The distance function of a set of points $A$ is the
mathematical function $f$ such that, for any
two-dimensional spatial location $(x,y)$,
the function value f(x,y)
is the shortest distance from $(x,y)$ to $A$. The command f <- distfun(X)
returns a function
in the Rlanguage, with arguments x,y
, that represents the
distance function of X
. Evaluating the function f
in the form v <- f(x,y)
, where x
and y
are any numeric vectors of equal length containing coordinates of
spatial locations, yields the values of the distance function at these
locations.
This should be contrasted with the related command distmap
which computes the distance function of X
on a grid of locations, and returns the distance
values in the form of a pixel image.
The result of f <- distfun(X)
also belongs to the class
"funxy"
and to the special class "distfun"
.
It can be printed and plotted immediately as shown in the Examples.
A distfun
object can be converted to a pixel image
using as.im
.