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)

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".

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. There are methods for print, plot, [ and [<- for tessellations. Use tiles to extract the list of tiles in a tessellation.

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

Examples

Run this code

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

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