| owin {spatstat} | R Documentation |
Creates an object of class "owin" representing
an observation window in the two-dimensional plane
owin(xrange=c(0,1), yrange=c(0,1), ..., poly=NULL, mask=NULL, units=NULL)
xrange |
x coordinate limits of enclosing box |
yrange |
y coordinate limits of enclosing box |
... |
Ignored. |
poly |
Optional. Polygonal boundary of window.
Incompatible with mask.
|
mask |
Optional. Logical matrix giving binary image of window.
Incompatible with poly.
|
units |
Optional. Name of unit of length. Either a single character string, or a vector of two character strings giving the singular and plural forms, respectively. |
In the spatstat library, a point pattern dataset must include
information about the window of observation. This is represented by
an object of class "owin".
See owin.object for an overview.
To create a window in its own right,
users would normally invoke owin,
although sometimes as.owin may be convenient.
A window may be rectangular, polygonal, or a mask (a binary image).
xrange and yrange are given, then
the window will be rectangular, with its x and y
coordinate dimensions given by these two arguments
(which must be vectors of length 2).
If no arguments are given at all, the default is the unit square
with dimensions xrange=c(0,1) and yrange=c(0,1).
poly is given, then the window will be polygonal.
poly is a structure with
two component vectors x and y of equal length,
then these vectors are interpreted as the cartesian coordinates
of the vertices of a polygon circumscribing the window.
The vertices must be listed anticlockwise.
No vertex should be repeated (i.e. do not repeat the first
vertex).
poly is a list, each entry poly[[i]]
of which is a structure with
two component vectors x and y of equal length,
then the successive list members poly[[i]]
are interpreted as separate polygons which together
make up the boundary of the window.
The vertices of each polygon must be listed anticlockwise
if the polygon is part of the external boundary,
but clockwise
if the polygon is the boundary of a hole in the window.
Again, do not repeat any vertex.
mask is given, then the window will be a binary image.
The argument mask should be a logical matrix
such that mask[i,j] is TRUE if the point
(x[j],y[i]) belongs to the window, and FALSE if it
does not. Note carefully that rows of mask correspond to the
y coordinate, and columns to the x coordinate.
Here x and y are vectors of x and y
coordinates equally spaced over xrange and yrange
respectively.
raster.x() and raster.y()
as in the examples below.
Functions square and disc
will create square and circular windows, respectively.
An object of class "owin"
describing a window in the two-dimensional plane.
Adrian Baddeley adrian@maths.uwa.edu.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner rolf@math.unb.ca http://www.math.unb.ca/~rolf
square,
disc,
owin.object,
as.owin,
complement.owin,
ppp.object,
ppp
w <- owin()
w <- owin(c(0,1), c(0,1))
# the unit square
w <- owin(c(10,20), c(10,30), units=c("foot","feet"))
# a rectangle of dimensions 10 x 20 feet
# with lower left corner at (10,10)
# polygon (diamond shape)
w <- owin(poly=list(x=c(0.5,1,0.5,0),y=c(0,1,2,1)))
w <- owin(c(0,1), c(0,2), poly=list(x=c(0.5,1,0.5,0),y=c(0,1,2,1)))
# polygon with hole
ho <- owin(poly=list(list(x=c(0,1,1,0), y=c(0,0,1,1)),
list(x=c(0.6,0.4,0.4,0.6), y=c(0.2,0.2,0.4,0.4))))
w <- owin(c(-1,1), c(-1,1), mask=matrix(TRUE, 100,100))
# 100 x 100 image, all TRUE
X <- raster.x(w)
Y <- raster.y(w)
wm <- owin(w$xrange, w$yrange, mask=(X^2 + Y^2 <= 1))
# discrete approximation to the unit disc
## Not run:
plot(c(0,1),c(0,1),type="n")
bdry <- locator()
# click the vertices of a polygon (anticlockwise)
## End(Not run)
w <- owin(poly=bdry)
## Not run: plot(w)
## Not run:
im <- as.logical(matrix(scan("myfile"), nrow=128, ncol=128))
# read in an arbitrary 128 x 128 digital image from text file
rim <- im[, 128:1]
# Assuming it was given in row-major order in the file
# i.e. scanning left-to-right in rows from top-to-bottom,
# the use of matrix() has effectively transposed rows & columns,
# so to convert it to our format just reverse the column order.
w <- owin(mask=rim)
plot(w)
# display it to check!
## End(Not run)