GF82.61-P-2010FAB Position Finding and Destination-Oriented Navigation, Function
GF82.61-P-2010FAB Position Finding And Destination-Oriented Navigation, Function
MODEL 203.7
- with CODE (525) MB Audio 50 APS radio
MODEL 203.7 as of model year 09/YoM 08 model refinement package
Basic position finding
Map-supported location finding
Global Positioning System (GPS) position finding
Function requirements
- Status "Circuit 30 ON"
- The radio and navigation unit (A2/56) is operating properly
General
Position finding is understood to mean the calculation of the vehicle's position at any given time. This function is active when the ignition is switched on and is carried out by the navigation processor, which is integrated in the radio and navigation unit. During the switch-on phase (software is loaded), only the basic position finding is available. After switching the ignition off, all important positioning parameters are stored for the duration of the run-on time (approx. 30 min).
Manual entry of vehicle location
It is possible to enter the location manually on the radio and navigation unit in the "Navigation" menu.
Position finding uses the following methods, which mutually complement each other and thus ensure very accurate and reliable position finding:
- Basic position finding (dead reckoning)
- GPS position finding
- Map-based position finding
Destination-oriented navigation is the compilation and output of route recommendations to guide the driver to the desired destination. The navigation processor of the radio and navigation unit continuously compares the route calculation data with the position finding data to deduce the further navigation. The operating principle depends on whether the vehicle is within or outside of the digitized CD map area.
Following the final navigation execution (destination reached), the position map is displayed again. After a run-on time of 1 min, the radio and navigation unit switches itself off completely.
The position finding and destination-oriented navigation function is divided into the following subareas:
- General information on basic position finding
- Basic position finding function sequence
- General information on GPS position finding
- Function sequence for GPS position finding
- General map-based position finding
- Function sequence for map-based position finding
- Function sequence for route calculation
- Function sequence for navigation in the digitized map area
- Function sequence for navigation in the non-digitized map area
Basic position finding
General information on basic position finding
The navigation processor of the radio and navigation unit is continuously performing basic position finding when the ignition is switched on.The current position is stored after the ignition is switched off.
The following information is calculated with the aid of basic position finding:
- Distance traveled
- Direction of travel (forwards or backwards)
- Vehicle alignment
For this, the radio and navigation unit needs the following information:
- Wheel speed signals
- Distance traveled data
- Vehicle alignment (cardinal points)
- Data for direction of travel (forward or reverse)
The basic position finding is performed approx. every 1 s.
Basic position finding function requirements
- Communication with the ESP and BAS control unit (N47-5) is free of faults
Basic position finding function sequence
The radio and navigation unit receives the wheel speed signals from the left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3) and right rear rpm sensor (L6/4) in the following way:
- Direct line
- ESP and BAS control unit
- Engine compartment CAN
- EIS [EZS] control unit (N73)
- Interior CAN
The data of the turn rate sensor (gyro sensor) integrated in the radio and navigation unit for determining the vehicle alignment (cardinal points), is forwarded within the radio and navigation unit.
The radio and navigation unit receives the data on the direction of travel (forwards or backwards) by way of wheel speed signals in the following way:
- ESP and BAS control unit
- Engine compartment CAN
- EIS [EZS] control unit
- Interior CAN
Errors during basic position finding
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.
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. Entries are made using Star Diagnosis or directly on the radio and navigation unit. A special calibration journey is not required. The difference between calculated and actual travel distance covered between 2 turning-off points is used for automatic re- calibration of the tire circumference (made necessary because of tire wear).
Location finding with GPS
General information on GPS position finding
The GPS is a satellite-assisted positioning system that has been set up by the US Ministry of Defense. It is free and available worldwide. Different GPS satellites constantly transmit time and position data, whereby approximately 50 new GPS calculations are made of the location every minute. 4 satellites are needed for the first position calculation, then 3 receivable satellites are sufficient.
The actual calculation is based on the measurement of the transmission times 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. When the navigation processor determines that basic location finding is less precise than GPS location finding, the currently calculated position is corrected with the aid of the GPS data.
In addition to this the sequence of locations calculated by the GPS is used to determine the vehicle's route.
GPS position finding is irreplaceable for journeys outside the digitized map area and after vehicle transport (e.g. train or ferry journeys and towing). 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).
