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Figure 4. Video processing in VideoCar 
2.4 Object georeferencing 
Input data for data processing are field measurements: 
e Video images 
e  Trajectory 
e Camera calibration data 
The first step in data processing is time synchronisation of 
video images to reference time of the GPS system. Both data 
are captured independent. GPS measurements are captured in 1 
second period while the video time unit lasts 1/25 of a second. 
The geometry of vehicle's trajectory can be derived from image 
measurements of distinctive points. Then it is compared to the 
GPS trajectory and mark the time point where the curves are 
identical. Time synchronisation of video images with GPS time 
introduces adjustment of a complex mathematical model which 
combines GPS measurements with photogrammetric 
measurements. Results of this procedure are georeferenced 
video images. 
Image measurements are also carried out for all objects that we 
would like to georeference. Results of image measurements are 
image co-ordinates. Combining the image measurements with 
georeferenced video images we get input data for last step in 
object georeferencing. 
In the case of stereo image measurements, space co-ordinates of 
objects are computed from known algorithm for 
stereophotogrammetric resection. The required input data for 
this algorithm are relative orientation of video cameras and 
their position in co-ordinate system of reference (state co- 
ordinate system). Space co-ordinates of objets can be also 
determined in a single image restitution. In this case, image co- 
ordinates of the selected object are measured in several 
consecutive video frames. From the object in the reference co- 
ordinate system through the camera focus is constructed a space 
line for each event of the image measurement. Bundle of space 
221 
lines intersects on the selected object. Intersection of these lines 
determines space co-ordinates of the object. 
  
gg eset 
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3 
  
  
  
  
  
Figure 5. Stereo and multi-single image restitution 
2.5 Road width measurements 
  
  
  
  
  
Figure 6. Road width measurement concept 
The road width is determined with intersection of plane 
constructed through camera focus and plane on the road level. 
For accurate measurements of the road width the lens distrosion 
acquired in camera calibration procedure has to be known. The 
main problem in measuring road width in this procedure is 
unambiguously defining the roadside. It often appears that road 
does not have any side marks or they are indefinable. 
3. PRCTICAL EXPERIENCES WITH SYSTEM 
Experiences with the system will be shortly briefed from 
project carried out in co-operation with Directorate of the 
Republic of Slovenia for Roads. Mobile mapping system 
VideoCar was used in extensive countrywide project in 
Slovenia. The aim of the project was to obtain the geolocation 
and geometry of the tourist signalisation on the state roads. 
3.1 Route planning 
Daily routes had to be carefully planned in optimal loops 
around the GPS reference points. Reference points were 
selected on chosen locations to achieve baselines shorter than 
50 km. For the project, there were 43 planned routes. The 
average length of the route was about 134 km, ranging 
particular routes from 94 km to 163km. The length of the route