erode.owin: Erode a Window

Description

Perform morphological erosion of a window

Usage

erosion.owin(w, r, shrink.frame=TRUE, ..., strict=FALSE, polygonal=TRUE)
 erode.owin(w, r, shrink.frame=TRUE, ..., strict=FALSE, polygonal=TRUE)

Arguments

A window (object of class "owin".

positive number: the radius of erosion.

shrink.frame

logical: if TRUE, erode the bounding rectangle as well.

...

extra arguments to as.mask controlling the pixel resolution, if pixel approximation is used.

strict

Logical flag determining the fate of boundary pixels, if pixel approximation is used. See details.

polygonal

Logical flag indicating whether to compute a polygonal approximation to the erosion (polygonal=TRUE) or a pixel grid approximation (polygonal=FALSE).

Value

Another object of class "owin" representing the eroded window.

Details

The morphological erosion of a set $W$ by a distance $r > 0$ is the subset consisting of all points $x \in W$ such that the distance from $x$ to the boundary of $W$ is greater than or equal to $r$. In other words it is the result of trimming a margin of width $r$ off the set $W$.

The functions erode.owin and erosion.owin are identical; they compute the erosion of the window w.

If w is a rectangle, the result will be a rectangle, or empty.

If w is a polygonal window and polygonal=TRUE, a polygonal approximation to the eroded window will be computed.

Otherwise, w and its erosion will be approximated by a binary pixel image. The arguments "..." are passed to as.mask to determine the pixel resolution. There is a sensible default.

The erosion consists of all pixels whose distance from the boundary of w is strictly greater than r (if strict=TRUE) or is greater than or equal to r (if strict=FALSE). If shrink.frame is false, the resulting window is given the same outer, bounding rectangle as the original window w. If shrink.frame is true, the original bounding rectangle is also eroded by the same distance r.

To simply compute the area of the eroded window, use eroded.areas.

Examples

Run this code

w <- owin(c(0,1),c(0,1))
  v <- erode.owin(w, 0.1) 
  # returns rectangle [0.1, 0.9] x [0.1,0.9]
  v <- erode.owin(w, 0.6)
  # erosion is empty

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