Possible problems in GPS signal reception
Since GPS operates in the giga hertz (GHz) range (microwaves) and the signals are weak, reception interference can occur as a 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 blocking, e.g. in built-over areas and in tunnels, through high-rise buildings, trees
GPS position finding function requirements
- Proper GPS reception
Function sequence for GPS position finding
The navigation processor of the radio and navigation unit calculates the position of the vehicle and the accuracy of positioning using the satellite signals received and amplified by the GPS antenna (A2/49a2).
The GPS antenna is integrated in the antenna system (A2/49) on the roof.
Map supported location finding
General map-based position finding
A map-based position finding is only available in the digitized area of the CD map. Comparing the calculated position of the vehicle against the CD map enables deviations to be detected and automatically corrected.
Function requirements for map-based position finding
- Correct navigation CD is inserted.
- Vehicle is located in the digitized area of the CD map.
Function sequence for map-based position finding
The navigation processor of the radio and navigation unit continuously tracks the position of the vehicle on the CD map. In the event of deviations in the course traveled from the calculated route, the position coordinates of the basic location finding are corrected.
Function requirements for route calculation
- Destination has been entered.
- Vehicle is located in the digitized area of the CD map.
Function sequence for route calculation
The navigation processor in the radio and navigation unit calculates the route and updates it continuously. While doing so, it takes the following data into account:
- Destination entered
- Position finding
- CD map data (streets and their attributes, such as one-way streets, bans on turns, street classes, etc.)
- Computation option (specified by the operator)
The following computation options are available:
- Quickest route
- Shortest route
- Dynamic route (traffic messages via Traffic Message Channel (TMC) are taken into account)
- Own selection (avoid freeway, ferry, toll roads or tunnel)
Following the route calculation the navigation processor compiles a list of the roads to be used and any junctions. This list of routes is drawn on for destination-oriented navigation. It may also be displayed by calling up the "Information" menu.
Route updating
When the driver deviates from the calculated route, a new route is calculated by the navigation processor. The message "New route" appears on the display and "NEW RTE" appears in the instrument cluster (A1).
Computation options for dynamic route
The TMC messages are broadcast by FM stations and transmitted via the antennas in the rear window to window antenna amplifier module 2 (A2/72) and from there to the radio and navigation unit. The integrated 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.
The traffic information stored in the traffic data recorder is automatically deleted after 30 min. A maximum of 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. For this purpose press button "Detour" and then active menu "TRAFFIC-INFO.
Digitized CD map area
1 Vehicle position within digitized CD map area
Non-digitized CD map areas:
2 Vehicle position within the CD map boundaries, but outside of the digitized map area ("OFF ROAD", company premises, dirt road)
3 Vehicle position outside the CD map limits ("OFF MAP")
Function requirements for navigation in the digitized map area
- Position finding in operation (executed automatically).
- Destination was entered
- Route calculation done.
Function sequence for navigation in the digitized map area
The navigation processor of the radio and navigation unit provides the following information to the user:
- Current position and route of the vehicle on the map
- Route list
- Distance from the destination and estimated time to arrival
- Travel direction recommendation
- Travel direction arrow
- Name of current road
- Name of the street to turn into
- Distance to next turning-off point (stated in length units or as a bar graph)
There are 3 types of display available for the destination-oriented navigation:
- With a map
- With a map and symbol display before turning-off points
- With a symbol display (guide symbols)
The scale of the map can be gradually altered (50 m/cm up to 500 km/cm). Moreover, it is possible to select whether the map is aligned in the direction of travel (forward) or facing North.
The type of CD is automatically recognized. The voice output supplements the actual destination-oriented navigation.
Function requirements for navigation in the non-digitized map area
- Position finding in operation (executed automatically).
- Destination was entered
- Route calculation done.
Function sequence for navigation in the non-digitized map area
When traveling outside the digitized map area (e.g. company premises, multi-level car parks, dirt roads, etc.), but still within the CD map boundaries, the navigation processor of the radio and navigation unit switches over to "Navigation in the non-digitized map area". The message "OFF ROAD" appears on the display of the radio and navigation unit.
If, in addition, the vehicle is outside the CD map limits (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.
Limited destination-oriented navigation is accomplished by indicating only the following information:
- Distance to the destination as the crow flies
- Direction to the destination (as an arrow)
When entering the OFF-ROAD mode, the street map is opened and a route information is displayed.
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. Here, temporary delays may occur during navigation.
In the event of the message "OFF MAP", comprehensive navigation can be continued after loading a corresponding CD for the foreign country.
