gstat (version 2.0-3)

vgm: Generate, or Add to Variogram Model

Description

Generates a variogram model, or adds to an existing model. print.variogramModel prints the essence of a variogram model.

Usage

vgm(psill = NA, model, range = NA, nugget, add.to, anis, kappa = 0.5, ..., covtable,
	Err = 0)
# S3 method for variogramModel
print(x, ...)
# S3 method for variogramModel
plot(x, cutoff, ..., type = 'l')
as.vgm.variomodel(m)

Arguments

psill

(partial) sill of the variogram model component, or model: see Details

model

model type, e.g. "Exp", "Sph", "Gau", "Mat". Calling vgm() without a model argument returns a data.frame with available models.

range

range parameter of the variogram model component; in case of anisotropy: major range

kappa

smoothness parameter for the Matern class of variogram models

nugget

nugget component of the variogram (this basically adds a nugget compontent to the model); if missing, nugget component is omitted

add.to

the variogram model to which we want to add a component (structure)

anis

anisotropy parameters: see notes below

x

a variogram model to print or plot

...

arguments that will be passed to print, e.g. digits (see examples), or to variogramLine for the plot method

covtable

if model is Tab, instead of model parameters a one-dimensional covariance table can be passed here. See covtable.R in tests directory, and example below.

Err

numeric; if larger than zero, the measurement error variance component that will not be included to the kriging equations, i.e. kriging will now smooth the process Y instead of predict the measured Z, where Z=Y+e, and Err is the variance of e

m

object of class variomodel, see geoR

cutoff

maximum distance up to which variogram values are computed

type

plot type

Value

If a single model is passed, an object of class variogramModel extending data.frame.

In case a vector ofmodels is passed, an object of class variogramModelList which is a list of variogramModel objects.

When called without a model argument, a data.frame with available models is returned, having two columns: short (abbreviated names, to be used as model argument: "Exp", "Sph" etc) and long (with some description).

as.vgm.variomodel tries to convert an object of class variomodel (geoR) to vgm.

Details

If only the first argument (psill) is given a character value indicating a model, as in vgm("Sph"), then this taken as a shorthand form of vgm(NA,"Sph",NA,NA), i.e. a spherical variogram with nugget and unknown parameter values; see examples below. Read fit.variogram to find out how NA variogram parameters are given initial values for a fitting a model, based on the sample variogram. Package automap gives further options for automated variogram modelling.

References

http://www.gstat.org/

Pebesma, E.J., 2004. Multivariable geostatistics in S: the gstat package. Computers \& Geosciences, 30: 683-691.

Deutsch, C.V. and Journel, A.G., 1998. GSLIB: Geostatistical software library and user's guide, second edition, Oxford University Press.

For the validity of variogram models on the sphere, see Huang, Chunfeng, Haimeng Zhang, and Scott M. Robeson. On the validity of commonly used covariance and variogram functions on the sphere. Mathematical Geosciences 43.6 (2011): 721-733.

See Also

show.vgms to view the available models, fit.variogram, variogramLine, variogram for the sample variogram.

Examples

# NOT RUN {
vgm()
vgm("Sph")
vgm(NA, "Sph", NA, NA)
vgm(, "Sph") # "Sph" is second argument: NO nugget in this case
vgm(10, "Exp", 300)
x <- vgm(10, "Exp", 300)
vgm(10, "Nug", 0)
vgm(10, "Exp", 300, 4.5)
vgm(10, "Mat", 300, 4.5, kappa = 0.7)
vgm( 5, "Exp", 300, add.to = vgm(5, "Exp", 60, nugget = 2.5))
vgm(10, "Exp", 300, anis = c(30, 0.5))
vgm(10, "Exp", 300, anis = c(30, 10, 0, 0.5, 0.3))
# Matern variogram model:
vgm(1, "Mat", 1, kappa=.3)
x <- vgm(0.39527463, "Sph", 953.8942, nugget = 0.06105141)
x
print(x, digits = 3);
# to see all components, do
print.data.frame(x)
vv=vgm(model = "Tab",  covtable = 
	variogramLine(vgm(1, "Sph", 1), 1, n=1e4, min = 0, covariance = TRUE))
vgm(c("Mat", "Sph"))
vgm(, c("Mat", "Sph")) # no nugget
# }