Individual traffic guidance systems 
This class of systems is made for single users in their own car 
using individual information for a single trip. This information or 
hints can be used by the driver or not. The competence for 
decision is dedicated individually to the traffic participant. These 
type of car navigation systems is also called „Autonomous 
Navigation System“. This means the whole navigation 
information and the digital road map are installed inside the car 
and the onboard computer provides the optimal routing to the 
destination. This type of car navigation system provides 
continuously driving recommendations (turn by turn) to the 
driver. Some of these systems provide this information by audio 
systems due to safety reasons. There are different philosophies in 
Europe and Japan regarding the driver’s safety operation mode of 
car navigation systems. 
Most important benefit of autonomous systems is the individual 
operation without any support from the infrastructure. 
Disadvantage is the missing up-to-date traffic incident 
information and service information from the outside world. 
Therefore electronic and car navigation industry is heading to 
infrastructure supported traffic guidance systems in which case 
the onboard computer communicates continuously or time by 
time via mobile communication with a data base center of the 
roadside infrastructure. Most important bottle necks for the 
introduction of reliable up-to-date traffic information is the 
availability of traffic incident information. High priority has to be 
given to reliable operation of car navigation systems. Most 
important function is road accurate positioning, availability of 
appropriate digital road maps, and development of information 
strategies for the extraction of precise driver information at the 
next turn. 
3 POSITIONING SENSORS 
Wheel sensors (odometer) for anti-blocking systems (ABS): 
We have to decide between measurement principles: 
1. Inductive sensors for turn frequency measurement are cheap 
and are used very often. Theses sensors are not suitable for 
low. velocities (1 m/sec.). 
2. Hall sensors are very important, and need their own power 
source but can be used independently of the frequency of the 
wheels. This means, they can be used for low velocity levels 
(Westbrook 1994), (Zhao 1997). 
Magnetic field sensor/Electronic compass 
Magnetic field sensors measure the vector of all magnetic forces 
so that the magnetic field vector of the vehicle itself has to be 
reduced by calibration. Due to magnetic disturbances inside the 
vehicle, for example change of position of moving roof screen 
heating, etc., influences the calibration parameter of the system. 
The effort to reduce these effects is so high that magnetic field 
sensors mutually will not be used in the future inside of car 
navigation systems. 
Gyros 
Piezoelectric vibration gyros are robust due to missing rotating 
masses and are ideal for onboard operation in vehicles. Main 
problems of very cheap sensors are the systematic sensor errors as 
scale and bias and temperature-dependent drifts. Experiences 
have shown that constant parts of scale and bias can be estimated 
with high accuracy during curvature matching processes. 
GPS 
The largest error budget of navigation with GPS results from 
selected availability of GPS-systems. There the positioning is 
only possible in a level of accuracy of approx. 100 m. 
Main disadvantage of GPS-supported navigation systems in urban 
areas are masking effects and the selected availability of 65-85% 
due to this effect. Therefore hybrid approaches have to be used as 
map matching technologies as described in this paper. 
Integrity 
I I I I ^ Accuracy 
1 10 100 1000 [m] 
Picture 3: Availability of GPS 
DGPS 
DGPS-systems are very well known in geodesy. With the 
introduction of DGPS-services as SAPOS in Germany and the 
radio data system RDS, a continuos nationwide network of DGPS 
correction data is available since 1999. First results show an 
accuracy of approx. 5m - obviously sufficient for a lot of car 
navigation problems also in urban areas. Nevertheless the 
availability of SAPOS-DGPS-data in urban areas has to be 
emerged. 
Hybrid Systems 
This board autonomous navigation system, the principle of dead 
reckoning by means of magnetic field sensors, gyros, odometers, 
and differential odometers, relative positioning towards the 
starting point of a track are measured. Contrary to navigation 
applications in sea and air applications, vehicles have to move on 
a selected network of roads or rail tracks. Measured tracks of 
autonomous navigation systems can be compared with possible