Algorithms used for removal of hidden line:

Algorithms that are applied to a set of objects to remove hidden parts to create a more realistic image are usually classified into hidden line and hidden surface algorithms. The former supports line-drawing devices such as vector displays and plotters, while the latter supports raster displays.

The algorithms used for removal of hidden line and hidden surfaces are broadly classified according to whether they deal with object definitions directly or with their projected images. These two approaches are respectively called as object-space methods and image-space methods. An object-space technique compares objects and parts of objects to each other within the scene definition to determine which surfaces, as entire, we must label as visible. In an image-space algorithm, visibility is decided point by point at each pixel position on the projection plane. Most of the visible-surface algorithms use image-space methods, although object-space methods may be used effectively to locate visible surfaces in some of the cases. Line-display algorithms, alternatively in general use object-space methods to identify visible lines in wire-frame displays, but several image-space visible-surface algorithms can be adapted easily to visible-line detection.