On a linear network $L$, the geodesic distance function
of a set of points $A$ in $L$ is the
mathematical function $f$ such that, for any
location $s$ on $L$,
the function value f(s)
is the shortest-path distance from $s$ to $A$. The command distfun.lpp
is a method for the generic command
distfun
for the class "lpp"
of point patterns on a linear network.
If X
is a point pattern on a linear network,
f <- distfun(X)
returns a function
in the Rlanguage 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. More efficiently f
can take the arguments
x, y, seg, tp
where seg
and tp
are the local
coordinates on the network.
The function f
obtained from f <- distfun(X)
also belongs to the class "linfun"
.
It can be printed and plotted immediately as shown in the Examples.
It can be
converted to a pixel image using as.linim
.