gstat (version 1.0-21)

variogramST: Calculate Spatio-Temporal Sample Variogram

Description

Calculates the sample variogram from spatio-temporal data.

Usage

variogramST(formula, locations, data, ..., tlags = 0:15,  cutoff,
	width = cutoff/15, boundaries = seq(0, cutoff, width),
	progress = interactive(), pseudo = TRUE, assumeRegular=FALSE, na.omit=FALSE)

Arguments

formula

formula, specifying the dependent variable.

locations

A STFDF or STSDF containing the variable; kept for compatibility reasons with variogram, either locations or data must be provided.

data

A STFDF, STSDF or STIDF containing the variable.

...

any other arguments that will be passed to the underlying variogram function. In case of using data of type STIDF, the argument tunit is recommended

tlags

integer; time lags to consider or in case data is of class STIDF the actual temporal boundaries with time unit given by tunit otherwise the same unit as d

cutoff

spatial separation distance up to which point pairs are included in semivariance estimates; as a default, the length of the diagonal of the box spanning the data is divided by three.

width

the width of subsequent distance intervals into which data point pairs are grouped for semivariance estimates, by default the cutoff is divided into 15 equal lags.

boundaries

numerical vector with distance interval upper boundaries; values should be strictly increasing

progress

logical; if TRUE, show text progress bar

pseudo

integer; use pseudo cross variogram for computing time-lagged spatial variograms? -1: find out from coordinates -- if they are equal then yes, else no; 0: no; 1: yes.

assumeRegular

logical; whether the time series should be assumed regular. The first time step is assumed to be representative for the whole series. Note, that temporal lags are considered by index, and no check is made whether pairs actually have the desired sep

na.omit

shall all NA values in the spatio-temporal variogram be dropped? In case where complete rows or columns in the variogram consists of NA only, plot might produce a distorted picture.

Value

• The spatio-temporal sample variogram contains besides the fields np, dist and gamma the spatio-temporal fields, timelag and spacelag, the first of which indicates the time lag used, the second the space lag. spacelag is the midpoint in the spatial lag intervals, whereas dist is the average distance between the point pairs found in a distance interval. To compute variograms for space lag $h$ and time lag $t$, the pseudo cross variogram $(Z_i(s)-Z_{i+t}(s+h))^2$ is averaged over all time lagged observation sets $Z_i$ and $Z_{i+t}$ available (weighted by the number of pairs involved).

References

Cressie, N.A.C., 1993, Statistics for Spatial Data, Wiley.

Cressie, N., C. Wikle, 2011, Statistics for Spatio-temporal Data, Wiley.

http://www.gstat.org/

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

See Also

plot.StVariogram, for variogram models: vgmST, to fit a spatio-temporal variogram model to a spatio-temporal sample variogram: fit.StVariogram

Examples

# The following spatio-temporal variogram has been calcualted through
# vv = variogram(PM10~1, r5to10, width=20, cutoff = 200, tlags=0:5)
# in the vignette "st".

data(vv)
str(vv)
plot(vv)