Tangent visibility analysis for polyhedral models

Visibility analysis is broadly use in process planning for milling process, coordinate measuring machines, and casting processes. However, this type of visibility analysis, which involves determining visibility from a given viewpoint, cannot be applied directly to in-line cutting systems, such as Wire Electrical Discharge Machining (WEDM) or hot wire foam cutter. A new type of visibility analysis, tangent visibility analysis, is required in order to apply visibility result to process planning for in-line cutting systems. The motivation of this paper is to accurately calculate the tangent visibility for objects represented by polygonal surfaces. In this paper, we provide the definition of tangent visibility and discuss the difference between common visibility problem and tangent visibility problem. An algorithm is also developed to calculate the global tangent visibility for a given object. Several polyhedral models are tested to verify the correctness of the tangent visibility algorithm; and the complexity of the algorithm is also discussed.