# periodify

##### Make Periodic Copies of a Spatial Pattern

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 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 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 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`

.

##### See Also

##### Examples

```
# NOT RUN {
data(cells)
plot(periodify(cells))
a <- lapply(periodify(Window(cells), combine=FALSE),
plot, add=TRUE,lty=2)
# }
```

*Documentation reproduced from package spatstat, version 1.63-3, License: GPL (>= 2)*