In the spatstat library, a point pattern dataset must include
information about the window or region in which the pattern was
observed. A window is described by an object of class "owin"
.
Windows of arbitrary shape are supported.
An object of class "owin"
has one of three types:
"rectangle" : 
a rectangle in the twodimensional plane with edges parallel to the axes

"polygonal" : 
a region whose boundary is a polygon or several polygons.
The region may have holes and may consist of several disconnected pieces.

Objects of class "owin"
may be created by the function
owin
and converted from other types of data by the function
as.owin
.
They may be manipulated by the functions
as.rectangle
,
as.mask
,
complement.owin
,
rotate
,
shift
,
affine
,
erosion
,
dilation
,
opening
and
closing
.
Geometrical calculations available for windows include
area.owin
,
perimeter
,
diameter.owin
,
boundingbox
,
eroded.areas
,
bdist.points
,
bdist.pixels
,
and
even.breaks.owin
.
The mapping between continuous coordinates and pixel raster indices
is facilitated by the functions
raster.x
,
raster.y
and
nearest.raster.point
.
There is a plot
method for window objects,
plot.owin
. This may be useful if you wish to
plot a point pattern's window without the points for graphical
purposes.
There are also methods for
summary
and print
.