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% file spatial/man/trls.influence.Rd
% copyright (C) 2001-2 W. N. Venables and B. D. Ripley
%
\name{trls.influence}
\alias{trls.influence}
\alias{plot.trls}
\title{
Regression diagnostics for trend surfaces
}
\description{
This function provides the basic quantities which are used in
forming a variety of diagnostics for checking the quality of
regression fits for trend surfaces calculated by \code{surf.ls}.
}
\usage{
trls.influence(object)
\method{plot}{trls}(x, border = "red", col = NA, pch = 4, cex = 0.6,
add = FALSE, div = 8, \dots)
}
\arguments{
\item{object, x}{
Fitted trend surface model from \code{surf.ls}
}
\item{div}{
scaling factor for influence circle radii in \code{plot.trls}
}
\item{add}{
add influence plot to existing graphics if \code{TRUE}
}
\item{border, col, pch, cex, \dots}{
additional graphical parameters
}
}
\value{
\code{trls.influence} returns a list with components:
\item{r}{
raw residuals as given by \code{residuals.trls}
}
\item{hii}{
diagonal elements of the Hat matrix
}
\item{stresid}{
standardised residuals
}
\item{Di}{
Cook's statistic
}
}
\references{
Unwin, D. J., Wrigley, N. (1987) Towards a general-theory of
control point distribution effects in trend surface models.
\emph{Computers and Geosciences,} \bold{13}, 351--355.
Venables, W. N. and Ripley, B. D. (2002)
\emph{Modern Applied Statistics with S.} Fourth edition. Springer.
}
\seealso{
\code{\link{surf.ls}}, \code{\link{influence.measures}}, \code{\link{plot.lm}}
}
\examples{
library(MASS) # for eqscplot
data(topo, package = "MASS")
topo2 <- surf.ls(2, topo)
infl.topo2 <- trls.influence(topo2)
(cand <- as.data.frame(infl.topo2)[abs(infl.topo2$stresid) > 1.5, ])
cand.xy <- topo[as.integer(rownames(cand)), c("x", "y")]
trsurf <- trmat(topo2, 0, 6.5, 0, 6.5, 50)
eqscplot(trsurf, type = "n")
contour(trsurf, add = TRUE, col = "grey")
plot(topo2, add = TRUE, div = 3)
points(cand.xy, pch = 16, col = "orange")
text(cand.xy, labels = rownames(cand.xy), pos = 4, offset = 0.5)
}
\keyword{spatial}
|
