# owin

From spatstat v1.6-5
by Adrian Baddeley

##### Create a Window

Creates an object of class `"owin"`

representing
an observation window in the two-dimensional plane

- Keywords
- spatial

##### Usage

```
owin()
owin(xrange, yrange)
owin(poly=xy)
owin(xrange, yrange, poly=xy)
owin(xrange, yrange, mask=mat)
owin(mask=mat)
```

##### Arguments

- xrange
- $x$ coordinate limits of enclosing box
- yrange
- $y$ coordinate limits of enclosing box
- poly
- polygonal boundary of window
- mask
- logical matrix giving binary image of window

##### Details

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 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).*multiple polygons or holes:*If`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.

**binary masks:**If`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.
##### Value

- An object of class
`"owin"`

describing a window in the two-dimensional plane.

##### synopsis

owin(xrange=c(0,1), yrange=c(0,1), poly=NULL, mask=NULL)

##### See Also

##### Examples

```
w <- owin()
w <- owin(c(0,1), c(0,1))
# the unit square
w <- owin(c(10,20), c(10,30))
# a rectangle of dimensions 10 x 20 units
# with lower left corner at (10,10)
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)))
# diamond shape
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
plot(c(0,1),c(0,1),type="n")
bdry <- locator()
# click the vertices of a polygon (anticlockwise)
<testonly>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))</testonly>
w <- owin(poly=bdry)
plot(w)
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!
```

*Documentation reproduced from package spatstat, version 1.6-5, License: GPL version 2 or newer*

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