spatstat (version 1.3-2)

# spokes: 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)`

## Arguments

x
Vector of \$x\$ coordinates of data points.
y
Vector of \$y\$ coordinates of data points.
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.

## Value

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

## Details

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

Given the point pattern specified by the vectors `x` and `y`, the function creates a pattern 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.

## See Also

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

## Examples

```library(spatstat)
dat <- runifrect(10)
plot(dat)
dum <- spokes(dat\$x, dat\$y)
points(dum\$x, dum\$y, pch=".")
Q <- quadscheme(dat, dum)```