quadrats {spatstat.geom}

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)

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.

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.

Value

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

Author(s)

Adrian Baddeley [e-mail] and Rolf Turner [e-mail]

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))