For the generation of realistic graphics display you know that hidden surfaces and hidden lines should be identified for removing. For this reason we require to conduct visibility tests. Visibility tests try to specify the visible surfaces or visible edges such are visible from a specified viewpoint. Visibility tests are performed via making use of either
Both object-space and image-spaces.
Object-space approaches utilize the directions of a surface normal with respect to a viewing direction to identify a back face. Image-space approaches employ two buffers as: one for storing the pixel intensities and the other for updating the depth of the visible surfaces from the view plane. A method that uses both image-space and object-space employs depth for sorting or reordering of surfaces. In this category this methods also utilize image-space for conducting visibility type tests. While making visibility tests, coherency property is employed to make the method extremely fast.
In this matter, we will discuss three algorithms or methods for detecting visible surfaces as:
Depth-buffer method and Scan-line method come beneath the category of image-space, and area-subdivision method utilizes both image-space and object-space approach.