spatstat (version 1.31-3)

nnfun: Nearest Neighbour Map as a Function

Description

Compute the nearest neighbour map of an object, and return it as a function.

Usage

nnfun(X, ...)
  ## S3 method for class 'ppp':
nnfun(X, ...)
  ## S3 method for class 'psp':
nnfun(X, ...)

Arguments

X

Any suitable dataset representing a two-dimensional collection of objects, such as a point pattern (object of class "ppp") or a line segment pattern (object of class "psp").

...

Extra arguments are ignored.

Value

• A function with arguments x,y. The function also belongs to the class "nnfun" which has a method for print. It also belongs to the class "funxy" which has methods for plot, contour and persp.

Details

For a collection $X$ of two dimensional objects (such as a point pattern or a line segment pattern), the nearest neighbour function of $X$ is the mathematical function $f$ such that, for any two-dimensional spatial location $(x,y)$, the function value f(x,y) is the index $i$ identifying the closest member of $X$. That is, if $i = f(x,y)$ then $X[i]$ is the closest member of the collection $X$ to the location $(x,y)$. The command f <- nnfun(X) returns a function in the Rlanguage, with arguments x,y, that represents the nearest neighbour function of X. Evaluating the function f in the form v <- f(x,y), where x and y are any numeric vectors of equal length containing coordinates of spatial locations, yields the values of the distance function at these locations.

The result of f <- nnfun(X) also belongs to the class "funxy" and to the special class "nnfun". It can be printed and plotted immediately as shown in the Examples. A nnfun object can be converted to a pixel image using as.im.

See Also

distfun, plot.funxy

Examples

f <- nnfun(cells)
   f
   plot(f)
   f(0.2, 0.3)