pairs.im.Rd
\name{pairs.im}
\alias{pairs.im}
\title{
Scatterplot Matrix for Pixel Images
}
\description{
Produces a scatterplot matrix of the pixel values
in two or more pixel images.
}
\usage{
\method{pairs}{im}(..., plot=TRUE)
}
\arguments{
\item{\dots}{
Any number of arguments, each of which is either
a pixel image (object of class \code{"im"})
or a named argument to be passed to \code{\link{pairs.default}}.
}
\item{plot}{
Logical. If \code{TRUE}, the scatterplot matrix is plotted.
}
}
\details{
This is a method for the generic function \code{\link{pairs}}
for the class of pixel images.
It produces a square array of plot panels, in which each panel shows
a scatterplot of the pixel values of one image against the
corresponding pixel values of another image.
At least two of the arguments \code{\dots}
should be pixel images (objects of class \code{"im"}).
Their spatial domains must overlap, but need not have the same
pixel dimensions.
First the pixel image domains are intersected, and converted to a
common pixel resolution. Then the corresponding pixel values of each image are
extracted. Then \code{\link{pairs.default}} is called to
plot the scatterplot matrix.
Any arguments in \code{\dots} which are not pixel images will be
passed to \code{\link{pairs.default}} to control the plot.
}
\section{Image or Contour Plots}{
Since the scatterplots may show very dense concentrations of points,
it may be useful to set \code{panel=panel.image}
or \code{panel=panel.contour} to draw a colour image or contour plot
of the kernel-smoothed density of the scatterplot in each panel.
The argument \code{panel} is passed
to \code{\link{pairs.default}}. See the help for
\code{\link{panel.image}} and \code{\link{panel.contour}}.
}
\section{Low Level Control of Graphics}{
To control the appearance of the individual scatterplot panels,
see \code{\link{pairs.default}}, \code{\link{points}}
or \code{\link{par}}.
To control the plotting symbol for the points in the scatterplot,
use the arguments \code{pch}, \code{col}, \code{bg} as described
under \code{\link{points}} (because
the default panel plotter is the function \code{\link{points}}).
To suppress the tick marks on the plot axes,
type \code{par(xaxt="n", yaxt="n")} before calling \code{pairs}.
}
\value{
Invisible. A \code{data.frame} containing the
corresponding pixel values for each image.
The return value also belongs to the class \code{plotpairsim} which has
a plot method, so that it can be re-plotted.
}
\seealso{
\code{\link{pairs}},
\code{\link{pairs.default}},
\code{\link{panel.contour}},
\code{\link{panel.image}},
\code{\link{plot.im}},
\code{\link{im}},
\code{\link{par}}
}
\examples{
X <- density(rpoispp(30))
Y <- density(rpoispp(40))
Z <- density(rpoispp(30))
p <- pairs(X,Y,Z)
p
plot(p)
}
\author{
\spatstatAuthors.
}
\keyword{spatial}
\keyword{hplot}