International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
  
polygons. Displacement of building polygons is also considered 
in clustering procedure by using the created road networks to 
separate building polygons. 
In the following sections, we give an overview of the proposed 
framework firstly and discuss the details of some algorithms in 
the framework in section 2. Section 3 gives some experimental 
results to verify the effectiveness of the proposed method. And 
section 4 concludes the paper with some discussions. 
2. FRAMEWORK AND ALGORITHM 
2.1 Notations and Definitions 
Some notations used in this paper are listed below. 
Ms Point set representing obj 
Lo Line set representing op; 
Me Area (polygon) set representing opj 
M ut Network (topologically connected lines) set 
representing obj 
Tu Triangle set representing obj 
TIN(X): Function creating TIN (Triangulated Irregular 
Network) from X 
T: zi ete. NV Triangle set 
In this paper, we only discuss the generalization of road edges 
and building polygons. Let [,., be original road edges, and 
rodac 
A original building polygons. Then, the original map 
dataset may be represented as follows. 
building 
i road ? A building f dE 
Furthermore, a notation without an apostrophe (’) means an 
original datum or object, such as road edges [ mentioned 
E ro 
above, otherwise, a created/output datum or object. 
For the convenience of the following explanation, we also 
clarify some key words as follows. 
Line representing the right or left 
side / boundary of the original road 
data. 
Polygons representing the original 
building data. 
Road region: The range between two 
intersections, excluding any 
intersections and inside a road. 
Range connected by more than two 
road regions. 
A single road region or connected 
road regions, the first output dataset 
A’ in this paper. Road polygons 
Road edge: 
Building polygon: 
Intersection: 
Road polygon: 
are also connected with each other to 
cover the entire road. 
Centerline: Line representing the 
skeleton of a road polygon. 
Topologically connected centerlines, 
central 
Road network: 
50 
the second output dataset N' , in 
rende 
this paper. As compared to road 
centerlines, road network 
emphasizes the topological 
characteristics of the road data. 
Polygon merged by more than one 
building polygons. 
The third output dataset, 4’ 
building 
Aggregated building: 
Generalized building: 
generalized building is a polygon 
obtained by simplifying an 
aggregated building or an original 
building polygon, which was not 
aggregated. 
2.2 Framework 
The proposed framework is shown in Figure 1. Here, road 
generalization includes two units: Road Modeler and Network 
Generator (Wang, 2002, Wang, 2003). The input data is a set of 
road edges [and building polygons 4 , and the output 
rodc 
building 
includes three datasets: road polygons 4’ (result of Road 
Modeler), road network A” 2 (result of Network Generator), 
; (result of Building 
and generalized buildings 7... 
uilding > 
Generalization). Here, Road polygons is used to create road 
network inside the Road Generalization unit, and can also be 
outputted as modeled road data for some GIS systems too. Road 
network is also used as constraints for generalizing buildings in 
Building Generalization unit. The framework can also be 
represented as follows. 
A. ={T =TIN(L,,,)|T, is inside the road area] (2) 
roa 
. . ~ A 
N°, = topologically connected centerlines of 47,, — (5) 
Aj, ^ aggregated 4,,,,,, with constraints of N°, 0 
ATE 
i24 Road foc 
i. Modeler - 
     
Road Polygons 
À 
Road Edges 
brit 
vad 
  
ATER 
  
Network 
05 Generator - 
  
  
  
  
Road DE 1 : 
Road Networks 
N° 
——————————————-—- road 
ACIER RSR 
Es ‘Building S m 
Generalization 
% ts 
  
  
  
  
  
   
   
Generalized Buildings 
Arising 
Building Polygons 
Figure 1. Framework for Generalizing Roads and Buildings 
The proposed method works as follows. Firstly, the original 
road edges are modeled as road polygons 4’ , by Road 
T road "Od 
Modeler, as shown in equation (2). Here, a TIN is created by 
using road edges as constraints and analysed to merge the 
triangles inside the road range to generate road polygons. 
Intern 
Secon 
polyg 
road 
intersé 
polyg 
gener: 
centre 
calcul 
Gener 
buildi 
and le 
A! 
buildin 
the co 
Some 
corres 
23 1 
In our 
more 
are no 
create 
Figure 
road e 
are ro: 
Figure 
] 
; 
24 T 
(ICHRT 
interse 
connex 
follow 
PCF 
where,