ABSTRACT
The task of Hidden Surface Removal (HSR) is to determine what point will be visible for every pixel of the image plane. Utilizing coherence is a key to building efficient HSR algorithms. Object coherence means that two nearby objects tend to be visible simultaneously. Face coherence implies that if one face of an object is visible then adjacent faces are visible too. Edge coherence means that nearby edges usually belong to the same face or faces that are close to each other and usually have the same visibility. Area coherence means that if some pixel corresponds to a specific face/object then pixels nearby usually also correspond to the same face/object. A major improvement of the z-buffer algorithm utilizing all major types of coherence was proposed by Ned Green, Michael Kass and Gavin Muller in 1993 and called the hierarchical z-buffer.
