RRT quickly explores the configuration space, because the
boundary nodes of the tree are more likely selected for the
expansion. The probability that a node will be selected for the
expansion is given by the area of its Voronoi cell (this is called the
Voronoi bias). The nodes located on the boundary of the tree have
larger Voronoi cells, hence they are chosen for the expansion more
frequently than the nodes located inside the tree [41].