asr_variogram – Emperical variogram

Description

asr_varioGram calculates the empirical variogram from regular or irregular one or two dimensional data.

Usage

asr_varioGram(x, y, z, composite = TRUE, model = c("empirical"),
metric = c("euclidean", "manhattan"), angle = 0, angle.tol = 180,
nlag = 20, maxdist = 0.5, xlag = NA, lag.tol = 0.5, grid = TRUE)

Arguments

`x`	Numeric vector of x coordinates, may also be a matrix or data frame with 2 or 3 columns. If `ncol(x)` is 3, the columns are taken to be the x and y coordinates and the response (z), respectively. If `ncol(x)` is 2, the columns are taken to be the x coordinates and the response, respectively. In this case the y coordinates are generated as `rep(1,nrow(x))`.
`y`	Numeric vector of y coordinates.
`z`	The response vector.
`composite`	For data on a regular grid. If `TRUE`, the average of the variograms in quadrants (x,y) and (x,-y) is returned. Otherwise, both variograms are returned and identiﬁed as quadrants 1 and 4.
`model`	Can only be “`empirical`” at present.
`metric`	The distance between (x,y) points. Valid measures are “`euclidean`” or “`manhattan`“.
`angle`	A vector of directions. Angles are measured in degrees anticlockwise from the x axis. Default is 0.
`angle.tol`	The angle subtended by each direction. That is, an arc `angle+- angle.tol/2`. Default is 180 which gives an omnidirectional variogram.
`nlag`	The maximum number of lags; default is 20.
`maxdist`	The fraction of the maximum distance to include in the calculation. The default is half the maximum distance in the data.
`xlag`	The width of the lags. If missing, `xlag` is set to `maxdist/nlag`.
`lag.tol`	The distance tolerance. If missing, `lag.tol` is set to `xlag/2`.
`grid`	If `FALSE`, forces polar variograms if (x,y) speciﬁes a regular grid; default is `TRUE`.

Details

For one dimensional data the y coordinates need not be supplied and a vector of ones is generated. The function identiﬁes data on a complete regular array and in such cases only computes polar variograms If grid = FALSE. The data is assumed sorted with the x coordinates changing the fastest; the data is sorted internally if this is not the case.

Value

A data frame including the following components:
`x`	The original x coordinates.
`y`	The original y coordinates.
`gamma`	The variogram estimate.
`distance`	The average distance for pairs in the lag.
`np`	The number of pairs in the lag.
`angle`	Direction if not a regular grid.

References

Webster W and Oliver MA (2001). Geostatistics for Environmental Scientists. John Wiley: West Sussex.

Updated on August 7, 2018

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