Hidden
surface removal and Line elimination :->
In 3D objects some parts of the objects
are hidden by other parts. Methods used
to remove these hidden parts to create more relative image is called hidden
surface elimination methods.
Hidden surface and line elimination algorithms
are divided into two categories.
# Object
Space Algorithm :->
In these type of algorithms, we compare
objects and parts of objects within the world coordinate scene to determine
which surfaces as whole we label as visible.
These types of algorithms concentrate on geometrical relationships among
objects.
Object space algorithms are used for
hidden line elimination in wireframe displays.
These algorithms perform geometric comparisons with high precision. Due to high precision image can be enlarged
without losing its accuracy. The running
time of these algorithms increases with number of objects. Also cost of these algorithms increases as
the complexity of scene increases.
# Image
Space Algorithm :->
In these algorithms visibility of object
is decided point by point at each pixel position on projection plane.
Image space algorithms are mostly used
for hidden surface elimination. Usually
the precision of image space algorithms is less than object space algorithms. The running time of image space algorithms
increases with increase in complexity of visible parts of image. Cost of these algorithms increases at lesser
rate as compared to cost of object space algorithms.
Most of above mentioned algorithms use
sorting and coherence methods to improve performance. Sorting is used for depth comparisons of
individual surface in a scene. According
to their distance from projection plane.
Coherence methods are used to take advantage of regularity in a scene.
The various
algorithms are as follows :-
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