It "is “necessary now to render the
terrain, using Computer Graphic
techniques. It must be made a choice
between a fast methods and methods that
produce more realistic effects.
Figures 3.7 to 3.9 show the sequence to
the rendering of the terrain. For hidden
lines it was used the Z-buffer algorithm,
and for illumination the Gouraud
technique. The illumination was computed
by the following formula:
Vetor
Normal
Vetor de
Visualizacáo
Ia Ci. cos (a) Ic + Ta,
where Ia is the light intensity reflected
in each RGB color, C; is the reflectance
coefficient for the material for each RGB
color, cos(a) is the cosine of the angle
formed by the normal and the incident
light, 1: is the intensity of the Light
source in each RGB color, and I, is the
ambient light. Using Gouraud, the
intensities inside each point in the
triangles is the linear interpolation of
the vertices intensities.
Fig. 3.7 - Vector Normal to the plane.
Ponto de
lluminacáo
lluminaçäo
Ambiente
Fig. 3.8 - Vectors between a illumination point and triangle
vertices.
Fig. 3.9 - Painting sequence with the Z-Buffer algorithm de o Z-
Buffer.
The last step is the painting of each
polygon, through gray levels. Tt is
; : | possible to use more sophisticated
Next, the conic perspective projection methods as fractals, or an airplane or
has to be performed. Figure 3.10 presents satellite image, however due to the need
the steps for the calculation of a for speed in the computer calculations in
conical perspective projection, with the this work the gray levels were painted
reduction from three to two dimensions.
911
according to their light intensity, from
0 (black) to 255 (white) in each RGB
color.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996