spatstat (version 1.23-1)

nnwhich.pp3: Nearest neighbours in three dimensions

Description

Finds the nearest neighbour of each point in a three-dimensional point pattern.

Usage

## S3 method for class 'pp3':
nnwhich(X, \dots, k=1)

Arguments

X

Three-dimensional point pattern (object of class "pp3").

...

Ignored.

k

Integer, or integer vector. The algorithm will compute the distance to the kth nearest neighbour.

Value

• Numeric vector or matrix giving, for each point, the index of its nearest neighbour (or kth nearest neighbour).

  If k = 1 (the default), the return value is a numeric vector v giving the indices of the nearest neighbours (the nearest neighbout of the ith point is the jth point where j = v[i]). If k is a single integer, then the return value is a numeric vector giving the indices of the kth nearest neighbours.

  If k is a vector, then the return value is a matrix m such that m[i,j] is the index of the k[j]th nearest neighbour for the ith data point.

Warnings

A value of NA is returned if there is only one point in the point pattern.

Details

For each point in the given three-dimensional point pattern, this function finds its nearest neighbour (the nearest other point of the pattern). By default it returns a vector giving, for each point, the index of the point's nearest neighbour. If k is specified, the algorithm finds each point's kth nearest neighbour.

The function nnwhich is generic. This is the method for the class "pp3".

If there are no points in the pattern, a numeric vector of length zero is returned. If there is only one point, then the nearest neighbour is undefined, and a value of NA is returned. In general if the number of points is less than or equal to k, then a vector of NA's is returned.

To evaluate the distance between a point and its nearest neighbour, use nndist.

To find the nearest neighbours from one point pattern to another point pattern, use nncross.

See Also

nnwhich, nndist, nncross

Examples

X <- runifpoint3(30)
   m <- nnwhich(X)
   m2 <- nnwhich(X, k=2)