spatstat.geom (version 3.3-3)

quadrats: Divide Region into Quadrats

Description

Divides window into rectangular quadrats and returns the quadrats as a tessellation.

Usage

quadrats(X, nx = 5, ny = nx, xbreaks = NULL, ybreaks = NULL, keepempty=FALSE)

Value

A tessellation (object of class "tess") as described under

tess.

Arguments

X

A window (object of class "owin") or anything that can be coerced to a window using as.owin, such as a point pattern.

nx,ny

Numbers of quadrats in the \(x\) and \(y\) directions. Incompatible with xbreaks and ybreaks.

xbreaks

Numeric vector giving the \(x\) coordinates of the boundaries of the quadrats. Incompatible with nx.

ybreaks

Numeric vector giving the \(y\) coordinates of the boundaries of the quadrats. Incompatible with ny.

keepempty

Logical value indicating whether to delete or retain empty quadrats. See Details.

Author

Adrian Baddeley and Rolf Turner

Details

If the window X is a rectangle, it is divided into an nx * ny grid of rectangular tiles or `quadrats'.

If X is not a rectangle, then the bounding rectangle of X is first divided into an nx * ny grid of rectangular tiles, and these tiles are then intersected with the window X.

The resulting tiles are returned as a tessellation (object of class "tess") which can be plotted and used in other analyses.

If xbreaks is given, it should be a numeric vector giving the \(x\) coordinates of the quadrat boundaries. If it is not given, it defaults to a sequence of nx+1 values equally spaced over the range of \(x\) coordinates in the window Window(X).

Similarly if ybreaks is given, it should be a numeric vector giving the \(y\) coordinates of the quadrat boundaries. It defaults to a vector of ny+1 values equally spaced over the range of \(y\) coordinates in the window. The lengths of xbreaks and ybreaks may be different.

By default (if keepempty=FALSE), any rectangular tile which does not intersect the window X is ignored, and only the non-empty intersections are treated as quadrats, so the tessellation may consist of fewer than nx * ny tiles. If keepempty=TRUE, empty intersections are retained, and the tessellation always contains exactly nx * ny tiles, some of which may be empty.

See Also

For calculations using quadrats, see quadratcount, quadrat.test, quadratresample

For other kinds of tessellations, see tess, hextess, venn.tess, polartess, dirichlet, delaunay, quantess, bufftess and rpoislinetess.

Examples

 W <- square(10)
 Z <- quadrats(W, 4, 5)
 plot(Z)

 plot(quadrats(letterR, 5, 7))