Linear network (object of class "linnet")
or NULL.
Details
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.