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Concep of hidden surface removal algorithms in computer graphics.

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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