Hidden line Elimination: Robert’s Algorithm, Appel’s and Haloed lines Algorithm

Robert’s Algorithm: In this algorithm, back face culling method is used to remove the back facing polygons of a polyhedron. In next phase, remaining edges of polyhedrons are compared that obscure it.

Appel’s Algorithm: This algorithm uses a quantitative invisibility approach. When a line passes behind the front facing polygon its quantitative invisibility is incremented by 1 and when the line passes from behind its quantitative invisibility is decremented by 1. In this approach a term contour lines is used. Contour line is an edge which is shared by a front facing and a back facing polygon.

Haloed lines Algorithm: Haloed lines algorithm is used to suppress all the hidden lines. In this algorithm each line is intersected with those passing in front of it. Then, Section which are obscured by halos are tracked. After that visible sections of each line are drawn. Hidden line elimination is done by checking if halos are wider than spacing between lines.

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