## The Zermelo-Voronoi Diagram: a Dynamic Partition Problem

##### Abstract

We consider a Voronoi-like partition problem in the plane for a given finite set of generators. Each element in this partition
is uniquely associated with a particular generator in the following sense: An agent that resides within a set of the partition
at a given time will arrive at the generator associated with this set faster than any other agent that resides anywhere outside
this set at the same instant of time. The agent’s motion is affected by the presence of a temporally-varying drift, which is
induced by local winds/currents. As a result, the minimum-time to a destination is not equivalent to the minimum-distance
traveled. This simple fact has important ramifications over the partitioning problem. It is shown that this problem can be
interpreted as a Dynamic Voronoi Diagram problem, where the generators are not fixed, but rather they are moving targets
to be reached in minimum time. The problem is solved by first reducing it to a standard Voronoi Diagram by means of a time-varying coordinate transformation. We then extend the approach to solve the dual problem where the generators are
the initial locations of a given set of agents distributed over the plane, such that each element in the partition consists of the
terminal positions that can be reached by the corresponding agent faster than any other agent.