Read a Point Process Object from a File
Read a file in standard format and create a point process object.

Syntax
	ppinit(file)

Input
file    string giving file name

Output
pp object with components `x', `y', `xl', `xu', `yl', `yu'


Details
The file should contain:
the number of points (n)
a header (ignored)
xl xu yl yu scale
x y (repeated n times)

Side effects
Calls `ppregion' to set the domain.

See also
`ppregion'

Example
towns <- ppinit("towns.dat")
par(pty="s")
plot(Kfn(towns, 10), type="b", xlab="distance", ylab="L(t)")