For delaunayNetwork, points of X which are neighbours
  in the Delaunay triangulation
  (see delaunay) will be joined by a straight line.
  The result will be returned as a linear network (object of class
  "linnet").
For dirichletNetwork, the Dirichlet tessellation is computed
  (see dirichlet) and the edges of the
  tiles of the tessellation are extracted. This is converted to a linear
  network using as.linnet.psp.