International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004 
  
4.Design and Implement of 3D Rendering Engine 
Base on some computer graphics algorithms and 3D GIS 
principles, we designed and implemented an advanced 3D 
visualization engines: PowerCity3D. The graphic API is 
OpenGL. Using PowerCity3D, users can produce a good 
quality of 3D city scene and inquire object information base on 
Access data-base. 
4.1 advanced modeling techniques 
In PowerCity3D, Some advanced graphics algorithms was 
applied. 
(3) Particle systems 
A particle system is defined by a collection of particles that 
evolves over time. The evolution is determined by applying 
certain probabilistic rules to the particles: they may generate 
new particles, they may gain new attributes depending on their 
age, or they may disappear from the scene. They also may move 
according to either deterministic or stochastic laws of motion. 
Each object in particle systems has the following attributes: 
position, velocity, color, lifetime, age, shape, size and 
transparency. In our 3D engine, Particle systems are used to 
model fire, fog, smoke, and water. 
Figure 10 shows the procedure of particle is generated. Figure 
11 shows the fountain based on particle systems in our 3D 
engine. 
  
  
jenerate new particle > Gain new attributes 
  
  
  
  
  
  
Particle die 
: 
Change attributes 
of remain particle 
die 
  
  
  
  
  
Particle rendering 
  
  
  
  
  
  
Figl0 the procedure of particle is generated 
    
Figll particle system model fountain 
(2) Billboard modeling 
Billboard is a new approach for extreme simplification in the 
context of real-time rendering. Using Billboard, 3D models are 
simplified onto a set of planes with texture and transparency 
maps. Xavier use Billboard cloud to simplified 3D model. 
[Xavier 2003]. Aleks realized interactive vegetation 
rendering with a simplified image-based rendering 
approach based solely on alpha-blend textured polygons 
[Aleks 2000]. 
[n this paper, we use billboard to rendering plants, street 
lamps, smoke, buildings and so on. We first replace large 
sets of faces by a texture plane which is generated by 
projecting a texture on a plane (Figure 12). Then we rotate 
the plane to adapt to the viewpoint (Figure 13). 
projecting 
plane 
texture 
  
  
  
  
  
  
  
Figl3(a) Billboard rotate 
b(x Yo 22) 
a : Billboard b 
a(x..y ^ Zi 
^ 1 
Billboard a NN 7 
S X 
e(0,0,0) 
Figl3( b) Billboard rotate in XZ 
Fig13 view-dependent Billboard rotate 
The Q can be defined as: 
o omi X 
Q z 90" — tan! (77) (3) 
Zei 
Where, (x,,y,,z,) isthe Billboard' coordinate. 
Figure 14 shows the billboard rendering in 3D scene.. 
  
      
  
Fig14 Billboard in 3D scene 
   
    
  
  
   
  
  
  
   
   
    
   
   
  
   
  
  
  
  
  
  
  
  
  
  
  
  
  
   
   
  
   
    
    
  
  
  
  
   
  
   
  
  
   
  
  
  
  
  
   
42 
| 
| 
| Inf 
| Be 
inf 
| In 
| ser 
| 3D 
Fig 
fro 
Co 
Th