Morphological Erosion by a Disc
Perform morphological erosion of a window, a line segment pattern or a point pattern by a disc.
erosion(w, r, ...) ## S3 method for class 'owin' erosion(w, r, shrink.frame=TRUE, ..., strict=FALSE, polygonal=NULL) ## S3 method for class 'ppp' erosion(w, r,...) ## S3 method for class 'psp' erosion(w, r,...)
w |
A window (object of class |
r |
positive number: the radius of erosion. |
shrink.frame |
logical: if |
... |
extra arguments to |
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 ( |
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.
If polygonal=TRUE then a polygonal approximation
to the erosion is computed.
If polygonal=FALSE then a pixel approximation
to the erosion is computed from the distance map of w.
The arguments "\dots" are passed to as.mask
to control the pixel resolution.
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).
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".
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.
If r > 0, an object of class "owin" representing the
eroded region (or NULL if this region is empty).
If r=0, the result is identical to w.
Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner r.turner@auckland.ac.nz and Ege Rubak rubak@math.aau.dk
dilation for the opposite operation.
erosionAny for morphological erosion using any shape.
plot(letterR, main="erosion(letterR, 0.2)") plot(erosion(letterR, 0.2), add=TRUE, col="red")
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