Level set techniques are numerical techniques for tracking the evolution of interfaces. They rely on two central embeddings; first, the embedding of the interface as the zero level set of a higher dimensional function, and second, the embedding (or extension) of the interface's velocity to this higher dimensional level set function. This paper applies Sethian's Fast Marching Method, which is a very fast technique for solving the eikonal and related equations, to the problem of building fast and appropriate extension velocities for the neighboring level sets. Our choice and construction of extension velocities serves several purposes. First, it provides a way of building velocities for neighboring level sets in the cases where the velocity is defined only on the front itself. Second, it provides a subgrid resolution not present in the standard level set approach. Third, it provides a way to update an interface according to a given velocity field prescribed on the front in such a way that the signed distance function is maintained, and the front is never re-initialized; this is valuable in many complex simulations. In this paper, we describe the details of such implementations, together with speed and convergence tests and applications to problems in visibility relevant to semi-conductor manufacturing and thin film physics.