition and is run by the navigation processor (N41/1). During the switch-on phase (software is loaded), only the basic position finding is available. Once the ignition is switched off all important position finding parameters are stored during a run-on time of 30 minutes.
3 complementary methods are utilized for continuous position finding. This ensures very accurate and reliable position finding.
These methods are:
^ Basic position finding
^ Map-based position finding
^ Global Positioning System (GPS) position finding
Manual entry of vehicle location
For a manual input of the vehicle location, it is possible to manually enter the location. This may be useful after the vehicle has been transported (e.g. ferry or train) if there was no GPS reception at the start of the journey.
Basic location finding
Basic position finding is the basic function of continuous position finding. It is carried out continuously by the navigation processor with "Circuit 15R ON" and is independent from the digital versatile disk (DVD) ROM map. After "Circuit 15R OFF" the current position is stored. The following information is calculated with the aid of basic position finding:
^ Travel distance covered
^ Direction of travel (backwards or forwards)
^ Vehicle alignment
The basic position finding is performed approx. every 1 s.
Distance traveled
The wheel rotation direction signal is determined by the left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3) right rear rpm sensor (L6/4) and is read in discretely by the ESP control unit (N47-5). This message is sent on the Controller Area Network Bus class C (engine compartment) (CAN-C) and transmitted by the central gateway control unit (N93) to the Controller Area Network bus class B (interior) (CAN-B). As a result, the navigation processor detects the direction of travel (forward or reverse).
Direction of travel
The navigation processor receives the wheel speed signals from the ESP control unit as described above. Evaluation of the wheel speed signals results in the travel distance covered.
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.
Errors with basic position finding
Rolling when the ignition is switched off or transport of the vehicle also distort the position finding. In both cases, this deviation is automatically corrected by the navigation processor on receipt of the GPS data.
Calibration
Wheel calibration is necessary following a tire change. To this end, it is necessary to enter the tire size, e.g. 225/60/16 and the coding as to whether new (depth of tread approx. 5 to 10 mm) or used tires (depth of tread approx. 3 to 5 mm) have been mounted. Entries are made using STAR DIAGNOSIS or directly on the COMAND operating, display and controller unit (A40/3). A special calibration journey is not required.
Recalibration
The difference between the calculated mileage and actual mileage covered between 2 turning-off points is used to re-calibrate the tire circumference automatically.
GPS position finding
The GPS is a satellite-assisted positioning system that has been set up by the United States Department of Defense. It is free and available worldwide. The GPS satellites permanently transmit time and position data.
4 satellites are needed for the first position calculation, then 3 receivable satellites are sufficient. The GPS position finding is, in particular, for journeys outside the digitized map area and after transportation of the vehicle (e.g. train, ferry and towing) irreplaceable. Starting GPS position finding again (following interruption of the satellite reception) may take several minutes (for initial startup of the device up to 20 min).
The navigation processor calculates the location of the vehicle and the accuracy of positioning from the satellite signals received and amplified by the GPS antenna (A2/49a2).
The actual calculation is essentially based on the measurement of the runtimes of the signals transmitted synchronously by the various satellites. An important requirement here is the synchronicity of the clocks for the satellites and the receiver. To this end the receiver is equipped with an automatic time correction, which in turn is made possible with the aid of the satellite signals. If the navigation processor determines that the basic location finding is less accurate than the GPS location finding, the currently calculated position is corrected using the GPS data. Moreover, the route of the vehicle is determined from the sequence of locations calculated with GPS.
Every minute, approximately 50 GPS recalculations of the location take place.
Possible interference when receiving GPS signals
Since GPS operates in the gigahertz (GHz) range (microwaves) and the signals are weak, reception interference can occur as the result of:
^ Atmospheric interference, e.g. weather, water vapor, fog
^ Multi-path reception due to signal reflections, e.g. frombuilding walls
^ Interruption of signal reception, e.g. in areas with superstructures and in the vicinity of tunnels, tall buildings, trees
GPS reception therefore necessitates a clear view of the sky. Positioning accuracy lies at approx. 10 m.
Map-based position finding
Map-based position finding is only available in the digitized area of the DVD ROM map. By comparing the calculated position of the vehicle with the DVD-ROM map, the deviation can be detected and automatically corrected.
Function
The position of the vehicle is continuously followed on the DVD ROM map by the navigation processor. In the event of deviations from the calculated routes in the course of the trip, the position coordinates of the basic position finding will be corrected if necessary.
Destination-oriented navigation
Destination-oriented navigation includes making up and outputting driving recommendations to guide the driver to the desired destination. Destination-oriented navigation is contingent on:
^ Continuous position finding is in operation.
^ The trip destination has been entered.
^ Route calculation done.
