R: Spokes pattern of dummy points

spokes {spatstat.geom} | R Documentation

## Spokes pattern of dummy points

### Description

Generates a pattern of dummy points in a window, given a data point pattern. The dummy points lie on the radii of circles emanating from each data point.

### Usage

     spokes(x, y, nrad = 3, nper = 3, fctr = 1.5, Mdefault = 1)

### Arguments

`x` | Vector of x coordinates of data points, or a list with components `x` and `y`, or a point pattern (an object of class `ppp`).
`y` | Vector of y coordinates of data points. Ignored unless `x` is a vector.
`nrad` | Number of radii emanating from each data point.
`nper` | Number of dummy points per radius.
`fctr` | Scale factor. Length of largest spoke radius is `fctr * M` where `M` is the mean nearest neighbour distance for the data points.
`Mdefault` | Value of `M` to be used if `x` has length 1.

### Details

This function is useful in creating dummy points for quadrature schemes (see `quadscheme`).

Given the data points, the function creates a collection of `nrad * nper * length(x)` dummy points.

Around each data point `(x[i],y[i])` there are `nrad * nper` dummy points, lying on `nrad` radii emanating from `(x[i],y[i])`, with `nper` dummy points equally spaced along each radius.

The (equal) spacing of dummy points along each radius is controlled by the factor `fctr`. The distance from a data point to the furthest of its associated dummy points is `fctr * M` where `M` is the mean nearest neighbour distance for the data points.

If there is only one data point the nearest neighbour distance is infinite, so the value `Mdefault` will be used in place of `M`.

If `x` is a point pattern, then the value returned is also a point pattern, which is clipped to the window of `x`. Hence there may be fewer than `nrad * nper * length(x)` dummy points in the pattern returned.

### Value

If argument `x` is a point pattern, a point pattern with window equal to that of `x`. Otherwise a list with two components `x` and `y`. In either case the components `x` and `y` of the value are numeric vectors giving the coordinates of 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`, `inside.owin`, `gridcentres`, `stratrand`

### Examples

      dat <- runifrect(10)
      dum <- spokes(dat$x, dat$y, 5, 3, 0.7)
      plot(dum)
      Q <- quadscheme(dat, dum, method="dirichlet")
      plot(Q, tiles=TRUE)

[Package spatstat.geom version 2.3-2 Index]