R: Stratified random point pattern

stratrand {spatstat} | R Documentation

## Stratified random point pattern

### Description

Generates a “stratified random” pattern of points in a window, by dividing the window into rectangular tiles and placing `k` random points in each tile.

### Usage

     stratrand(window, nx, ny, k = 1)

### Arguments

`window` | A window. An object of class `owin`, or data in any format acceptable to `as.owin()`.
`nx` | Number of tiles in each row.
`ny` | Number of tiles in each column.
`k` | Number of random points to generate in each tile.

### Details

The bounding rectangle of `window` is divided into a regular nx * ny grid of rectangular tiles. In each tile, `k` random points are generated independently with a uniform distribution in that tile.

Note that some of these grid points may lie outside the window, if `window` is not of type `"rectangle"`. The function `inside.owin` can be used to select those grid points which do lie inside the window. See the examples.

This function is useful in creating dummy points for quadrature schemes (see `quadscheme`) as well as in simulating random point patterns.

### Value

A list with two components `x` and `y`, which are numeric vectors giving the coordinates of the random points.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au

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

### See Also

`quad.object`, `quadscheme`, `inside.owin`, `gridcentres`

### Examples

      w <- unit.square()
      xy <- stratrand(w, 10, 10)
      ## Not run:
      plot(w)
      points(xy)

    ## End(Not run)

      # polygonal boundary
      bdry <- list(x=c(0.1,0.3,0.7,0.4,0.2),
                   y=c(0.1,0.1,0.5,0.7,0.3))
      w <- owin(c(0,1), c(0,1), poly=bdry)
      xy <- stratrand(w, 10, 10, 3)
      ## Not run:
      plot(w)
      points(xy)

    ## End(Not run)
      # determine which grid points are inside polygon
      ok <- inside.owin(xy$x, xy$y, w)
      ## Not run:
      plot(w)
      points(xy$x[ok], xy$y[ok])

    ## End(Not run)

[Package spatstat version 1.54-0 Index]