GF82.61-P-2010TMA Position Finding and Destination-Oriented Navigation, Function
GF82.61-P-2010TMA Position Finding And Destination-oriented Navigation, Function
- with CODE (525) MB Audio 50 APS radio
Determination of location is the calculation of the vehicle's current position. It is activated as soon as the driver door is opened or by switching on the ignition and is performed by the integrated navigation processor of the radio control panel and navigation unit (A2/56). 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.
Position finding uses 3 methods, which mutually complement each other and therefore ensure 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
It is possible to enter the location manually via the radio control panel and navigation unit. In the following instances this can be useful:
^ following transport of the vehicle (e.g. by ferry or train)
^ If at the start of a journey GPS reception was not possible
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 ESP control unit (N47-5) reads in the rpm signals of the following sensors and places these rpm signals on the Controller Area Network Bus class C (engine compartment) (CAN-C):
^ Left front rpm sensor (L6/1)
^ Right front rpm sensor (L6/2)
^ Left rear rpm sensor (L6/3)
^ Right rear rpm sensor (L6/4)
The central gateway control unit (N93) receives these rpm signals and transmits them to the Controller Area Network bus class B (interior) (CAN-B). The audio gateway control unit (N93/1) transmits them to the Media Oriented System Transport (MOST). As a result, the radio control panel and navigation unit, which is also a MOST participant, can calculate the distance traveled.
Direction of travel
The integrated navigation processor can detect the direction of travel (forward or reverse) through the signal for the wheel rotation direction, which is transmitted by the audio gateway control unit via the MOST to the radio control panel and navigation unit.
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. 225/060/016 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 fitted. The values are input via STAR DIAGNOSIS or directly at the radio control panel and navigation unit. A special calibration journey is not required.
Recalibration
Because of the tire abrasion, a constant recalibration of the tire circumference is required. It is carried out automatically and uses the difference between the calculated and actually traveled distance between 2 turning points calculated with the aid of map-based position finding.
GPS position finding
The GPS is a satellite-assisted localizing system that has been set up by the American Ministry of Defense. It is free and available worldwide.
Various GPS satellites constantly 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. A new GPS position (after interruption of the satellite reception) can take several minutes (up to 20 minutes when the equipment is commissioned).
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 prerequisite for this is the synchronicity of the clocks, 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
As GPS operates in the giga hertz (GHz) range (microwaves) and the signals are weak, reception interference can occur as the result of the following events:
^ Atmospheric interference, e.g. inclement weather, water vapor, fog
^ Multi-path reception due to signal reflections, e.g. from building walls
^ Signal shadowing, e.g. in built-up areas and in tunnels, by high buildings, by 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 CD-ROM map. By comparing the calculated position of the vehicle with the CD-ROM map, the deviation can be detected and automatically corrected.
Function
The navigation processor constantly tracks the vehicle's position on the CD-ROM map.
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.
Route calculation
After input of the destination via the radio control panel and navigation unit, the route is calculated and continuously updated by the navigation processor. It can only be calculated within the digitized map area. The calculated route is a precondition for destination-oriented navigation.
The navigation processor calculates the route with the aid of the map data, the destination entered, and the current position. For the calculation it takes into account roads and their attributes read from the 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:
^ Quickest route
^ Shortest route
^ Dynamic route
Furthermore, certain route sections can be avoided when making the selection.
Under "Own selection", the following stretches can be excluded from the route calculation:
^ Highway
^ Ferry
^ Toll road
^ Tunnel
^ Car loading
After calculating the route, the navigation processor creates a list of roads to travel on and turns to take as well as the time it takes to reach the destination. This list of routes is drawn on for destination-oriented navigation. It may also be displayed by calling up the "Route information" menu.
Trips outside the digitized map area
If the vehicle leaves the digitized map area (e.g. driving in a multilevel car park), then no route can be calculated or updated. "OFF ROAD" appears on the display of the radio control panel and navigation unit. Upon leaving the map area (e.g. foreign country), the message "OFF MAP" appears. Destinations that lie outside the digitized map area cannot be incorporated into the route calculation.
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 CD-ROM map area
^ Restricted destination-oriented navigation outside the digitized CD-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. It is also possible to choose whether the map should be aligned in the direction of travel or Northwards.
The CD type (with the latest fine geometry) is automatically detected and the graphic is displayed in an optimized second 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) but still within the CD-ROM map boundaries, the navigation processor switches over to "Destination-oriented navigation in non-digitized map area". The message "OFF ROAD" appears on the display of the radio control panel and navigation unit. The message "OFF MAP" is displayed if the vehicle is outside of the CD-ROM map boundaries (outside the country).
In both cases, only the basic position finding continues to operate with correction using the GPS data. Limited destination-oriented navigation is accomplished by indicating only the 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 CD-ROM for the foreign country.
The time synchronization between the radio control panel and navigation unit and the instrument cluster (A1) must be performed on journeys in different "time zones" (time shift, time change).
Dynamic route guidance
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 radio control panel and navigation 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 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.
Traffic information analysis
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 CD-ROM.
It is automatically loaded into the traffic data memory as required (e.g. when CD-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.
