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

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.

Value

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

Author(s)

Adrian Baddeley adrian@maths.uwa.edu.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner rolf@math.unb.ca http://www.math.unb.ca/~rolf

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)