LR-visibility in Polygons.
Gautam Das, Paul J. Heffernan, Giri Narasimhan · Canadian Conference on Computational Geometry · 1993
We give a linear-time algorithm which, for a simple polygon P, computes all pairs of points s and t on P that admit LR-visibility. The points s and t partition P into two subchains. We say that P is LR-visible with respect to s and t if each point of P on the chain from s to t is visible from some point of the chain from t to s and vice-versa.