spatstat (version 1.23-1)

tess: Create a Tessellation

Description

Creates an object of class "tess" representing a tessellation of a spatial region.

Usage

tess(..., xgrid = NULL, ygrid = NULL, tiles = NULL, image = NULL,
            window=NULL, keepempty=FALSE)

Arguments

...

Ignored.

xgrid,ygrid

Cartesian coordinates of vertical and horizontal lines determining a grid of rectangles. Incompatible with other arguments.

tiles

List of tiles in the tessellation. A list, each of whose elements is a window (object of class "owin"). Incompatible with other arguments.

image

Pixel image which specifies the tessellation. Incompatible with other arguments.

window

Optional. The spatial region which is tessellated (i.e. the union of all the tiles). An object of class "owin".

keepempty

Logical flag indicating whether empty tiles should be retained or deleted.

Value

• An object of class "tess" representing the tessellation.

Details

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: [object Object],[object Object],[object Object]

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, or tile.areas to compute their areas.

Tessellations can be used to classify the points of a point pattern, in split.ppp, cut.ppp and by.ppp.

See Also

plot.tess, [.tess, as.tess, tiles, intersect.tess, split.ppp, cut.ppp, by.ppp, quadrats, bdist.tiles, tile.areas.

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