GF82.61-P-2010SX Position Finding and Destination-Oriented Navigation, Function
GF82.61-P-2010SX Position Finding And Destination-oriented Navigation, Function
- with CODE (527) COMAND APS with single DVD drive (with navigation)
"Continuous position finding" function
Continuous location finding means that the current position of the vehicle is calculated. It is active when transmitter key (A8/1) is in position 1 (circuit 15R ON) and is performed by the navigation processor integrated in the COMAND controller unit (A40/3). 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 localizing parameters are stored for the duration of the run-on time (30 min). Once the run-on time has ended, the COMAND controller unit switches off completely.
After the last execution in the destination-oriented navigation (destination reached), the position map is shown again on the COMAND display (A40/8).
Continuous position finding uses 3 methods, which mutually complement each other and therefore ensure very accurate and reliable position finding: These are:
^ Basic position finding (dead reckoning)
^ Global Positioning System (GPS) position finding
^ Map-based position finding
Manual entry of vehicle location
There is the option to manually enter the location via the front central operating unit (A40/9) in the "Navigation" menu of the integrated navigation processor of the COMAND controller 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
Component Identification:
"Basic position finding" function
Basic position finding is the basic function of continuous position finding. It is constantly carried out by the integrated navigation processor of the COMAND controller unit as of transmitter key position 0 (circuit 15C ON). The function is shown on the COMAND display in the event of transmitter key position 1 (circuit 15R ON), together with the COMAND controller unit being active and the current vehicle position being requested via the front central operating unit. Basic position finding (dead reckoning) takes place independently from the digitized map.
When the transmitter key is turned back into position 0 (circuit 15C ON), the COMAND controller unit is switched off. However, the current position of the vehicle remains 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) (installed at the traction system hydraulic unit (A7/3)) reads in the signals of the following sensors and forwards them via the chassis CAN to the central gateway control unit (N93):
^ 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 forwards the rpm signals received via the central CAN to the navigation processor integrated into the COMAND controller unit for evaluation, which then uses them to calculate the distance traveled.
Direction of travel
The integrated navigation processor recognizes the direction of travel (forward or reverse) through the signal for the direction of rotation of the wheel, which is transmitted by the central gateway control unit via the central CAN to the COMAND controller unit.
Vehicle orientation
The navigation processor integrated into the COMAND controller unit uses the data of the turn rate sensor (gyrosensor) and the sequence of locations calculated with the GPS to calculate the orientation (compass direction) of the vehicle.
Errors with 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 of the COMAND controller unit as it receives 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. The data are entered via STAR DIAGNOSIS or directly via the front central operating 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.
Component Identification:
"Position finding via GPS" function
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 an 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).
Every minute, roughly 50 GPS new calculations of the location are performed.
The integrated navigation processor of the COMAND controller unit calculates the vehicle location and the accuracy of the position finding based on the satellite signals received and amplified by the telephone and GPS roof antenna (A2/49) (model 221) or by the telephone and GPS antenna (A2/49) (model 216).
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. For this purpose, the receiver has an automatic time correction feature, which is made possible with the aid of the satellite signals. If the navigation processor of the COMAND controller unit 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 to this the sequence of locations calculated by the GPS is used to determine the vehicle's route.
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. 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 high buildings, through trees
GPS reception requires a clear view of the sky. Positioning accuracy lies at approx. 10 m.
Component Identification:
"Map-based position finding", function
The position of the vehicle is constantly tracked on the map by the integrated navigation processor of the COMAND controller unit. In the event of deviations in the course traveled from the calculated route, the position coordinates of the basic location finding are corrected.
Map-based position finding is only available in the digitized area of the map. By comparison with the calculated position of the vehicle with the map, the deviation can be recognized and corrected automatically.
"Route calculation" function
After entering the destination at the front central operating unit, the route is calculated by the navigation processor integrated into the COMAND controller unit and constantly updated. 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
^ Separate selection
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
Toll roads are color coded on the map.
After calculating the route, the navigation processor integrated into the COMAND controller unit 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.
Dynamic route calculation with code (527) COMAND APS with single DVD drive (with navigation)
When the user selects "dynamic route" option, traffic messages received via two-way radio (ultra-short waves (FM [UKW]) or network provider) are stored with the aid of a traffic data recorder integrated in the navigation processor and automatically taken into consideration when the route is calculated. The route is then calculated with the optimum time, in a manner similar to the "Fastest route" option. Notification that the route has been recalculated taking traffic messages into consideration, is provided.
Route updating
If the driver deviates from the calculated route, the navigation processor integrated into the COMAND controller unit calculates a new route list. When doing so, the current position and the direction of travel are taken into consideration. The message "New Route" appears on the COMAND display and "NEW RTE" appears in the multifunction display (A1p13).
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 in the COMAND display. 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.
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 and the distance to the start of the traffic jam
^ The corresponding stretch should be blocked within the detailed list of routes.
"Destination-oriented navigation" function
Destination-oriented navigation is the compilation and output of route recommendations to guide the driver to the desired destination. Destination-oriented navigation is contingent on:
^ Continuous position finding in operation (executed automatically).
^ Destination was entered
^ Route calculation done.
The navigation processor of the COMAND controller unit continuously compares the route calculation data with the data of the continuous position finding. This is used to derive further measures for the destination-oriented navigation. Depending on the position of the vehicle, a distinction can be made between 2 destination-oriented navigation modes:
^ Destination-oriented navigation within the digitized 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 processor of the COMAND controller unit is made available:
^ The current position and route of the vehicle on a digital map
^ List of routes
^ Distance to destination and estimated trip duration up to arrival
^ Travel direction recommendation
^ Travel direction arrow
^ Name of current road
^ Name of the road 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 (sign symbols)
The scale of the map can be changed in stages. Moreover, the orientation of the map (in direction of travel or facing North) as well as the type of representation (e.g. 2-dimensional, 3-dimensional, with geologic coordinates) can be selected
"Destination-oriented navigation in the non-digitized map area" function
When traveling outside the digitized map area (e.g. company grounds etc.), but still within the map limits, the navigation processor of the COMAND controller unit switches over to "Destination-oriented navigation in non-digitized map area". The message "OFF ROAD" appears on the COMAND display. If in addition, the vehicle is outside the map limits (outside the country), the message "OFF MAP" appears:
When entering the OFF-ROAD mode, the street map and a route information is shown on the COMAND display.
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:
^ 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 is used to help determine the roads on which the vehicle could be located. During this process a slight delay in the destination-oriented navigation may result.
In the event of the message "OFF MAP", comprehensive destination-oriented navigation can be continued after loading a corresponding DVD for the foreign country.
