Computes directional variograms for 4 directions provided by the user.
variog4(geodata, coords = geodata$coords, data = geodata$data,
uvec = "default", breaks = "default", trend = "cte", lambda = 1,
option = c("bin", "cloud", "smooth"),
estimator.type = c("classical", "modulus"),
nugget.tolerance, max.dist, pairs.min = 2,
bin.cloud = FALSE, direction = c(0, pi/4, pi/2, 3*pi/4), tolerance = pi/8,
unit.angle = c("radians", "degrees"), messages, ...)The output is an object of the class variog4,
a list with five components.
The first four elements are estimated variograms for the directions
provided and the last is the omnidirectional variogram.
Each individual component is an object of the class variogram,
an output of the function variog.
a list containing element coords
as described next. Typically an object of the class
"geodata" - a geoR data-set.
If not provided the arguments
coords must be provided instead.
an \(n \times 2\) matrix containing
coordinates of the \(n\) data locations in each row.
Defaults to geodata$coords, if provided.
a vector or matrix with data values.
If a matrix is provided, each column is regarded as one variable or realization.
Defaults to geodata$data, if provided.
a vector with values to define the variogram binning. For
further details see documentation for variog.
a vector with values to define the variogram binning. For
further details see documentation for variog.
specifies the mean part of the model.
The options are:
"cte" (constant mean),
"1st" (a first order polynomial
on the coordinates), "2nd" (a second order polynomial
on the coordinates), or a formula of the type ~X where X
is a matrix with the covariates (external trend). Defaults to "cte".
values of the Box-Cox transformation parameter. Defaults to \(1\) (no transformation). If another value is provided the variogram is computed after transforming the data. A case of particular interest is \(\lambda = 0\) which corresponds to log-transformation.
defines the output type: the options "bin" returns values of
binned variogram, "cloud" returns the variogram cloud and
"smooth" returns the kernel smoothed variogram.
Defaults to "bin".
"classical" computes the classical method of
moments estimator. "modulus" returns the variogram
estimator suggested by Hawkins and Cressie (see Cressie, 1993, pg 75).
Defaults to "classical".
a numeric value. Points which are separated by a distance less than this value are considered co-located. Defaults to zero.
a numerical value defining the maximum distance for the variogram. Pairs of locations separated for distance larger than this value are ignored for the variogram calculation. Defaults to the maximum distance among the pairs of data locations.
a integer number defining the minimum numbers of
pairs for the bins.
For option = "bin",
bins with number of pairs smaller than this
value are ignored. Defaults to NULL.
logical. If TRUE and
option = "bin" the cloud values for each class are
included in the output. Defaults to FALSE.
a vector with values of 4 angles, indicating the
directions for which the variograms will be computed. Default
corresponds to c(0, 45, 90, 135) (degrees).
numerical value for the tolerance angle, when computing directional variograms. The value must be in the interval \([0, 90]\) degrees. Defaults to \(\pi/8\).
defines the unit for the specification of angles in
the two previous arguments. Options are "degrees" and "radians".
logical. Indicates whether status messages should be printed on the screen (or output device) while the function is running.
arguments to be passed to the function ksmooth, if
option = "smooth".
Paulo J. Ribeiro Jr. paulojus@leg.ufpr.br,
Peter J. Diggle p.diggle@lancaster.ac.uk.
Further information on the package geoR can be found at:
http://www.leg.ufpr.br/geoR/.
variog for variogram calculations and
plot.variog4 for plotting results
var4 <- variog4(s100, max.dist=1)
plot(var4)
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