vertices.Rd
\name{vertices}
\alias{vertices}
\title{Vertices of a Window}
\description{
Finds the vertices of a window
}
\usage{
vertices(w)
}
\arguments{
\item{w}{A window.}
}
\value{
A list with components \code{x} and \code{y} giving the coordinates
of the vertices.
}
\details{
This function computes the vertices (`corners') of a spatial window.
The argument \code{w} should be a window (an object of class
\code{"owin"}, see \code{\link{owin.object}} for details).
If \code{w} is a rectangle, the coordinates of the
four corner points are returned.
If \code{w} is a polygonal window (consisting of one or more
polygons), the coordinates of the vertices of all polygons are
returned.
If \code{w} is a binary mask, then a `boundary pixel' is defined to be
a pixel inside the window
which has at least one neighbour outside the window. The coordinates
of the centres of all boundary pixels are returned.
}
\seealso{
\code{\link{owin.object}}.
}
\examples{
data(letterR)
vert <- vertices(letterR)
plot(letterR, main="Polygonal vertices")
points(vert)
plot(letterR, main="Boundary pixels")
points(vertices(as.mask(letterR)))
}
\author{Adrian Baddeley
\email{Adrian.Baddeley@csiro.au}
\url{http://www.maths.uwa.edu.au/~adrian/}
and Rolf Turner
\email{r.turner@auckland.ac.nz}
}
\keyword{spatial}
\keyword{math}