spatstat (version 1.31-3)

bdist.pixels: Distance to Boundary of Window

Description

Computes the distances from each pixel in a window to the boundary of the window.

Usage

bdist.pixels(w, ..., style="image")

Arguments

w

A window (object of class "owin").

...

Arguments passed to as.mask to determine the pixel resolution.

style

Character string determining the format of the output: either "matrix", "coords" or "image".

Value

• If style="image", a pixel image (object of class "im") containing the distances from each pixel in the image raster to the boundary of the window.

  If style="matrix", a matrix giving the distances from each pixel in the image raster to the boundary of the window. Rows of this matrix correspond to the $y$ coordinate and columns to the $x$ coordinate. If style="coords", a list with three components x,y,z, where x,y are vectors of length $m,n$ giving the $x$ and $y$ coordinates respectively, and z is an $m \times n$ matrix such that z[i,j] is the distance from (x[i],y[j]) to the boundary of the window. Rows of this matrix correspond to the $x$ coordinate and columns to the $y$ coordinate. This result can be plotted with persp, image or contour.

Details

This function computes, for each pixel $u$ in the window w, the shortest distance $d(u, W^c)$ from $u$ to the boundary of $W$.

If the window is not of type "mask" then it is first converted to that type. The arguments "..." are passed to as.mask to determine the pixel resolution.

See Also

owin.object, erosion, bdist.points, bdist.tiles.

Examples

u <- owin(c(0,1),c(0,1))
  d <- bdist.pixels(u, eps=0.01)
  image(d)
  d <- bdist.pixels(u, eps=0.01, style="matrix")
  mean(d >= 0.1)
  # value is approx (1 - 2 * 0.1)^2 = 0.64