spatstat (version 1.23-1)

distmap.ppp: Distance Map of Point Pattern

Description

Computes the distance from each pixel to the nearest point in the given point pattern.

Usage

## S3 method for class 'ppp':
distmap(X, \dots)

Arguments

X

A point pattern (object of class "ppp").

...

Arguments passed to as.mask to control pixel resolution.

Value

• A pixel image (object of class "im") whose greyscale values are the values of the distance map. The return value has attributes "index" and "bdry" which are also pixel images.

Details

The ``distance map'' of a point pattern $X$ is the function $f$ whose value f(u) is defined for any two-dimensional location $u$ as the shortest distance from $u$ to $X$.

This function computes the distance map of the point pattern X and returns the distance map as a pixel image. The greyscale value at a pixel $u$ equals the distance from $u$ to the nearest point of the pattern X.

Additionally, the return value has two attributes, "index" and "bdry", which are also pixel images. The grey values in "bdry" give the distance from each pixel to the bounding rectangle of the image. The grey values in "index" are integers identifying which point of X is closest. This is a method for the generic function distmap. Note that this function gives the distance from the centre of each pixel to the nearest data point. To compute the exact distance from a given spatial location to the nearest data point in X, use distfun or nncross.

See Also

Generic function distmap and other methods distmap.psp, distmap.owin. Generic function distfun.

Nearest neighbour distance nncross

Examples

data(cells)
  U <- distmap(cells)
  plot(U)
  plot(attr(U, "bdry"))
  plot(attr(U, "index"))