dilation: Morphological Dilation

Description

Perform morphological dilation of a window, a line segment pattern or a point pattern

Usage

dilation(w, r, ...)
 # S3 method for owin
dilation(w, r, ..., polygonal=NULL, tight=TRUE)
 # S3 method for ppp
dilation(w, r, ..., polygonal=TRUE, tight=TRUE)
 # S3 method for psp
dilation(w, r, ..., polygonal=TRUE, tight=TRUE)

Value

If r > 0, an object of class "owin" representing the dilated region. If r=0, the result is identical to w.

Arguments

w: A window (object of class "owin" or a line segment pattern (object of class "psp") or a point pattern (object of class "ppp").
r: positive number: the radius of dilation.
...: extra arguments passed to as.mask controlling the pixel resolution, if the pixel approximation is used; or passed to disc if the polygonal approximation is used.
polygonal: Logical flag indicating whether to compute a polygonal approximation to the dilation (polygonal=TRUE) or a pixel grid approximation (polygonal=FALSE).
tight: Logical flag indicating whether the bounding frame of the window should be taken as the smallest rectangle enclosing the dilated region (tight=TRUE), or should be the dilation of the bounding frame of w (tight=FALSE).

Author

Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner rolfturner@posteo.net and Ege Rubak rubak@math.aau.dk

Details

The morphological dilation of a set \(W\) by a distance \(r > 0\) is the set consisting of all points lying at most \(r\) units away from \(W\). Effectively, dilation adds a margin of width \(r\) onto the set \(W\).

If polygonal=TRUE then a polygonal approximation to the dilation is computed. If polygonal=FALSE then a pixel approximation to the dilation is computed from the distance map of w. The arguments "\dots" are passed to as.mask to control the pixel resolution.

When w is a window, the default (when polygonal=NULL) is to compute a polygonal approximation if w is a rectangle or polygonal window, and to compute a pixel approximation if w is a window of type "mask".

Examples

Run this code

  plot(dilation(redwood, 0.05))
  points(redwood)

  plot(dilation(letterR, 0.2))
  plot(letterR, add=TRUE, lwd=2, border="red")

  X <- psp(runif(10), runif(10), runif(10), runif(10), window=owin())
  plot(dilation(X, 0.1))
  plot(X, add=TRUE, col="red")

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