International Archives of the Photogrammetry, Remote S
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Figure 3. Optimal vertical alignment on 3D image of the terrain
Increasing the number of intersection points may also decrease
the driver safety and comfort due to frequent changes on the
roadway grade. However, using more intersection points would
reduce the earthwork volume that leads to significant reduction
in earthwork allocation cost and total construction cost since the
road profile becomes closer to the ground profile.
Profile and plan view of the road alignment was shown in
Figure 4 and Figure 5, respectively. The model required two
horizontal curves and one crest vertical curve along the
roadway. The radiuses of the horizontal curves (e.g. 62.9m and
50.9m) and the length of the vertical curve (66.23m) were
acceptable for safe traffic passage. The length of road section
was approximately 396 m with gradient of 2 to 12% (Figure 4).
4. CONCLUSIONS
Using high performance microcomputers, improved software
languages, advanced remote sensing technologies, modern
optimization techniques, and high-resolution DEM data has
significantly improved the designer efficiency in designing
preliminary forest roads in the office. In this study, a 3D forest
345 [— —————————— ono
|
340 Ground |
Profile |
335 |
1 i
; |
330 12% 1 1 i
Vertical Curve
Length: 66.23 m
Elevation (m)
325
320
ee cup nier
315 :
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400
Road Length (m)
Figure 4. Profile view of the forest road
ensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
road alignment optimization model was developed as a decision
support system. Using this model, a designer can quickly
evaluate alternative paths and locate the best path with
minimum total road cost. In the model, an initial horizontal
alignment is located interactively on the 3D image of the terrain
generated based on a high-resolution DEM from LIDAR.
During the last couple of decades, LIDAR has been used in
variety of applications. Most recently, it has been used to
generate high-resolution DEMs of the forested areas with
sufficient accuracy. The model also relies on available GIS
layers of attribute data to represent topographic conditions.
Available GIS data collected from the forested areas currently
cannot represent the actual topographic condition with a high
accuracy; however, quality of GIS data is improving as remote
sensing technologies advance.
In the model, the optimal vertical alignment is determined
automatically, using the combination of two optimization
techniques: LP method for determining the economic
distribution of cut and fill quantities and SA algorithm for
locating the optimal vertical alignment. LP method guaranties
the global minimum cost for earthwork allocation problem,
while SA provides good/near-optimal solution for the optimal
vertical alignment selection problem.
The results from the brief example were instructive in
presenting how a decision support system equipped with
interactive features, advanced GIS and remote sensing
technologies, and environmental considerations can improve the
design process for forest roads. It provides a road designer with
a number of alternative alignments to evaluate quickly and
systematically. The model has several limitations for further
developments such as improving the graphic interface.
optimizing the horizontal alignment, and calculating earthwork
allocations where the unit costs vary with the quantity of the cut
and fill.
ACKNOWLEDGEMENTS
We would like to thank USDA Forest Services researcher, Steve
Reutebuch, who provided us with LIDAR data of the study
area.
Ending
675 Point
625
S Curve
Beginning Radius: 50.9 m /
600 Point et
Curve ^.
Radius: 62.9 m /
'
Y-Axis (m)
575
550
525
500 —M
215 240 265 290 315 340 365 390 415 440 465 490 515
X-Axis (m)
Figure 5. Plan view of the forest road
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