asr_varioGram {asreml} | R Documentation

## Empirical variogram.

### Description

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, Oliver MA (2001). Geostatistics for Environmental Scientists. John Wiley: West Sussex.

[Package asreml version 4.1.0.176 Index]