R: Generate a Default Pattern of Dummy Points

default.dummy {spatstat} | R Documentation

## Generate a Default Pattern of Dummy Points

### Description

Generates a default pattern of dummy points for use in a quadrature scheme.

### Usage

     default.dummy(X, nd, random=FALSE, ntile=NULL, npix=NULL,
                  quasi=FALSE, ..., eps=NULL, verbose=FALSE)

### Arguments

`X` | The observed data point pattern. An object of class `"ppp"` or in a format recognised by `as.ppp()`
`nd` | Optional. Integer, or integer vector of length 2, specifying an `nd * nd` or `nd[1] * nd[2]` rectangular array of dummy points.
`random` | Logical value. If `TRUE`, the dummy points are generated randomly.
`quasi` | Logical value. If `TRUE`, the dummy points are generated by a quasirandom sequence.
`ntile` | Optional. Integer or pair of integers specifying the number of rows and columns of tiles used in the counting rule.
`npix` | Optional. Integer or pair of integers specifying the number of rows and columns of pixels used in computing approximate areas.
`...` | Ignored.
`eps` | Optional. Grid spacing. A positive number, or a vector of two positive numbers, giving the horizontal and vertical spacing, respectively, of the grid of dummy points. Incompatible with `nd`.
`verbose` | If `TRUE`, information about the construction of the quadrature scheme is printed.

### Details

This function provides a sensible default for the dummy points in a quadrature scheme.

A quadrature scheme consists of the original data point pattern, an additional pattern of dummy points, and a vector of quadrature weights for all these points. See `quad.object` for further information about quadrature schemes.

If `random` and `quasi` are both false (the default), then the function creates dummy points in a regular `nd[1]` by `nd[1]` rectangular grid. If `random` is true and `quasi` is false, then the frame of the window is divided into an `nd[1]` by `nd[1]` array of tiles, and one dummy point is generated at random inside each tile. If `quasi` is true, a quasirandom pattern of `nd[1] * nd[2]` points is generated. In all cases, the four corner points of the frame of the window are added. Then if the window is not rectangular, any dummy points lying outside it are deleted.

If `nd` is missing, a default value (depending on the data pattern `X`) is computed by `default.ngrid`.

Alternative functions for creating dummy patterns include `corners`, `gridcentres`, `stratrand` and `spokes`.

### Value

A point pattern (an object of class `"ppp"`, see `ppp.object`) containing the dummy points.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au

and Rolf Turner r.turner@auckland.ac.nz

### See Also

`quad.object`, `quadscheme`, `corners`, `gridcentres`, `stratrand`, `spokes`

### Examples

      data(simdat)
      P <- simdat
      D <- default.dummy(P, 100)
      ## Not run: plot(D)
      Q <- quadscheme(P, D, "grid")
      ## Not run: plot(union.quad(Q))

[Package spatstat version 1.63-3 Index]