Create a Window
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, unitname=NULL, xy=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 |
Optional. Logical matrix giving binary image of window.
Incompatible with |
unitname |
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. |
xy |
Optional. List with components |
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).
rectangular windows:
If only 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).
polygonal windows:
If poly is given, then the window will be polygonal.
single polygon:
If poly is a matrix or data frame with two columns, or
a structure with two component vectors x and y
of equal length,
then these values 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).
multiple polygons or holes:
If poly is a list, each entry poly[[i]]
of which is a matrix or data frame with two columns
or 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.
binary masks:
If mask is given, then the window will be a binary image.
Specified by logical matrix:
Normally 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. The pixel coordinate vectors x and y
may be specified explicitly using the argument xy, which
should be a list containing components x and y.
Alternatively there is a sensible default.
Specified by list of pixel coordinates:
Alternatively the argument mask can be a data frame
with 2 or 3 columns. If it has 2 columns, it is expected to
contain the spatial coordinates of all the
pixels which are inside the window.
If it has 3 columns,
it should contain the spatial coordinates (x,y)
of every pixel in the grid, and the logical value associated
with each pixel. The pixels may be listed in any order.
An object of class "owin"
describing a window in the two-dimensional plane.
Polygon data may contain geometrical inconsistencies such as
self-intersections and overlaps. These inconsistencies must be
removed to prevent problems in other spatstat functions.
By default, polygon data will be repaired automatically
using polygon-clipping code.
The repair process may change the number of vertices in a polygon
and the number of polygon components.
To disable the repair process, set spatstat.options(fixpolygons=FALSE).
Adrian Baddeley Adrian.Baddeley@curtin.edu.au
and Rolf Turner r.turner@auckland.ac.nz
w <- owin()
w <- owin(c(0,1), c(0,1))
# the unit square
w <- owin(c(10,20), c(10,30), unitname=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
# vertices of a polygon (listed anticlockwise)
bdry <- list(x=c(0.1,0.3,0.7,0.4,0.2),
y=c(0.1,0.1,0.5,0.7,0.3))
# vertices could alternatively be read from a file, or use locator()
w <- owin(poly=bdry)
## Not run:
# how to read in a binary mask from a file
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)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.