ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
411 
Figure 2 Surface model of timber component 
3. Simulation of lignification 
In order to generate satisfactory and virtual realistic images of 
a timber building by the computer simulation system, it needs 
to simulate the surface material of each component besides 
the establishment of correct model. This is beginning with the 
generation of material texture. 
3.1 Generating material texture 
The main task of generating material texture is to determine 
the color, texture and light and shade pattern of the material. 
The color of a material can be divided into three categories: 
ambient the color of the shading part of an object, 
diffuse—-the color of an object under lighting, specular—-the 
color of an object under strong lighting. 
Texture describes the natural characteristics of the 
surface of an object, it can be generated by a 2D random 
function f(u,v) Let N(p,a) denotes a normal distribution 
function withprepresents the mean value and crthe standard 
deviation. The method generates f(u,v) is the following: 
/ (« min 
/ (“ min 
/ (“ max 
. / (“ max 
Vmm )= /, = N (0 <x) 
Vmax )= /2 = N(0 a) O) 
v mi „ )= /3 = N (0 a) 
Vmax )= /4 = ^(0 G) 
therefore, the generation of a random function upon the 
interval of [u-min, u-max]*[v-min, v_max] can be decomposed 
to the generation of 4 random functions upon 4 sub-intervals 
derived from the segmentation of the whole interval into 4 parts, 
with the cut-off point on (....). A recursive process is applied by 
using the abovementioned algorithm until the detail of the 
generated texture is satisfactory enough. According to the 
formula listed in equation 1 and 2, the standard deviation is