distmap.psp.Rd
\name{distmap.psp}
\alias{distmap.psp}
\title{
Distance Map of Line Segment Pattern
}
\description{
Computes the distance from each pixel to the nearest
line segment in the given line segment pattern.
}
\usage{
\method{distmap}{psp}(X, \dots)
}
\arguments{
\item{X}{A line segment pattern (object of class \code{"psp"}).
}
\item{\dots}{Arguments passed to \code{\link{as.mask}}
to control pixel resolution.
}
}
\value{
A pixel image (object of class \code{"im"}) whose greyscale values
are the values of the distance map.
The return value has attributes \code{"index"} and \code{"bdry"}
which are also pixel images.
}
\details{
The ``distance map'' of a line segment pattern \eqn{X} is the function
\eqn{f} whose value \code{f(u)} is defined for any two-dimensional
location \eqn{u} as the shortest distance from \eqn{u} to \eqn{X}.
This function computes the distance map of the line segment pattern \code{X}
and returns the distance map as a pixel image. The greyscale value
at a pixel \eqn{u} equals the distance from \eqn{u} to the nearest
line segment of the pattern \code{X}.
Additionally, the return value
has two attributes, \code{"index"} and \code{"bdry"}, which are
also pixel images. The grey values in \code{"bdry"} give the
distance from each pixel to the bounding rectangle of the image.
The grey values in \code{"index"} are integers identifying which
line segment of \code{X} is closest.
This is a method for the generic function \code{\link{distmap}}.
}
\seealso{
\code{\link{distmap}},
\code{\link{distmap.owin}},
\code{\link{distmap.ppp}}
}
\examples{
a <- psp(runif(20),runif(20),runif(20),runif(20), window=owin())
Z <- distmap(a)
plot(Z)
plot(a, add=TRUE)
}
\author{Adrian Baddeley
\email{adrian@maths.uwa.edu.au}
\url{http://www.maths.uwa.edu.au/~adrian/}
and Rolf Turner
\email{r.turner@auckland.ac.nz}
}
\keyword{spatial}
\keyword{math}