bul 2004 | International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004 
calculate the model coordinate and complete the information 
      
      
  
  
  
  
    
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
    
  
  
  
'ndering | 
inquire. Figure 17 shows the procedure of inquire coordinate. 
olygons | 1 g P q 
| 4.2 Information inquire in 3D scene 
5 | 
> street 1 . . . . . ~ ~ = 
ce large | Information inquire in 3D scene is one of characters of 3D GIS. 
| by | Because of the complexity of 3D graphics projection, | Model coordinate 
information inquire of 3D GIS is more difficult than 2D GIS. Get View matrix | : (Y y 
e rotate | In this paper, we first obtain the 3D coordinate from the 2D | Obtain DC coordinate | ‚Y,Z) 
| screen coordinate the untransform methods. Then we implement Y (x. y) 
3D information inquire and analysis in 3D scene | = § 
| : or : > a : Model untransform| 
| Figure 15 shows the procedure of coordinate transformation Get model matrix | v 1 
| from model coordinate to screen coordinate. ——€ 
| y get z buffer 
| Get projection Y World coordinate 
matrix : ; sf 
Coordinate untransformt ( x,y z) 
zo“ 
  
  
  
  
  
Fig17 Coordinate inquire 
   
b View 
|-—Coordinate 
M 4.3 3D Rendering Engine 
Projection 
transform 
    
    
i 
1 
: 
3 
3 
According to the 3D rendering algorithms, we design and 
implement 3D rendering engine in OO(oriented object) idea. In 
PowerCity3D, user can use following functions: object 
-— modeling, scene creating and rendering, ramble, advanced 
Figl5 coordinate transform pipeline modeling, collision detection and respond, information inquire 
and analysis based database and so on. Figure 18 shows the 
The transform can be defined as: stroctug af SDensme. 
  
=m mm m ; 
moult utt Scene creating 
  
  
  
  
  
— 
— 
Model data | 
u— u————Ó 
  
  
Where 77, is model transform matrix, 7], is view 
transform matrix, m, is projection transform matrix, M, is 
  
DC transform, matrix, (x, y. zl) is DC homogeneous 
| 
| 
| 
| 
| 
| 
| . . 
coordinate, Z is z buffer, (X,Y,Z,l) is model (C. Advanced modeling 73 View range culling 
| 
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| 
| 
| 
| 
| 
| 
homogeneous coordinate. 
When we inquire information in 3D scene, we can obtain DC 
| coordinate directly from computer screen. If we known the 
| transform matrix, the model coordinate can be obtained by 
untransform. So the key is the transform matrix obtain. Because 
| it is OpenGL API to be used to render the 3D scene, we can 
| obtain these matrixes by matrix stack in which store the 
transform matrix during the procedure of rendering. Figwe 16 | 1 LIII IIlÉlóÓl-l 
| shows the OpenGL matrix stack operation: 
X 
x = 
N X x 
S 
  
     
Input(keyboard_ mouse) 
  
  
| glPushMatrix i t ----—»|g|PopMatrix 
| — bo, 1 : E Fig18 Structure of 3D engine 
  
  
  
  
REI, 
  
  
5.Results and Conclusions 
  
Matrix stack Fe y : | 
Currently, 3D visualization is a hot technology and it be applied 
Fig 16 matrix stack operation in many field. In this paper, we discuss and research some key 
| If the DC ; | f «is k techniques in 3D visualization. Based on these researches, a 3D 
» DC coordinate and trans x is known, we can 3 : ; : ; m 
1e DC continus 20tans ana 1 own e rendering engine PowerCity3D be designed and implemented.