GF82.61-P-2004TXJ Position Finding and Destination-Oriented Navigation
GF82.61-P-2004TXJ Position Finding And Destination-Oriented Navigation
- with CODE (498) Japan version
"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 carried out by the navigation processor in the COMAND operating, display and controller unit (A40/3). During the switch-on phase (software is loaded), only the basic position finding is available. After switching off the ignition (circuit 15 OFF) all the vital 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 controller unit switches itself off completely.
After the last execution in the destination-oriented navigation (destination reached), the position map is shown again on the display of the COMAND operating, display and controller unit.
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)
^ GPS position finding
^ Map-based position finding
Manual entry of vehicle location
It is possible to enter the location manually on the COMAND operating, display and controller unit in the "Navigation" menu. 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 position finding" function
Basic position finding (dead reckoning) is the base function in continuous position finding. It is continuously carried out by the navigation processor in the COMAND operating, display and controller unit when the ignition is switched on and is independent of the digital versatile disk (DVD) map. The current position is stored after the ignition is switched off.
Basic position finding (dead reckoning) is used to calculate the following information:
^ Travel distance covered
^ Direction of travel (backwards or forwards)
^ Vehicle alignment
The basic position finding (composite positioning) is performed approximately every 1/s.
Distance traveled
The navigation processor in the COMAND operating, display and controller unit 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 navigation processor in the COMAND operating, display and controller unit recognizes the direction of travel (forward or reverse) through the signal for the direction of wheel rotation, which is sent by the ESP control unit and transmitted by the central gateway control unit (N93) over the Controller Area Network bus class B (interior) (CAN B).
Vehicle orientation
The navigation processor in the COMAND operating, display and controller unit uses the data of the turn rate sensor (gyro sensor) to calculate the orientation (compass direction) of the vehicle while taking the route determined with the aid of GPS into account.
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.
The deviation is automatically corrected in both cases by the navigation processor of the COMAND operating, display and controller unit when GPS data are received.
The driving direction signal (forwards or backwards) is generated by the wheel speed sensors. This enables an accurate recording of the travel distance to be made.
Recalibration
The difference in the calculated mileage and the mileage actually traveled between 2 turnoff points determined with the aid of the DVD map is used to automatically recalibrate the tire circumference (necessary due to tire abrasion).
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 COMAND operating, display and controller unit. A special calibration journey is not required.
"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 and position data. Signals from 4 satellites are required for the first position calculation. After that, signals from 3 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, approximately 50 GPS recalculations of the location take place.
The navigation processor in the COMAND operating, display and controller unit calculates the vehicle location and the position finding accuracy from 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. 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.
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. 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, tunnels, through high buildings, through trees
GPS reception requires a clear view of the sky. Positioning accuracy lies at approx. 10 m.
Function
The position of the vehicle is followed continuously on the DVD map by the navigation processor in the COMAND operating, display and controller unit. In the event of any deviation to the route from the calculated path the positioning coordinates for basic position 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.
"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 operating, display and 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 in the digitized DVD map area
^ Destination-oriented navigation in non-digitized DVD map area
"Destination-oriented navigation in the digitized DVD map area", function
During trips within the digitized map area, the following information calculated by the navigation processor of the COMAND operating, display and controller unit is available to the user:
^ The current position and route of the vehicle on a digital map
^ 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 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 (50 m/cm to 500 km/cm on the screen). Moreover, it is possible to select whether the map is aligned in the direction of travel (forward) or facing North.
Blaupunkt Travelpilot DX navigation DVD
Separate one-way lanes (fine geometry) are automatically displayed with this DVD.
The DVD type (with the latest fine geometry) is automatically detected and the graphic is displayed in an optimized second set of line thicknesses. The voice output supplements the actual destination-oriented navigation.
"Destination-oriented navigation in non digitized DVD map area", function
When traveling outside the digitized map area (e.g. company grounds, etc.), but still within the DVD map limits, the navigation processor in the COMAND operating, display and controller unit switches over to "Destination-oriented navigation in non-digitized DVD map area". The message "OFF ROAD" appears in the display of the COMAND operating, display and controller unit. If in addition, the vehicle is outside the DVD map limits (outside the country), the message "OFF MAP" appears:
When entering the OFF-ROAD mode, the street map is opened and a route information is displayed.
In both cases, only basic position finding (dead reckoning) with correction by GPS data takes place. 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 DVD 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.
In the event of the message "OFF MAP", comprehensive destination-oriented navigation can be continued after loading a corresponding abroad DVD.
"Traffic information radio channel", function
Information signs from regional traffic stations (with specified transmission frequency), which are installed on the relevant roads and freeways, are used to inform road users of transmission frequencies of radio stations giving information on the current traffic situation.
The COMAND operating, display and controller unit enables the driver to press the "Traffic Information (TI)" button in different regions to listen to the regional traffic information.
Traffic information is only broadcast regionally and not nationally. This makes it difficult to compile a comprehensive and up-to-date list with traffic jam information. Dynamic route guidance is therefore not always possible.
The information stored in the traffic data recorder is automatically deleted after t = 0.5 h. A maximum of 100 messages can be stored.
The decision as to whether the route should be altered, is made by the navigation processor of the COMAND operating, display and controller unit. It is primarily dependent on the selected route entry. The traffic data recorder requires an up-to-date "location list" from the navigation processor in order to correct the route. In this list every stretch and every significant point (e.g. highway exit) on the recorded road network is identified by a unique number. The "location list" is originally stored on the navigation DVD.
The decoded traffic messages are highlighted on the map by means of corresponding symbols. They can also be displayed as plain text. Traffic reports relevant to the route are, for example:
^ Road blocked
^ Jam
^ Slow-moving traffic
^ Road works
