R: Resample a Point Pattern by Resampling Quadrats

quadratresample {spatstat} | R Documentation

## Resample a Point Pattern by Resampling Quadrats

### Description

Given a point pattern dataset, create a resampled point pattern by dividing the window into rectangular quadrats and randomly resampling the list of quadrats.

### Usage

    quadratresample(X, nx, ny=nx, ...,
                    replace = FALSE, nsamples = 1,
                    verbose = (nsamples > 1))

### Arguments

`X` | A point pattern dataset (object of class `"ppp"`).
`nx,ny` | Numbers of quadrats in the x and y directions.
`...` | Ignored.
`replace` | Logical value. Specifies whether quadrats should be sampled with or without replacement.
`nsamples` | Number of randomised point patterns to be generated.
`verbose` | Logical value indicating whether to print progress reports.

### Details

This command implements a very simple bootstrap resampling procedure for spatial point patterns `X`.

The dataset `X` must be a point pattern (object of class `"ppp"`) and its observation window must be a rectangle.

The window is first divided into `N = nx * ny` rectangular tiles (quadrats) of equal size and shape. To generate one resampled point pattern, a random sample of `N` quadrats is selected from the list of `N` quadrats, with replacement (if `replace=TRUE`) or without replacement (if `replace=FALSE`). The ith quadrat in the original dataset is then replaced by the ith sampled quadrat, after the latter is shifted so that it occupies the correct spatial position. The quadrats are then reconstituted into a point pattern inside the same window as `X`.

If `replace=FALSE`, this procedure effectively involves a random permutation of the quadrats. The resulting resampled point pattern has the same number of points as `X`. If `replace=TRUE`, the number of points in the resampled point pattern is random.

### Value

A point pattern (if `nsamples = 1`) or a list of point patterns (if `nsamples > 1`).

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au

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

### See Also

`quadrats`, `quadratcount`.

See `varblock` to estimate the variance of a summary statistic by block resampling.

### Examples

      data(bei)
      quadratresample(bei, 6, 3)

[Package spatstat version 1.54-0 Index]