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\name{LakeAcidity}
\alias{LakeAcidity}
\title{Water Acidity in Lakes}
\description{
Data extracted from the Eastern Lake Survey of 1984 conducted by the
United States Environmental Protection Agency, concerning 112 lakes
in the Blue Ridge.
}
\usage{data(LakeAcidity)}
\format{
A data frame containing 112 observations on the following variables.
\tabular{ll}{
\code{ph} \tab Surface ph.\cr
\code{cal} \tab Calcium concentration.\cr
\code{lat} \tab Latitude.\cr
\code{lon} \tab Longitude.\cr
\code{geog} \tab Geographic location, derived from \code{lat}
and \code{lon}
}
}
\details{
\code{geog} was generated from \code{lat} and \code{lon} using the
code given in the Example section.
}
\source{
Douglas, A. and Delampady, M. (1990), \emph{Eastern Lake Survey --
Phase I: Documentation for the Data Base and the Derived Data
sets.} Tech Report 160 (SIMS), Dept. Statistics, University of
British Columbia.
}
\references{
Gu, C. and Wahba, G. (1993), Semiparametric analysis of variance
with tensor product thin plate splines. \emph{Journal of the Royal
Statistical Society Ser. B}, \bold{55}, 353--368.
}
\examples{
## Converting latitude and longitude to x-y coordinates
\dontrun{ltln2xy <- function(latlon,latlon0) {
lat <- latlon[,1]*pi/180; lon <- latlon[,2]*pi/180
lt0 <- latlon0[1]*pi/180; ln0 <- latlon0[2]*pi/180
x <- cos(lt0)*sin(lon-ln0); y <- sin(lat-lt0)
cbind(x,y)
}
data(LakeAcidity)
latlon <- as.matrix(LakeAcidity[,c("lat","lon")])
m.lat <- (min(latlon[,1])+max(latlon[,1]))/2
m.lon <- (min(latlon[,2])+max(latlon[,2]))/2
ltln2xy(latlon,c(m.lat,m.lon))
## Clean up
rm(ltln2xy,LakeAcidity,latlon,m.lat,m.lon)}
}
\keyword{datasets}
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