nnmark {spatstat.geom}

Mark of Nearest Neighbour

Description

Given a marked point pattern dataset X this function computes, for each desired location y, the mark attached to the nearest neighbour of y in X. The desired locations y can be either a pixel grid or the point pattern X itself.

Usage

nnmark(X, ..., k = 1, at=c("pixels", "points"))

Arguments

X

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

...

Arguments passed to as.mask to determine the pixel resolution.

k

Single integer. The kth nearest data point will be used.

at

String specifying whether to compute the values at a grid of pixel locations (at="pixels") or only at the points of X (at="points").

Details

Given a marked point pattern dataset X this function computes, for each desired location y, the mark attached to the point of X that is nearest to y. The desired locations y can be either a pixel grid or the point pattern X itself.

The argument X must be a marked point pattern (object of class "ppp", see ppp.object). The marks are allowed to be a vector or a data frame.

• If at="points", then for each point in X, the algorithm finds the nearest other point in X, and extracts the mark attached to it. The result is a vector or data frame containing the marks of the neighbours of each point.

• If at="pixels" (the default), then for each pixel in a rectangular grid, the algorithm finds the nearest point in X, and extracts the mark attached to it. The result is an image or a list of images containing the marks of the neighbours of each pixel. The pixel resolution is controlled by the arguments ... passed to as.mask.

If the argument k is given, then the k-th nearest neighbour will be used.

Value

If X has a single column of marks:

• If at="pixels" (the default), the result is a pixel image (object of class "im"). The value at each pixel is the mark attached to the nearest point of X.

• If at="points", the result is a vector or factor of length equal to the number of points in X. Entries are the mark values of the nearest neighbours of each point of X.

If X has a data frame of marks:

• If at="pixels" (the default), the result is a named list of pixel images (object of class "im"). There is one image for each column of marks. This list also belongs to the class "solist", for which there is a plot method.

• If at="points", the result is a data frame with one row for each point of X, Entries are the mark values of the nearest neighbours of each point of X.

Author(s)

Adrian Baddeley [e-mail]

Rolf Turner [e-mail]

and Ege Rubak [e-mail]

See Also

Smooth.ppp, marktable, nnwhich

Examples

  plot(nnmark(ants))
  v <- nnmark(ants, at="points")
  v[1:10]
  plot(nnmark(finpines))
  vf <- nnmark(finpines, at="points")
  vf[1:5,]