Perform morphological erosion of a window, a line segment pattern or a point pattern.
erosion(w, r, ...) ## S3 method for class 'owin': erosion(w, r, shrink.frame=TRUE, \dots, strict=FALSE, polygonal=NULL) ## S3 method for class 'ppp': erosion(w, r,\dots) ## S3 method for class 'psp': erosion(w, r,\dots)
- A window (object of class
"owin"or a line segment pattern (object of class
"psp") or a point pattern (object of class
- positive number: the radius of erosion.
- logical: if
TRUE, erode the bounding rectangle as well.
- extra arguments to
as.maskcontrolling the pixel resolution, if pixel approximation is used.
- Logical flag determining the fate of boundary pixels, if pixel approximation is used. See details.
- Logical flag indicating whether to compute a polygonal
approximation to the erosion (
polygonal=TRUE) or a pixel grid approximation (
polygonal=FALSE). Ignored if
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 $W$.
polygonal=TRUE then a polygonal approximation
to the erosion is computed.
polygonal=FALSE then a pixel approximation
to the erosion is computed from the distance map of
"..." are passed to
to control the pixel resolution.
The erosion consists of all pixels whose distance
from the boundary of
w is strictly greater than
strict=TRUE) or is greater than or equal to
w is a window, the default (when
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
Polygonal calculations require the
package which is subject to licence restrictions.
It is enabled by
shrink.frame is false, the resulting window is given the
same outer, bounding rectangle as the original window
shrink.frame is true, the original bounding rectangle
is also eroded by the same distance
To simply compute the area of the eroded window,
r > 0, an object of class
"owin"representing the eroded region (or
NULLif this region is empty). If
r=0, the result is identical to
w <- owin(c(0,1),c(0,1)) v <- erosion(w, 0.1) # returns rectangle [0.1, 0.9] x [0.1,0.9] v <- erosion(w, 0.6) # erosion is empty