spatstat (version 1.15-3)

erode.owin: Erode a Window

Description

Perform morphological erosion of a window

Usage

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

Arguments

w

A window (object of class "owin".

r

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

strict

Logical flag determining the fate of boundary pixels. See details.

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 not a rectangle, it must be approximated by a binary pixel image, and the arguments "..." are passed to as.mask to determine the pixel resolution. There is a sensible default.

For non-rectangular windows, 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.

See Also

dilate.owin for the opposite operation. owin, as.owin, eroded.areas

Examples

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