\name{as.owin}
\alias{as.owin}
\alias{as.owin.owin}
\alias{as.owin.ppp}
\alias{as.owin.ppm}
\alias{as.owin.quad}
\alias{as.owin.im}
\alias{as.owin.default}
\title{Convert Data To Class owin}
\description{
Converts data specifying an observation window
in any of several formats, into an object of class \code{"owin"}.
}
\usage{
 as.owin(W, \dots, fatal=TRUE)
 \method{as.owin}{owin}(W, \dots, fatal=TRUE)
 \method{as.owin}{ppp}(W, \dots, fatal=TRUE)
 \method{as.owin}{ppm}(W, \dots, fatal=TRUE)
 \method{as.owin}{quad}(W, \dots, fatal=TRUE)
 \method{as.owin}{im}(W, \dots, fatal=TRUE)
 \method{as.owin}{default}(W, \dots, fatal=TRUE)
}
\arguments{
  \item{W}{Data specifying an observation window, in any of several formats
    described under \emph{Details} below.}
  \item{fatal}{Logical flag determining what to do
    if the data cannot be converted to an observation window.
    See Details.
  }
  \item{\dots}{Ignored.}
}
\value{
  An object of class \code{"owin"} (see \code{\link{owin.object}})
  specifying an observation window.
}
\details{
  The class \code{"owin"} is a way of specifying the observation window
  for a point pattern. See \code{\link{owin.object}} for an overview.
 
  This function converts data in any of several formats 
  into an object of class \code{"owin"} for use by the \pkg{spatstat}
  package.  The argument \code{W} may be
  \itemize{
    \item
    an object of class \code{"owin"}
    \item
    a structure with entries \code{xrange}, \code{yrange} specifying the 
    \eqn{x} and \eqn{y} dimensions of a rectangle
    \item
    a four-element vector
    (interpreted as \code{(xmin, xmax, ymin, ymax)})
    specifying the \eqn{x} and \eqn{y} dimensions of a rectangle
    \item
    a structure with entries \code{xl}, \code{xu}, \code{yl}, \code{yu}
    specifying the \eqn{x} and \eqn{y} dimensions of a rectangle
    as \code{(xmin, xmax) = (xl, xu)} and 
    \code{(ymin, ymax) = (yl, yu)}. This will accept objects of
    class \code{spp} used in the Venables and Ripley \code{spatial}
    library.
    \item
    an object of class \code{"ppp"} representing a point pattern.
    In this case, the object's \code{window} structure will be
    extracted.
    \item
    an object of class \code{"quad"} representing a quadrature scheme.
    In this case, the window of the \code{data} component will be
    extracted.
    \item
    an object of class \code{"im"} representing a pixel image.
    In this case, a window of type \code{"mask"} will be returned,
    with the same pixel raster coordinates as the image.
    An image pixel value of \code{NA}, signifying that the pixel
    lies outside the window, is transformed into the logical value
    \code{FALSE}, which is the corresponding convention for window masks.
    \item
    an object of class \code{"ppm"} representing a fitted point process
    model. In this case, \code{as.owin} extracts the  original point
    pattern data to which the model was fitted, and returns the
    observation window of this point pattern. 
  }
  If the argument \code{W} is not in one of these formats
  and cannot be converted to a window, then an error will
  be generated (if \code{fatal=TRUE}) or a value of \code{NULL}
  will be returned (if \code{fatal=FALSE}).

  The function \code{as.owin} is generic, with methods for
  \code{"owin"},
  \code{"im"} and
  \code{"ppp"} as well as the default method.
}
\seealso{
  \code{\link{owin.object}},
  \code{\link{owin}}
}
\examples{
 w <- as.owin(c(0,1,0,1))
 w <- as.owin(list(xrange=c(0,5),yrange=c(0,10)))
 # point pattern
 data(demopat)
 w <- as.owin(demopat)
 # image
 Z <- as.im(function(x,y) { x + 3}, unit.square())
 w <- as.owin(Z)

 # Venables & Ripley 'spatial' package
 require(spatial)
 towns <- ppinit("towns.dat")
 w <- as.owin(towns)
 detach(package:spatial)
}
\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{manip}