R: Make Periodic Copies of a Spatial Pattern

periodify {spatstat.geom} | R Documentation

## Make Periodic Copies of a Spatial Pattern

### Description

Given a spatial pattern (point pattern, line segment pattern, window, etc) make shifted copies of the pattern and optionally combine them to make a periodic pattern.

### Usage

    periodify(X, ...)
    ## S3 method for class 'ppp'
    periodify(X, nx = 1, ny = 1, ...,
               combine=TRUE, warn=TRUE, check=TRUE,
               ix=(-nx):nx, iy=(-ny):ny,
               ixy=expand.grid(ix=ix,iy=iy))
    ## S3 method for class 'psp'
    periodify(X, nx = 1, ny = 1, ...,
               combine=TRUE, warn=TRUE, check=TRUE,
               ix=(-nx):nx, iy=(-ny):ny,
               ixy=expand.grid(ix=ix,iy=iy))
    ## S3 method for class 'owin'
    periodify(X, nx = 1, ny = 1, ...,
               combine=TRUE, warn=TRUE,
               ix=(-nx):nx, iy=(-ny):ny,
               ixy=expand.grid(ix=ix,iy=iy))

### Arguments

`X` | An object representing a spatial pattern (point pattern, line segment pattern or window).
`nx,ny` | Integers. Numbers of additional copies of `X` in each direction. The result will be a grid of `2 * nx + 1` by `2 * ny + 1` copies of the original object. (Overruled by `ix, iy, ixy`).
`...` | Ignored.
`combine` | Logical flag determining whether the copies should be superimposed to make an object like `X` (if `combine=TRUE`) or simply returned as a list of objects (`combine=FALSE`).
`warn` | Logical flag determining whether to issue warnings.
`check` | Logical flag determining whether to check the validity of the combined pattern.
`ix, iy` | Integer vectors determining the grid positions of the copies of `X`. (Overruled by `ixy`).
`ixy` | Matrix or data frame with two columns, giving the grid positions of the copies of `X`.

### Details

Given a spatial pattern (point pattern, line segment pattern, etc) this function makes a number of shifted copies of the pattern and optionally combines them. The function `periodify` is generic, with methods for various kinds of spatial objects.

The default is to make a 3 by 3 array of copies of `X` and combine them into a single pattern of the same kind as `X`. This can be used (for example) to compute toroidal or periodic edge corrections for various operations on `X`.

If the arguments `nx`, `ny` are given and other arguments are missing, the original object will be copied `nx` times to the right and `nx` times to the left, then `ny` times upward and `ny` times downward, making `(2 * nx + 1) * (2 * ny + 1)` copies altogether, arranged in a grid, centred on the original object.

If the arguments `ix`, `iy` or `ixy` are specified, then these determine the grid positions of the copies of `X` that will be made. For example `(ix,iy) = (1, 2)` means a copy of `X` shifted by the vector `(ix * w, iy * h)` where `w,h` are the width and height of the bounding rectangle of `X`.

If `combine=TRUE` (the default) the copies of `X` are superimposed to create an object of the same kind as `X`. If `combine=FALSE` the copies of `X` are returned as a list.

### Value

If `combine=TRUE`, an object of the same class as `X`. If `combine=FALSE`, a list of objects of the same class as `X`.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au

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

### See Also

`shift`

### Examples

      data(cells)
      plot(periodify(cells))
      a <- lapply(periodify(Window(cells), combine=FALSE),
            plot, add=TRUE,lty=2)

[Package spatstat.geom version 2.2-0 Index]