Graphics Reference
In-Depth Information
Projection parall el to
view vecto r direction
Camera
Position
Obje ct in
visible
volume
Ima ge Plane
(near plane)
Object in
v isible
volume
Proj ection parallel to
view vector direction
Figure 14.8.
Orthographic projection.
is defined n units in front of the camera. Along the view vector are two perpendic-
ular planes, the near plane and the far plane . These two planes are n and f units
away from the camera position, respectively.
Both the near and far planes are
W
H units in size. Only objects inside this rectangular volume can participate
in the rendering process.
Just like the image plane, the near plane is perpendicular the view vector. It is
convenient to consider the near plane as the image plane. In computer graphics,
3D objects inside the visible volume are collapsed, or projected, onto the image
plane to form the 2D image.
In computer graphics we always perform orthographic projection when the
visible volume is specified as a rectangular cube. Figure 14.8 shows that for or-
thographic projection, objects inside the rectangular volume are collapsed onto
the near plane along the view vector direction. Notice that in orthographic projec-
tion, as objects move away from the camera, their size does not change. In other
words, a soccer ball right in front of the camera and one 20 meters away will
appear to be the same size on the final image. Obviously, orthographic projection
does not simulate the human vision system, and thus images rendered do not seem
natural and do not appeal to regular users. Orthographic projection is important
for engineering and scientific applications where measurement and relative sizes
of objects are important and must be retained during the rendering process.
×
Tutorial 14.2. Rectangular Visible Volume and Orthographic Projection
Goal. Get experience with the rectangular visible volume and orthographic
projection.
 
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