spatstat (version 1.23-1)

gridcentres: Rectangular grid of points

Description

Generates a rectangular grid of points in a window

Usage

gridcentres(window, nx, ny)

Arguments

window

A window. An object of class owin, or data in any format acceptable to as.owin().

nx

Number of points in each row of the rectangular grid.

ny

Number of points in each column of the rectangular grid.

Value

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

Details

This function creates a rectangular grid of points in the window. The bounding rectangle of the window is divided into a regular $nx \times ny$ grid of rectangular tiles. The function returns the $x,y$ coordinates of the centres of these tiles.

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) and for other miscellaneous purposes.

See Also

quad.object, quadscheme, inside.owin, stratrand

Examples

w <- unit.square()
  xy <- gridcentres(w, 10,15)
  plot(w)
  points(xy)

  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 <- gridcentres(w, 30, 30)
  ok <- inside.owin(xy$x, xy$y, w)
  plot(w)
  points(xy$x[ok], xy$y[ok])