owin to define the ``observation window'' of a point pattern
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
Windows of arbitrary shape are supported.
An object of class
"owin" has one of three types:
"rectangle": a rectangle in the two-dimensional 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.
"mask": a binary image (a logical matrix)
TRUE for pixels inside the window and
FALSE outside the window.
Objects of class
"owin" may be created by the function
and converted from other types of data by the function
Geometrical calculations available for windows include
The mapping between continuous coordinates and pixel raster indices
is facilitated by the functions
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
There are also methods for
In a window of type
row index corresponds to increasing $y$ coordinate,
and the column index corresponds to increasing $x$ coordinate.
w <- owin() w <- owin(c(0,1), c(0,1)) # the unit square w <- owin(c(0,1), c(0,2)) plot(w) # plots edges of a box 1 unit x 2 units v <- locator() # click on points in the plot window # to be the vertices of a polygon # traversed in anticlockwise order u <- owin(c(0,1), c(0,2), poly=v) plot(u) # plots polygonal boundary using polygon() plot(as.mask(u, eps=0.02)) # plots discrete pixel approximation to polygon