| bdist.pixels {spatstat.geom} | R Documentation |
Distance to Boundary of Window
Description
Computes the distances from each pixel in a window to the boundary of the window.
Usage
bdist.pixels(w, ..., style=c("image", "matrix", "coords"), method=c("C", "interpreted"))
Arguments
w |
A window (object of class |
... |
Arguments passed to |
style |
Character string (partially matched) determining the format of
the output: either |
method |
Choice of algorithm to use when |
Details
This function computes, for each pixel u in the
Frame containing the window w, the shortest distance
d(u, w^c) from u to the complement of
w. This value is zero for pixels lying outside w,
and is positive for pixels inside w.
If the window is a binary mask then the distance from each pixel
to the boundary is computed using the distance transform algorithm
distmap.owin. The result is equivalent to
distmap(W, invert=TRUE).
If the window is a rectangle or a polygonal region,
the grid of pixels is determined by the arguments "\dots"
passed to as.mask. The distance from each pixel to the
boundary is calculated exactly, using analytic geometry.
This is slower but more accurate than in the case of a binary mask.
For software testing purposes, there are two implementations
available when w is a polygon: the default is method="C"
which is much faster than method="interpreted".
To compute the distance from each pixel to the bounding rectangular frame
Frame(W), use framedist.pixels.
Value
If style="image", a pixel image (object of class "im")
containing the distances from each pixel in the image raster
to the boundary of the window.
If style="matrix",
a matrix giving the distances.
Rows of this matrix correspond to
the y coordinate and columns to the x coordinate.
If style="coords", a list with three components
x,y,z, where x,y are vectors of length m,n
giving the x and y coordinates respectively,
and z is an m \times n matrix such that
z[i,j] is the distance from (x[i],y[j]) to the
boundary of the window. Rows of this matrix correspond to the
x coordinate and columns to the y coordinate.
This result can be plotted with persp, image
or contour.
Author(s)
Adrian Baddeley Adrian.Baddeley@curtin.edu.au and Rolf Turner rolfturner@posteo.net
See Also
owin.object,
erosion,
bdist.points,
bdist.tiles,
distmap.owin.
Examples
u <- owin(c(0,1),c(0,1))
d <- bdist.pixels(u, eps=0.01)
image(d)
d <- bdist.pixels(u, eps=0.01, style="matrix")
mean(d >= 0.1)
# value is approx (1 - 2 * 0.1)^2 = 0.64
opa <- par(mfrow=c(1,2))
plot(bdist.pixels(letterR))
plot(framedist.pixels(letterR))
par(opa)