spatstat (version 1.38-0)

pairorient: Point Pair Orientation Distribution

Description

Computes the distribution of the orientation of vectors joining pairs of points at a particular range of distances.

Usage

pairorient(X, r1, r2, ..., correction, ratio = FALSE)

Arguments

X

Point pattern (object of class "ppp").

r1,r2

Minimum and maximum values of distance to be considered.

...

Ignored.

correction

Character vector specifying edge correction or corrections. Options are "none", "isotropic", "translate", "good" and "best".

ratio

Logical. If TRUE, the numerator and denominator of each edge-corrected estimate will also be saved, for use in analysing replicated point patterns.

Value

• A function value table (object of class "fv") containing the estimates of the cumulative distribution function of angles, in degrees.

Details

This function calculates the point pair orientation distribution function $O_{r1,r2}(\phi)$ defined in Stoyan and Stoyan (1994), equation (14.53), page 271.

The function considers all pairs of points in the pattern X that lie more than r1 and less than r2 units apart. The direction of the arrow joining the points is measured, as an angle in degrees, anticlockwise from the $x$ axis. The result is the cumulative distribution function of these directions.

In calculating the cumulative distribution function, the algorithm gives each observed direction a weight, determined by an edge correction, to adjust for the fact that some interpoint distances are more likely to be observed than others. The choice of edge correction or corrections is determined by the argument correction.

To calculate the probability density of directions, use deriv.fv with the argument Dperiodic=TRUE.

References

Stoyan, D. and Stoyan, H. (1994) Fractals, random shapes and point fields: methods of geometrical statistics. John Wiley and Sons.

See Also

Kest, Ksector

Examples

plot(f <- pairorient(redwood, 0.05, 0.15))
  plot(Df <- deriv(f, spar=0.6, Dperiodic=TRUE))