  In this article we consider the problem of finding the visibility set from a
given point when the obstacles are represented as the level set of a given
function. Although the visibility set can be computed efficiently by ray
tracing, there are advantages to using a level set representation for the
obstacles, and to characterizing the solution using a Partial Differential
Equation (PDE). A nonlocal PDE formulation was proposed in Tsai et. al.
(Journal of Computational Physics 199(1):260-290, 2004): in this article we
propose a simpler PDE formulation, involving a nonlinear obstacle problem. We
present a simple numerical scheme and show its convergence using the framework
of Barles and Souganidis. Numerical examples in both two and three dimensions
are presented.
