https://github.com/cran/spatstat
Tip revision: 198d8db539783cb2d4f1347b81b82519926116b2 authored by Adrian Baddeley on 01 April 2009, 11:43:18 UTC
version 1.15-1
version 1.15-1
Tip revision: 198d8db
tess.Rd
\name{tess}
\alias{tess}
\title{Create a Tessellation}
\description{
Creates an object of class \code{"tess"} representing a tessellation
of a spatial region.
}
\usage{
tess(..., xgrid = NULL, ygrid = NULL, tiles = NULL, image = NULL,
window=NULL)
}
\arguments{
\item{\dots}{Ignored.}
\item{xgrid,ygrid}{Cartesian coordinates of vertical and
horizontal lines determining a grid of rectangles.
Incompatible with other arguments.
}
\item{tiles}{List of tiles in the tessellation.
A list, each of whose elements is a window
(object of class \code{"owin"}). Incompatible with other arguments.
}
\item{image}{
Pixel image which specifies the tessellation.
Incompatible with other arguments.
}
\item{window}{
Optional.
The spatial region which is tessellated (i.e. the union of all the tiles).
An object of class \code{"owin"}.
}
}
\details{
A tessellation is a collection of disjoint spatial regions
(called \emph{tiles}) that fit together to form a larger spatial
region. This command creates an object of class \code{"tess"} that
represents a tessellation.
Three types of tessellation are supported:
\describe{
\item{rectangular:}{
tiles are rectangles, with sides parallel to the \code{x} and
\code{y} axes. They may or may not have equal size and shape.
The arguments \code{xgrid} and \code{ygrid} determine
the positions of the vertical and horizontal grid lines,
respectively. (See \code{\link{quadrats}} for another way to do this.)
}
\item{tile list:}{
tiles are arbitrary spatial regions.
The argument \code{tiles} is a list of these tiles,
which are objects of class \code{"owin"}.
}
\item{pixel image:}{
Tiles are subsets of a fine grid of pixels.
The argument \code{image} is a pixel image (object of class
\code{"im"}) with factor values. Each level of the factor
represents a different tile of the tessellation. The pixels that
have a particular value of the factor constitute a tile.
}
}
The optional argument \code{window} specifies the spatial region
formed by the union of all the tiles. In other words it specifies the
spatial region that is divided into tiles by the tessellation.
If this argument is missing or \code{NULL}, it will be determined by
computing the set union of all the tiles. This is a time-consuming
computation. For efficiency it is advisable to specify the window.
Note that the validity of the window will not be checked.
There are methods for \code{print}, \code{plot}, \code{[} and \code{[<-}
for tessellations. Use \code{\link{tiles}} to extract the list of
tiles in a tessellation.
Tessellations can be used to classify the points of
a point pattern, in \code{\link{split.ppp}}, \code{\link{cut.ppp}} and
\code{\link{by.ppp}}.
}
\value{
An object of class \code{"tess"} representing the tessellation.
}
\seealso{
\code{\link{plot.tess}},
\code{\link{[.tess}},
\code{\link{as.tess}},
\code{\link{tiles}},
\code{\link{intersect.tess}},
\code{\link{split.ppp}},
\code{\link{cut.ppp}},
\code{\link{by.ppp}},
\code{\link{quadrats}}.
}
\examples{
A <- tess(xgrid=0:4,ygrid=0:4)
A
B <- A[c(1, 2, 5, 7, 9)]
B
v <- as.im(function(x,y){factor(round(5 * (x^2 + y^2)))}, W=owin())
levels(v) <- letters[seq(length(levels(v)))]
E <- tess(image=v)
E
}
\author{Adrian Baddeley
\email{adrian@maths.uwa.edu.au}
\url{http://www.maths.uwa.edu.au/~adrian/}
and Rolf Turner
\email{r.turner@auckland.ac.nz}
}
\keyword{spatial}
\keyword{datagen}