Hidden surface removal:

Hidden surface removal is the most troublesome and most expensive aspect of 3-D computer graphics. Not only is hidden surface removal extremely complex in conceptualization and computation, but this is also very tedious and time-consuming in implementation and processing.

Various approaches to achieve visual realism exist. They are directly related to the types of geometric models utilized to represent three-dimensional objects. Thus, one would expect an upward trend in the efficiency and automation level of these approaches as the geometric modelling techniques have advanced from wire-frames, to surfaces, to solids. Among the existing visualization approaches are parallel projections, perspective projections, hidden line removal, hidden surface removal, hidden solid elimination, and the generation of shaded images of models and scenes.

A wide variety of hidden line and hidden surface removing (visibility) algorithms are in existence today. The development of these algorithms is influenced by the types of graphics display devices they support (whether they are vector or raster) and by the type of data structure or geometric modelling they operate on (wire-frame, surface, or solid modelling). Some algorithms utilize parallel, over the traditional serial, processing to speed up their execution. The formalization and generalization of these algorithms are useful and are required if one attempts to design and build special-purpose hardware to support hidden line and hidden surface removal, which is not restricted to a single algorithm. However, it is not a trivial task to convert the different algorithmic formulations into a form that allows them to be mapped onto a generalized scheme.