https://github.com/cran/fields
Tip revision: 48e16d0f1496128e9d29d6f8819092244e94bef0 authored by Doug Nychka on 24 May 2001, 16:33:19 UTC
version 1.1
version 1.1
Tip revision: 48e16d0
as.image.Rd
\name{as.image}
\alias{as.image}
\title{
Creates image from irregular x,y,z
}
\description{
Discretizes a set of 2-d locations to a grid and produces a image object
with the z values in the right cells. For cells with more than one Z
value the average is used.
}
\usage{
as.image(Z, ind, grid=NULL, x=NULL, nrow=64, ncol=64,weights=rep( 1,
length(Z)))
}
\arguments{
\item{Z}{
Values of image
}
\item{ind}{
A matrix giving the row and column subscripts for each image
value in Z. (Not needed if x is specified.)
}
\item{grid}{
A list with components x and y of equally spaced values describing the
centers of the grid points. The default is to use nrow and ncol and the
ranges of the data locations (x) to construct a grid.
}
\item{x}{
Locations of image values. Not needed if ind is specified.
}
\item{nrow}{
Number of rows in image matrix ( x-axis direction)
}
\item{ncol}{
Number of columns in image matrix ( y-axis direction)
}
\item{weights}{
If two or more values fall into the same
pixel a weighted average is used to represent the pixel value. Default is
equal weights.
}
}
\value{
An list in image format with a few more components. Components x and y are
the grid values , z is a
nrow X ncol matrix
with the Z values. NA's are placed at cell locations where Z data has
not been supplied.
Component ind is a 2 column matrix with subscripts for the locations of
the values in the image matrix.
Component N is an image matrix with the number of original values that
fall within each grid box.
Component weights is an image matrix with the sum of the
individual weights for each cell.
}
\details{
The discretization is straightforward once the grid is determined.
If two or more Z values have locations in the same cell the average value
is
taken as the value. See the source code to modify this to get more
information about coincident locations. (See the call to fast.1way)
}
\seealso{
image.smooth, image.plot, Krig.discretize, Krig.replicates, image.count
}
\examples{
# convert precip data to 50X50 image
look<- as.image( precip$y, x= precip$x, nrow=50, ncol=50)
image.plot( look)
# number of obs in each cell.
image.plot( look$x ,look$y, look$N, col=terrain.colors(50))
# hot spot is around Denver
}
\keyword{manip}
% docclass is function
% Converted by Sd2Rd version 1.21.