as.mask | R Documentation |
Obtain a discrete (pixel image) approximation of a given window
as.mask(w, eps=NULL, dimyx=NULL, xy=NULL)
w |
A window (object of class |
eps |
(optional) width and height of pixels. |
dimyx |
(optional) pixel array dimensions |
xy |
(optional) data containing pixel coordinates |
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 * 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.
A window (object of class "owin"
)
of type "mask"
representing a binary pixel image.
and \rolf
owin.object
,
as.rectangle
,
as.polygonal
,
spatstat.options
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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