A tessellation on a linear network L is a partition of the
network into non-overlapping pieces (tiles). Each tile consists of one
or more line segments which are subsets of the line segments making up
the network. A tile can consist of several disjoint pieces.
This function plots the tessellation on the current device.
It is a method for the generic plot.
If style="segments", each tile is plotted using
segments. Colours distinguish the different
tiles.
If style="image", the tessellation is converted to a pixel
image, and plotted using plot.im.