The navigation processor continuously compares the route calculation data with the location finding data and derives from this measures for further destination-oriented navigation.
Depending on the position of the vehicle, a differentiation is made between the following 2 modes of destination-oriented navigation:
^ Destination-oriented navigation within the digitized DVD-ROM map area
^ Limited destination-oriented navigation outside the digitized DVD ROM map area
For trips within the digitized map area, the following information is available to the user:
^ Current position and route of vehicle on digitized map (graphically displayed)
^ List of routes
^ Distance from the destination and likely time up to arrival
^ Travel direction recommendation
^ Travel direction arrow
^ Name of current road
^ Name of the next road into which the vehicle should turn
^ Distance to next turning-off point (stated in length units or as a bar graph)
The compass direction of north, south, east or west is given by a graphic display and voice output. The compass direction is displayed only in the case of numbered roads. No data and display of the compass direction is given in the case of roads designated by name (e.g. within towns).
There are 3 types of display available for the destination-oriented navigation:
^ Map
^ Map and symbol presentation of the turn-off points
^ Symbol presentation (system of navigation symbols)
The scale of the map can be changed in stages. In addition to this a selection can be made as to whether the map is to be aligned in the direction of travel (Head-Up) or towards the North (North-Up).
The DVD type (with the latest fine geometry) is automatically detected and the graphic is displayed in an optimized 2nd set of line thicknesses.
The actual destination-oriented navigation is mainly supported by the voice output.
When traveling outside the digitized map area (e.g. company grounds, multi-level car parks, dirt roads, etc.), but still within the DVD-ROM map boundaries, the navigation processor switches over to "Destination-oriented navigation in non-digitized map area". The message "OFF ROAD" appears in the display of the COMAND operating, display and controller unit. If the vehicle is outside the DVD-ROM map boundaries (outside the country), the message "OFF MAP" appears..
In both cases, only the basic position finding continues to operate with correction using the GPS data. Restricted destination-oriented navigation is accomplished by indicating only the following information:
^ Straight-line distance to the destination
^ Direction to destination (as an arrow)
After reentering the digitized map area, the system automatically continues with "Destination-oriented navigation in digitized map area".
The GPS position can be used to determine the possible roads, on which the vehicle may be located. During this process a slight delay in the destination-oriented navigation may result.
When the message "OFF MAP" appears, complete destination-oriented navigation can be continued by inserting the proper DVD-ROM for the foreign country.
The time synchronization between the COMAND operating, display and controller unit and the instrument cluster (A1) must be performed on journeys in different "time zones" (time shift, time change).
Dynamic route guidance with code (527) COMAND APS with single DVD drive (with navigation)
The current traffic situation is taken into consideration in the dynamic route guidance. The incoming information on the traffic situation can be received by the radio data system/traffic message channel (RDS/TMC) function with the FM receiver in the audio gateway control unit. The information on the current traffic situation is sent out by a specially equipped broadcasting corporation on an area-related basis via FM. A suitable FM/RDS transmitter must be tuned in. The FM receiver receives the traffic reports from the left antenna amplifier module (A2/64) and passes them on to the traffic data recorder.
The traffic reports are stored in the traffic data recorder of the COMAND operating, display and controller unit and made available to the navigation processor.
The services of the Traffic Message Channel (TMC) are coded, i.e. a decoder is necessary for this reception (fee required, but better service), or uncoded (free of charge).
Since no communication is accomplished between the vehicle and broadcasting corporation with TMC messages, the traffic data recorder selects the traffic messages related to the route on which the vehicle is presently driving as well as the surrounding area.
Evaluation of traffic information with code (527) COMAND APS with single DVD drive (with navigation)
The traffic data recorder decodes the traffic information and forwards it internally to the navigation processor upon request. The navigation processor makes the decision whether the route should be changed. If necessary, a message that the route should be changed is output via the vehicle speaker. For synchronization tasks, the traffic data recorder requires an up-to-date "location list" from the navigation processor. In this list every stretch and every significant point (e.g. highway exit) on the recorded road network is identified by a unique number. This list is originally stored on the DVD-ROM. It is automatically loaded into the traffic data recorder as required (e.g. when DVD-ROM is changed). The traffic information stored in the traffic data memory is erased automatically after half an hour, max. 100 messages can be stored.
The decoded traffic messages are highlighted on the map by means of corresponding symbols. They can also be displayed as plain text. To do this, press the "TRAFFIC JAM" button
Traffic reports relevant to the route are, for example:
^ Road blocked
^ Jam
^ Slow-moving traffic
^ Heavy traffic
^ Light traffic
^ Road works
^ Trouble-free traffic
In the "Navigation" menu, the list of traffic information can be called up by pressing the "TMC message displays" button.
