Revision d606122dc24b56ecf537d55eda38f4bf5ac4de1f authored by Adrian Baddeley on 25 October 2010, 10:40:51 UTC, committed by cran-robot on 25 October 2010, 10:40:51 UTC
1 parent 66bc933
interp.im.Rd
\name{interp.im}
\alias{interp.im}
\title{Interpolate a Pixel Image}
\description{
Interpolates the values of a pixel image at any
desired location in the frame.
}
\usage{
interp.im(Z, x, y)
}
\arguments{
\item{Z}{
Pixel image (object of class \code{"im"})
with numeric or integer values.
}
\item{x,y}{
Vectors of Cartesian coordinates.
}
}
\details{
A value at each location \code{(x[i],y[i])} will be
interpolated using the pixel values of \code{Z} at the four
surrounding pixel centres, by simple bilinear interpolation.
At the boundary (where \code{(x[i],y[i])} is not surrounded by
four pixel centres) the value at the nearest pixel
is taken.
}
\value{
Vector of interpolated values, with \code{NA} for points that lie
outside the domain of the image.
}
\examples{
opa <- par(mfrow=c(1,2))
# coarse image
V <- as.im(function(x,y) { x^2 + y }, owin(), dimyx=10)
plot(V, main="coarse image", col=terrain.colors(256))
# lookup value at location (0.5,0.5)
V[list(x=0.5,y=0.5)]
# interpolated value at location (0.5,0.5)
interp.im(V, 0.5, 0.5)
# true value is 0.75
# how to obtain an interpolated image at a desired resolution
U <- as.im(interp.im, W=owin(), Z=V, dimyx=256)
plot(U, main="interpolated image", col=terrain.colors(256))
par(opa)
}
\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}
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