The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
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3. RESEARCH APPROACH 
3.1.4 Ortho-image and Contour 
An overview of the research procedure developed for pavement 
distress evaluation is presented. A combination of close-range 
photogramme trie and image processing metrology were 
developed in various stages and is illustrated in Figure 1 and 6, 
respectively. 
After performing the steps in VirtuoZo digital photogrammetry 
workstation, ortho-image and contour overlay as well as 3D 
DEM data was generated. Figures 3 and 4 show the ortho 
image and contour overlay of pothole (disintegration) distress 
respectively. 
3.1 Photogrammetric System 
In the first stage, a stereovision measurement technique is 
developed to evaluate and monitor the pavement conditions. To 
achieve this, several processes were conducted. These processes 
were categorized as, camera calibration, ground control, image 
acquisition and digital photogrammetry workstation (VirtuoZo) 
processing. The following sections describe these processes. 
3.1.1 Ground Control 
Ground control is currently provided by means of a frame that 
was calibrated in the laboratory. This arrangement was chosen 
because it is convenient to be used in the field. 
Figure 3. Relative orientation of stereo image 
Figure 1. Schematic diagram of the photogrammetric system 
3.1.2 Image Acquisition 
1' 
Ten pairs of stereo images were captured using the same digital 
i camera with its axis perpendicular to the road surface. Stereo 
% vision technique showed great potential for metrology 
application in pavement condition monitoring. 
3.1.3 PW (VirtuoZo) Processing 
DPW processing was carried out using the VirtuoZo NT system 
(version 3.2) running on a workstation. The process has two key 
steps (1) Requirement and parameter setup for VirtuoZo and (2) 
Running VirtuoZo software. VirtuoZo, which is low user 
interaction software, had proved highly flexible and is easy to 
use in terms of preparation modules (for example, creating 
image overviews and automatic image orientation) for ortho 
image and digital elevation model generation. 
Figure 4. Ortho-image and contour overlap of pothole 
3.1.6 Severity Classification 
3D DEM coordinates output from VirtuoZo became the input 
data for SURFER software and MATLAB to produce contour 
plotting and cross section plotting respectively. SURFER 
consisted of three programs: QGRID, TOPO and SURF. 
QGRID takes irregular data from ASCII file and created a 
regularly spaced ‘grid’. The reformatted file was then entered 
into a graphics programs, TOPO or SURF. TOPO created 
topographic maps and SURF created three dimensional terrain 
surfaces. The 3D surface as shown in Figure 5 shows that the 
Y-axis coordinates were positive in the direction of traffic 
movement; the X-axis coordinates represented the 
measurements crossing the road; and the Z-axis coordinates 
area were positively upward.