R: Point Pair Orientation Distribution

pairorient {spatstat.core} | R Documentation

## 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, ..., cumulative=FALSE,
               correction, ratio = FALSE,
               unit=c("degree", "radian"), domain=NULL)

### Arguments

`X` | Point pattern (object of class `"ppp"`).
`r1,r2` | Minimum and maximum values of distance to be considered.
`...` | Arguments passed to `circdensity` to control the kernel smoothing, if `cumulative=FALSE`.
`cumulative` | Logical value specifying whether to estimate the probability density (`cumulative=FALSE`, the default) or the cumulative distribution function (`cumulative=TRUE`).
`correction` | Character vector specifying edge correction or corrections. Options are `"none"`, `"isotropic"`, `"translate"`, `"border"`, `"bord.modif"`, `"good"` and `"best"`. Alternatively `correction="all"` selects all options. The default is to compute all edge corrections except `"none"`.
`ratio` | Logical. If `TRUE`, the numerator and denominator of each edge-corrected estimate will also be saved, for use in analysing replicated point patterns.
`unit` | Unit in which the angles should be expressed. Either `"degree"` or `"radian"`.
`domain` | Optional window. The first point x[i] of each pair of points will be constrained to lie in `domain`.

### Details

This algorithm 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 or radians, anticlockwise from the x axis.

If `cumulative=FALSE` (the default), a kernel estimate of the probability density of the orientations is calculated using `circdensity`.

If `cumulative=TRUE`, then the cumulative distribution function of these directions is calculated. This is the function O[r1,r2](phi) defined in Stoyan and Stoyan (1994), equation (14.53), page 271.

In either case the result can be plotted as a rose diagram by `rose`, or as a function plot by `plot.fv`.

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`. See the help for `Kest` for details of edge corrections, and explanation of the options available. The choice `correction="none"` is not recommended; it is included for demonstration purposes only. The default is to compute all corrections except `"none"`.

It is also possible to calculate an estimate of the probability density from the cumulative distribution function, by numerical differentiation. Use `deriv.fv` with the argument `Dperiodic=TRUE`.

### Value

A function value table (object of class `"fv"`) containing the estimates of the probability density or the cumulative distribution function of angles, in degrees (if `unit="degree"`) or radians (if `unit="radian"`).

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner r.turner@auckland.ac.nz and Ege Rubak rubak@math.aau.dk.

### 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`, `nnorient`

### Examples

      rose(pairorient(redwood, 0.05, 0.15, sigma=8), col="grey")
      plot(CDF <- pairorient(redwood, 0.05, 0.15, cumulative=TRUE))
      plot(f <- deriv(CDF, spar=0.6, Dperiodic=TRUE))

[Package spatstat.core version 2.0-0 Index]