As shown in Figure 1, we divide the object into Object2D 
including Vector2D, Grid2D and Object3D including Point3D 
Line3D, Triangle3D. The description of Object2D is same as 
tradition 2D GIS, but the description of Object3D is different. 
Because any space object can be fit by a lot of triangles, so we 
use the Triangle3D take the place of the Area3D in Object3D. 
2.2 Descriptions of Object Models 
Descriptions of space object models always are focus in 3D GIS. 
Object model can be described in several ways: Primitive 
instancing, Spatial enumeration, Cell decomposition, Sweep 
method, Boundary representation (B-Rep), Constructive Solid 
Geometry (CSG)[Zheng 1999]. The two most important type, 
Boundary representation and Constructive Solid Geometry, are 
feasible [Chang 2000]. 
B-Rep describes an object in terms of its surface boundaries, 
vertices, edges, and faces. Some B-Rep are restricted to planar, 
polygonal boundaries, and may even require faces to be convex 
polygons or triangles.[Foley 2002] As shown in Figure 2, we 
define a roof by B-Rep. 
Triangle | 
Triangle 2 
3 
  
  
  
  
(a) primitives 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
  
  
  
  
  
  
  
  
  
  
  
Triangle Array Index Array Vertex Array 
Triangle I KC?'| Index | Vertex | 
—À Triangle 2 N Index 2 ». Vertex 2 
Triangle 3 Index 3 7 Vertex 3 
Triangle 4 Index 4 / Vertex 4 
Index 5 Vertex 5 
nori Index 6 Vertex 6 
Vertex 7 
  
  
Vertex 8 
piri 
  
pugnet 
(b) primitives index 
  
  
  
Fig.2 Description of primitives 
In CSG, simple primitives are combined by means of 
regularized Boolean set operators that are included directly in 
the representation. An object is stored as a tree with operators at 
the internal nodes and simple primitives at the leaves (Figure.3). 
Some nodes represent Boolean operators, whereas others 
perform translation, rotation, and scaling. So we define nine 
primitives: Cylinder, Extrusion, Helix, Polygon, PolygonMesh, 
Revolve, Skin, Sphere and Refer. 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004 
Fig.3 object defined by CSG and its tree 
In this paper, we combine the characteristic of B-Rep and CSG 
by using B-Rep to describe the primitives and using CSG to 
describe the object consisted of some primitives. Figure 4 shows 
some of visualization products defined by CSG and B-Rep. 
  
(a) Build 
  
(b) Tube 
Fig.4 visualization products defined by CSG and B-Rep 
3. Large Scene Accelerate Rendering 
Modern graphics workstations allow the display of thousands of 
shaded or textured polygons at interactive rates. However, many 
applications contain graphical models with geometric 
complexity still greatly exceeding the capabilities of typical 
graphics  hardware.[Lindstrom 1996] This problem is 
particularly prevalent in applications rendering large city 3d 
scene. 
Because there are large datasets that should be rendered in large 
city 3d scene, so we need apply some algorithms to reduce 
datum which need to be rendered and accelerate 3D scene 
rendering and improve the quality of visualization. 
3.1The Accelerate Rendering strategy 
A complete system to display views of large datasets at high 
frame rates consists of components to manage disk paging of 
geometry and texture, level of detail (LOD) selection for texture 
blocks, LOD for triangle geometry, culling to the view frustum, 
and triangle stripping. 
In this paper, we applied Object Culling, Back Face Culling ,