Obtain a discrete (pixel image) approximation of a given window
as.mask(w, eps=NULL, dimyx=NULL, xy=NULL)A window (object of class "owin") or data acceptable
to as.owin.
(optional) width and height of pixels.
(optional) pixel array dimensions
(optional) data containing pixel coordinates
A window (object of class "owin")
of type "mask" representing a binary pixel image.
This function generates a rectangular grid of locations in the plane,
tests whether each of these locations lies inside the
window w, and stores the results as a binary pixel image
or `mask' (an object of class "owin", see owin.object).
The most common use of this function is to approximate the shape
of another window w by a binary pixel image. In this case,
we will usually want to have a very fine grid of pixels.
This function can also be used to generate a coarsely-spaced grid of locations inside a window, for purposes such as subsampling and prediction.
The grid spacing and location are controlled by the
arguments eps, dimyx and xy,
which are mutually incompatible.
If eps is given, then it determines the grid spacing.
If eps is a single number,
then the grid spacing will be approximately eps
in both the \(x\) and \(y\) directions. If eps is a
vector of length 2, then the grid spacing will be approximately
eps[1] in the \(x\) direction and
eps[2] in the \(y\) direction.
If dimyx is given, then the pixel grid will be an
\(m \times n\) rectangular grid
where \(m, n\) are given by dimyx[2], dimyx[1]
respectively. Warning: dimyx[1] is the number of
pixels in the \(y\) direction, and dimyx[2] is the number
in the \(x\) direction.
If xy is given, then this should be some kind of
data specifing the coordinates of a pixel grid. It may be
a list or structure containing elements x and y
which are numeric vectors of equal length. These will be taken as
\(x\) and y coordinates of the margins
of the grid. The pixel coordinates will be generated
from these two vectors.
a pixel image (object of class "im").
a window (object of class "owin") which is
of type "mask" so that it contains pixel coordinates.
If xy is given, w may be omitted.
If neither eps nor dimyx nor xy is given,
the pixel raster dimensions are obtained from
spatstat.options("npixel").
There is no inverse of this function. However, the function
as.polygonal will compute a polygonal approximation
of a binary mask.
# NOT RUN {
w <- owin(c(0,10),c(0,10), poly=list(x=c(1,2,3,2,1), y=c(2,3,4,6,7)))
m <- as.mask(w)
if(interactive()) {
plot(w)
plot(m)
}
x <- 1:9
y <- seq(0.25, 9.75, by=0.5)
m <- as.mask(w, xy=list(x=x, y=y))
# }
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