owin {spatstat.geom} | R Documentation |
Create a Window
Description
Creates an object of class "owin"
representing
an observation window in the two-dimensional plane
Usage
owin(xrange=c(0,1), yrange=c(0,1), ..., poly=NULL, mask=NULL,
unitname=NULL, xy=NULL)
Arguments
xrange |
|
yrange |
|
... |
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 |
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
andyrange
are given, then the window will be rectangular, with itsx
andy
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 dimensionsxrange=c(0,1)
andyrange=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 vectorsx
andy
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 entrypoly[[i]]
of which is a matrix or data frame with two columns or a structure with two component vectorsx
andy
of equal length, then the successive list memberspoly[[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 thatmask[i,j]
isTRUE
if the point(x[j],y[i])
belongs to the window, andFALSE
if it does not (NA
entries will be treated asFALSE
). Note carefully that rows ofmask
correspond to they
coordinate, and columns to thex
coordinate. Herex
andy
are vectors ofx
andy
coordinates equally spaced overxrange
andyrange
respectively. The pixel coordinate vectorsx
andy
may be specified explicitly using the argumentxy
, which should be a list containing componentsx
andy
. 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.
-
To create a window which is mathematically
defined by inequalities in the Cartesian coordinates,
use raster.x()
and raster.y()
as in the examples below.
Functions square
and disc
will create square and circular windows, respectively.
Value
An object of class "owin"
describing a window in the two-dimensional plane.
Validity of polygon data
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)
.
Author(s)
Adrian Baddeley Adrian.Baddeley@curtin.edu.au
and Rolf Turner rolfturner@posteo.net
See Also
owin.object
,
as.owin
,
complement.owin
,
ppp.object
,
ppp
square
,
hexagon
,
regularpolygon
, disc
,
ellipse
.
Examples
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)