Creates an object of class "tess" representing a tessellation
of a spatial region.
tess(..., xgrid = NULL, ygrid = NULL, tiles = NULL, image = NULL,
window=NULL, marks=NULL, keepempty=FALSE, unitname=NULL, check=TRUE)An object of class "tess" representing the tessellation.
Ignored.
Cartesian coordinates of vertical and horizontal lines determining a grid of rectangles. Incompatible with other arguments.
List of tiles in the tessellation.
A list, each of whose elements is a window
(object of class "owin"). Incompatible with other arguments.
Pixel image
(object of class "im")
which specifies the tessellation.
Incompatible with other arguments.
Optional.
The spatial region which is tessellated (i.e. the union of all the tiles).
An object of class "owin".
Optional vector or data frame of marks associated with the tiles.
Logical flag indicating whether empty tiles should be retained or deleted.
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.
If this argument is missing or NULL,
information about the unitname will be
extracted from the other arguments.
If this argument is given, it overrides any other information
about the unitname.
Logical value indicating whether to check the validity of the
input data. It is strongly recommended to use the default
value check=TRUE.
Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner r.turner@auckland.ac.nz and Ege Rubak rubak@math.aau.dk.
A tessellation is a collection of disjoint spatial regions
(called tiles) that fit together to form a larger spatial
region. This command creates an object of class "tess" that
represents a tessellation.
Three types of tessellation are supported:
tiles are rectangles, with sides parallel to the x and
y axes. They may or may not have equal size and shape.
The arguments xgrid and ygrid determine
the positions of the vertical and horizontal grid lines,
respectively. (See quadrats for another way to do this.)
tiles are arbitrary spatial regions.
The argument tiles is a list of these tiles,
which are objects of class "owin".
Tiles are subsets of a fine grid of pixels.
The argument image is a pixel image (object of class
"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 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 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.
Empty tiles may occur, either because one of the entries in the list
tiles is an empty window, or because one of the levels of the
factor-valued pixel image image does not occur in the pixel data.
When keepempty=TRUE, empty tiles are permitted.
When keepempty=FALSE (the default), tiles are not allowed to be
empty, and any empty tiles will be removed from the tessellation.
There are methods for print, plot, [ and [<-
for tessellations. Use tiles to extract the list of
tiles in a tessellation, tilenames to extract the names
of the tiles, and tile.areas to compute their
areas.
The tiles may have marks, which can be extracted by
marks.tess and changed by marks<-.tess.
Tessellations can be used to classify the points of
a point pattern, in split.ppp, cut.ppp and
by.ppp.
To construct particular tessellations, see
quadrats, hextess,
dirichlet, delaunay,
venn.tess,
polartess,
quantess,
bufftess
and rpoislinetess.
marks.tess,
plot.tess,
[.tess,
as.tess,
tiles,
intersect.tess,
split.ppp,
cut.ppp,
by.ppp,
bdist.tiles,
tile.areas,
as.function.tess.
To construct particular tessellations, see
quadrats, hextess,
venn.tess,
polartess,
dirichlet, delaunay, quantess
and rpoislinetess.
To divide space into pieces containing equal
amounts of stuff, use quantess.
To convert a tessellation to a function, for use as a spatial covariate
(associating a numerical value with each tile of the tessellation) use
as.function.tess.
A <- tess(xgrid=0:4,ygrid=0:4)
A
plot(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)
plot(E)
G <- tess(image=v, marks=toupper(levels(v)), unitname="km")
G
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