spatstat.geom (version 3.3-2)

rexplode: Explode a Point Pattern by Displacing Duplicated Points

Description

Given a point pattern which contains duplicated points, separate the duplicated points from each other by slightly perturbing their positions.

Usage

rexplode(X, ...)
# S3 method for ppp
rexplode(X, radius, ..., nsim = 1, drop = TRUE)

Value

A point pattern (an object of class "ppp") or a list of point patterns.

Arguments

X

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

radius

Scale of perturbations. A positive numerical value. The displacement vectors will be uniformly distributed in a circle of this radius. There is a sensible default. Alternatively, radius may be a numeric vector of length equal to the number of points in X, giving a different displacement radius for each data point. Radii will be restricted to be less than or equal to the distance to the boundary of the window.

...

Ignored.

nsim

Number of simulated realisations to be generated.

drop

Logical. If nsim=1 and drop=TRUE (the default), the result will be a point pattern, rather than a list containing a point pattern.

Author

Adrian Baddeley .

Details

Duplicated points in the point pattern X are identified. Each group of duplicated points is then ‘exploded’ by randomly displacing the point locations to form a circular arrangement around the original position.

This function is an alternative to rjitter.ppp. Whereas rjitter.ppp applies independent random displacements to each data point, rexplode.ppp applies displacements only to the points that are duplicated, and the displacements are mutually dependent within each group of duplicates, to ensure that the displaced points are visually separated from each other.

First the code ensures that the displacement radius for each data point is less than or equal to the distance to the boundary of the window. Then each group of duplicated points (or data points with the same location but possibly different mark values) is taken in turn. The first element of the group is randomly displaced by a vector uniformly distributed in a circle of radius radius. The remaining elements of the group are then positioned around the original location, at the same distance from the orginal location, with equal angular spacing from the first point. The result is that each group of duplicated points becomes a circular pattern centred around the original location.

See Also

rjitter.ppp

Examples

   ## create a pattern containing duplicated points
   X <- runifrect(5) %mark% letters[1:5]
   X <- X[rep(1:5, 1 + rpois(5, 2))]
   ## explode it
   Y <- rexplode(X, 0.05)
   ## display
   if(interactive()) {
       plot(solist(X=X, 'explode(X)'=Y),
       main="", cols=2:6, cex=1.25, leg.side="bottom")
   }