Hidden line removal

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Line removal technique in action

Hidden line removal is an extension of wireframe model rendering where lines (or segments of lines) covered by surfaces are not drawn.

This is not the same as hidden face removal since this involves depth and occlusion while the other involves normals.


A commonly used algorithm to implement it is Arthur Appel's algorithm.[1] This algorithm works by propagating the visibility from a segment with a known visibility to a segment whose visibility is yet to be determined. Certain pathological cases exist that can make this algorithm difficult to implement. Those cases are:

  1. Vertices on edges;
  2. Edges on vertices;
  3. Edges on edges.

This algorithm is unstable because an error in visibility will be propagated to subsequent nodes (although there are ways to compensate for this problem).[2]


  1. ^ (Appel, A., "The Notion of Quantitative Invisibility and the Machine Rendering of Solids", Proceedings ACM National Conference, Thompson Books, Washington, DC, 1967, pp. 387-393.)
  2. ^ James Blinn, "Fractional Invisibility", IEEE Computer Graphics and Applications, Nov. 1988, pp. 77-84.

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