Zuxun Zhang
4.2 Extracting the Surface Texture of the House
In object space, each surface of the house consists of TIN. The original image contained in each triangle of the house's
TIN corresponds to the triangles' texture of the visible surface TIN in 3D object-space.
In OpenGL and 3D studio, after determining 3D coordinates of the vertex of a polygon and its correspondent 2D
coordinates in certain texture piece, a 3D-polygon surface with texture map is constructed. The length and width of the
2D-texture piece must be power series of two, and the texture coordinate adopts normalization relative value (0.0-1.0).
To form a texture map, the paper adopts the following way to designate the 2D texture coordinates of the triangle's
vertex.
Figure 7 shows that point A; B and C are three vertexes of triangles on the invisible sides. The circumscribed rectangle
is determined by their 2D coordinate. And the lengths of the rectangles' sides are extended into the power series of two.
The gray level, or trichromatic value RGB, in the range of the circumscribed rectangle of the triangle ABC are extracted
in the aerial image. Add the texture coordinates of the triangle’s 3 vertexes A, B and C are assigned as A:((xl-
x0)/wt,(y1-y0)/ht);B:((x2-x0)/wt,(y2-y0)/ht);C:((x3-x0)/wt,(y3-y0)/ht).
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Figure 7. 2D texture coordinates of triangle vertexes
Every triangle of the house's 3D-surface TIN is projected into the left and right images. The texture extracting from the
visible triangle with larger areas and to better the boundary extraction of complex housing. Figure 8 and Figure 9 show
the example of reconstruction and visualization of regular houses and their texture from the black-white aerial images,
created by the method mentioned above, and Figure 10 shows a 3D model of urban area from the color aerial images.
Figure 8. Black-white 3D urban model
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M E Ma, ee ot : A
LM Nm A
Figure 10. Color 3D urban model
1020 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000.
