https://github.com/cran/spatstat
Tip revision: 32c7daeb36b6e48fd0356bdcec9580ae124fee5e authored by Adrian Baddeley on 29 December 2015, 22:08:27 UTC
version 1.44-1
version 1.44-1
Tip revision: 32c7dae
imcov.Rd
\name{imcov}
\alias{imcov}
\title{Spatial Covariance of a Pixel Image}
\description{
Computes the unnormalised spatial covariance function of a pixel image.
}
\usage{
imcov(X, Y=X)
}
\arguments{
\item{X}{
A pixel image (object of class \code{"im"}.
}
\item{Y}{
Optional. Another pixel image.
}
}
\value{
A pixel image (an object of class \code{"im"}) representing the
spatial covariance function of \code{X},
or the cross-covariance of \code{X} and \code{Y}.
}
\details{
The (uncentred, unnormalised)
\emph{spatial covariance function} of a pixel image \eqn{X} in the plane
is the function \eqn{C(v)} defined for each vector \eqn{v} as
\deqn{
C(v) = \int X(u)X(u-v)\, {\rm d}u
}{
C(v) = integral of X(u) * X(u-v) du
}
where the integral is
over all spatial locations \eqn{u}, and where \eqn{X(u)} denotes the
pixel value at location \eqn{u}.
This command computes a discretised approximation to
the spatial covariance function, using the Fast Fourier Transform.
The return value is
another pixel image (object of class \code{"im"}) whose greyscale values
are values of the spatial covariance function.
If the argument \code{Y} is present, then \code{imcov(X,Y)}
computes the set \emph{cross-covariance} function \eqn{C(u)}
defined as
\deqn{
C(v) = \int X(u)Y(u-v)\, {\rm d}u.
}{
C(v) = integral of X(u) * Y(u-v) du.
}
Note that \code{imcov(X,Y)} is equivalent to
\code{convolve.im(X,Y,reflectY=TRUE)}.
}
\seealso{
\code{\link{setcov}},
\code{\link{convolve.im}},
\code{\link{owin}},
\code{\link{as.owin}},
\code{\link{erosion}}
}
\examples{
X <- as.im(square(1))
v <- imcov(X)
plot(v)
}
\author{Adrian Baddeley \email{Adrian.Baddeley@curtin.edu.au}
and Rolf Turner \email{r.turner@auckland.ac.nz}
}
\keyword{spatial}
\keyword{math}