distmap.ppp {spatstat.geom}

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, ..., clip=FALSE, metric=NULL)

Arguments

X

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

...

Arguments passed to as.mask to control pixel resolution.

clip

Logical value specifying whether the resulting pixel image should be clipped to the window of X.

metric

Optional. A distance metric (object of class "metric", see metric.object) which will be used to compute the distances.

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.

If clip=FALSE (the default), the resulting pixel values are defined at every pixel in the rectangle Frame(X). If clip=TRUE, the pixel values are defined only inside Window(X), and are NA outside this window. Computation is faster when clip=FALSE.

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 boundary of the window containing X. 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.

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.

Author(s)

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

See Also

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

Generic function distfun.

Nearest neighbour distance nncross

Examples

  U <- distmap(cells)
  if(interactive()) {
    plot(U)
    plot(attr(U, "bdry"))
    plot(attr(U, "index"))
  }