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the root level of tile has the width and height spans the whole 
globe world. By this means, the area of any node can be 
specified by its east (E) and west (IV) longitude and north (TV) 
and south (5) latitude. For the root node, £ n = 180 
and, N o = -90\S o =9O°. 
Figurel. Multi-Resolution Pyramid model 
The texture tiles are organized in quad-tree structure too (see 
figure2.), which each texture is linked to a unique node in the 
tree and each node is thus associated with a coverage area, or a 
tile. Usually, real-time rendering of massively textured 3D 
scenes involves two major problems: Large numbers of texture 
switches are a well-known performance bottleneck and the set 
of simultaneously visible textures is limited by the graphics 
memory. So it need use different resolution texture to real-time 
render the massively textured scenes. The basic principle of 
multi-resolution texture rendering can be described in: In each 
frame, the texture resolution is chosen in the way that the textel- 
per-pxiel ratio is always near to 1 so that the amount of 
necessary texture data remains small (Henrik Buchholz, 
J. Dollner, 2005). 
Figure2. Structure of the texture quad-tree. 
Each node represents a certain scene part. 
For generating pyramid, each level of pyramid is a single 
storing unit, e.g. a file, and each node of the tree stores a single 
texture image and each texture image of level n is decomposed 
into list of samples containing the colour of R (red), G 
(green),B (blue), and the sample’s location given as latitude (f) 
and longitude X . Depending on the location, each list contains 
the sample is assigned to a list such that each list contains the 
samples of the covered area of one tile at the given resolution 
level n. In addition, each node stores a distance variable which 
represents the minimum distance between the view position and 
the node’s bounding box to ensure that the node’s texture 
resolution is sufficiently high. The scene geometry is stored in 
the leaf node. Each leaf node contains the triangles of its 
corresponding scene part and the related subset of the original 
texture of the input scene. 
In this paper, we introduce mipmap texture into virtual 
environment, just to make it be one part of the pyramid mode 
and choose the appropriate mipmap-level for the corresponding 
area in texture space at runtime. The basic principle of mipmap 
is: the nearer to the viewpoint, the higher resolution texture is 
required, that is when the projected scale of the surface 
increases, interpolation between the original samples of the 
source image is necessary; as the scale is reduced, 
approximation of multiple samples in the source is required. To 
reduce the computation implied by these requirements, a set of 
prefiltered sourced textures may be created and a succession of 
levels which vary the resolution from the original data is 
represented (see figure3.). 
512X256 
Figure3. Various resolution textures of Mip map