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.