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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
Secondly, road network N’ , is generated from the road 
polygons by Network Generator, as equation (3). To generate 
road networks, a centreline, the skeleton connected two 
intersections of a road polygon, is calculated for each road 
polygon, and all centrelines are topologically connected to 
generate road network consecutively. As the attribute of each 
centreline, the width of the corresponding road polygon is also 
calculated in Network Generator. At last, Building 
Generalization works to cluster and aggregate the original 
building polygons and to simplify both aggregated buildings 
and left original building polygons to form generated building 
A ant . In this unit, the road network created above is used as 
the constraints to separate the original buildings. 
Some details of the proposed framework are discussed with the 
corresponding processed results in the following subsections. 
2.3 To Detect Intersections 
[n our experiments, an intersection is actually defined by one or 
more connected triangles, where three edges of every triangle 
are not original road edges. Here, The triangles are parts of the 
created TIN from the original road edges in Road Modeler. 
Figure 2 shows some detected intersections from a set of real 
road edges. Here, the regions between each pair of intersections 
are road regions. 
a e y 
dy Wd 
By age 
ed x 
: = tn rt 
x re : : |l 
4 Z4 P 
Figure 2. Samples of Detected Intersections 
Intersections = filled regions, 
road regions = ranges between each pair of intersections 
2.4 To Create Road Polygons by Connecting Road Areas 
Generally, there are three or more road regions around an 
intersection. |o connect two principal road regions, probability 
connection. function between two regions is introduced as 
follow. 
PCR. A) = AD = Dj - 9e mod90 
i2; . 
  
90 (5) 
W, -w,| 
+ -— ALL 
W,W, 
25(4, ^ A;) 
YS S4) 
where, [) —[- 90,90), direction of A, 
W, — width of A, 
251 
S(A)=areaof A 
Osa,DB,ysland o-f*y-l 
&,fB and y are weights for direction, width and overlapped 
area between two road regions to be checked, respectively. 
Here, the width and direction of the rectangle are equal to those 
of the corresponding road region, and the length is an external 
parameter. Moreover, a boundary rectangle is created for each 
road region at the borderline between the intersection and the 
corresponding road region. Then, the overlapped area between 
two road regions means their common region. Figure 3 shows 
some overlapped boundary rectangles. With equation (5), the 
pairs of road regions to be connected are obtained and shown in 
figure 4. 
  
Figure 4. Pairs of Road Areas: There are two green triangles for 
each intersection. Two road regions including green 
triangles will be merged as a road polygon. 
2.5 To Create Road Network 
Two steps are introduced to create road network from 
road polygons. One is creating centerlines for all road 
polygons, and the other is extending the centerlines to 
generate road networks. Both steps are implemented in 
Network Generator. À centerline is created by connecting 
the middle points of inner edges of all triangles one by 
one for a road polygon. Here, the created centerlines are 
not connected with each other, because each centerline is 
limited to the inner range of the corresponding road 
polygon. Road network is created by extending each 
centerline to the centerlines of connected road polygons. 
Figure 5 shows the created road networks overlapped