\name{distmap.owin}
\alias{distmap.owin}
\title{Distance Map of Window}
\description{
  Computes the distance from each pixel to the nearest point
  in the given window.
}
\usage{
  \method{distmap}{owin}(X, \dots)
}
\arguments{
  \item{X}{
    A window (object of class \code{"owin"}).
  }
  \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 an attribute \code{"bdry"}
  which is a pixel image.
}
\details{
  The ``distance map'' of a window \eqn{W} 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{W}.

  This function computes the distance map of the window \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
  pixel in \code{X}.

  Additionally, the return value 
  has an attribute \code{"bdry"} which is 
  also a pixel image. The grey values in \code{"bdry"} give the
  distance from each pixel to the bounding rectangle of the image.

  If the window \code{X} is not already a pixellated window
  (a binary image mask), it is converted into one. The arguments
  \code{...} control the pixel resolution in this case, but will
  otherwise be ignored.
  
  This function is a method for the generic \code{\link{distmap}}.
}
\seealso{
  \code{\link{distmap}},
  \code{\link{distmap.ppp}}
}
\examples{
  data(letterR)
  U <- distmap(letterR)
  \dontrun{
  plot(U)
  plot(attr(U, "bdry"))
  }
}
\author{Adrian Baddeley
  \email{adrian@maths.uwa.edu.au}
  \url{http://www.maths.uwa.edu.au/~adrian/}
  and Rolf Turner
  \email{rolf@math.unb.ca}
  \url{http://www.math.unb.ca/~rolf}
}
\keyword{spatial}