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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
4. V2 - BASIC CONCEPT 
The idea behind the second version is measuring height in a 
single image by profile detection. If a straight line is projected 
on a smooth surface and an image is taken from oblique camera 
position, the line appears straight on the image (Figure 4). 
Based on similar triangles clear correspondence can be defined 
between y and x, which is a quadratic equation. For x the 
function is the following: 
x = f(h,t,c,y) 
(1) 
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Figure 4. The concept of the second version 
In case of height change (an object or pothole, for example), the 
image of the line seems straight only from top view, but it’s 
broken from any oblique view point (Figure 5). 
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laser 
h-x 
Figure 5. The basic concept of measuring height (x) in a single 
image taken from oblique viewpoint. 
During the calibration, the camera focal length is considered as 
constant. So the only inputs of calibration are the h and t values. 
This system can be considered much robust compared to the 
previous version, since it avoids stereo imagery. Moreover, in 
this concept every single points of the projected line can be 
evaluated and measured (note, that previously separated points 
have been projected); therefore it enables much higher 
resolution for the road surface model. The surface resolution 
depends on the camera cross-directional resolution. Initially 
only a single line is projected onto the surface, later, if higher 
measurement speed is needed, more lines can be projected 
simultaneously. 
5. FIRST TESTS WITH V2: CONCEPT PROOF 
In the first phase the image processing module has been 
developed. For the concept proof an industrial laser line 
projector and an industrial digital camera were used, the same 
equipments are intended to apply in the final version. The laser 
projector is a 5 mW, 660 nm Lasiris laser diode, with special 
optic for the structured light. The imaging unit is a 
ThelmagingSource DFK 41F02 color camera with 1280 x 960 
resolution and 7.5 fps image acquisition speed. 
The laser projector was mounted vertically (perpendicularly to 
the surface); the projected line was captured by the camera from 
the oblique position of about 45 degrees. 
In all cases the objects have been moved towards the camera, 
perpendicularly to the projected line. Sequences of camera 
images were the inputs of the overall object reconstruction 
procedure. In all images the red laser stripe was extracted by 
filtering and binary image morphology, and then the у image 
coordinates of the laserline were computed. 
The accuracy of the reconstructed object depends on the 
capturing resolution (number of images per object) and the 
calibration parameters (camera height, object distance). In the 
following the computed cross sections and the reconstructed 
object are shown (Figure 6). 
As it can be seen in Figure 6, the detected object is nicely 
reconstructed. The accuracy of the height measurement ensures 
adequate solution for road condition detection, since the final 
purpose is measuring the height differences on the road surface 
and deriving the IRI number (roughness index) for dedicated 
road segments. 
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