ramps (version 0.6-12)

corRSpher: Spherical Spatial Correlation Structure

Description

This function is a constructor for the 'corRSpher' class, representing a spherical spatial correlation structure. Letting $r$ denote the range, the correlation between two observations a distance $d < r$ apart is $1-1.5(d/r)+0.5(d/r)^3$. If $d \geq r$ the correlation is zero.

Usage

corRSpher(value = numeric(0), form = ~ 1,
             metric = c("euclidean", "maximum", "manhattan", "haversine"),
             radius = 3956)

Arguments

value

optional numeric range parameter value for the spherical correlation structure, which must be greater than zero. Defaults to numeric(0), which results in a range of 90% of the minimum distance being assigned to the parameter

form

one-sided formula of the form ~ S1+...+Sp, specifying spatial covariates S1 through Sp. Defaults to ~ 1, which corresponds to using the order of the observations in the data as a covariate.

metric

optional character string specifying the distance metric to be used. The currently available options are "euclidean" for the root sum-of-squares of distances; "maximum" for the maximum difference; "manhattan" for t

radius

radius to be used in the haversine formula for great-circle distance. Defaults to the Earth's radius of 3,956 miles.

Value

• An object of class 'corRSpher', also inheriting from class 'corSpatial', representing a spherical spatial correlation structure.

References

Cressie, N.A.C. (1993), Statistics for Spatial Data, J. Wiley & Sons.

Venables, W.N. and Ripley, B.D. (1997) Modern Applied Statistics with S-plus, 2nd Edition, Springer-Verlag.

See Also

corClasses, Initialize.corStruct, summary.corStruct

Examples

sp1 <- corRSpher(form = ~ x + y + z)

spatDat <- data.frame(x = (0:4)/4, y = (0:4)/4)

cs1Spher <- corRSpher(1, form = ~ x + y)
cs1Spher <- Initialize(cs1Spher, spatDat)
corMatrix(cs1Spher)

cs2Spher <- corRSpher(1, form = ~ x + y, metric = "man")
cs2Spher <- Initialize(cs2Spher, spatDat)
corMatrix(cs2Spher)