rpoint: Generate N Random Points

Description Usage Arguments Details Value Author(s) See Also Examples

View source: R/random.R

Description

Generate a random point pattern containing n independent, identically distributed random points with any specified distribution.

Usage

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 rpoint(n, f, fmax=NULL, win=unit.square(),
        ..., giveup=1000, verbose=FALSE,
        nsim=1, drop=TRUE)

Arguments

n

Number of points to generate.

f

The probability density of the points, possibly un-normalised. Either a constant, a function f(x,y,...), or a pixel image object.

fmax

An upper bound on the values of f. If missing, this number will be estimated.

win

Window in which to simulate the pattern. Ignored if f is a pixel image.

...

Arguments passed to the function f.

giveup

Number of attempts in the rejection method after which the algorithm should stop trying to generate new points.

verbose

Flag indicating whether to report details of performance of the simulation algorithm.

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.

Details

This function generates n independent, identically distributed random points with common probability density proportional to f.

The argument f may be

a numerical constant:

uniformly distributed random points will be generated.

a function:

random points will be generated in the window win with probability density proportional to f(x,y,...) where x and y are the cartesian coordinates. The function f must accept two vectors of coordinates x,y and return the corresponding vector of function values. Additional arguments ... of any kind may be passed to the function.

a pixel image:

if f is a pixel image object of class "im" (see im.object) then random points will be generated in the window of this pixel image, with probability density proportional to the pixel values of f.

The algorithm is as follows:

The algorithm for pixel images is more efficient than that for functions.

Value

A point pattern (an object of class "ppp") if nsim=1, or a list of point patterns if nsim > 1.

Author(s)

\adrian

and \rolf

See Also

ppp.object, owin.object, runifpoint

Examples

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 # 100 uniform random points in the unit square
 X <- rpoint(100)

 # 100 random points with probability density proportional to x^2 + y^2
 X <- rpoint(100, function(x,y) { x^2 + y^2}, 1)

 # `fmax' may be omitted
 X <- rpoint(100, function(x,y) { x^2 + y^2})

 # irregular window
 data(letterR)
 X <- rpoint(100, function(x,y) { x^2 + y^2}, win=letterR)

 # make a pixel image 
 Z <- setcov(letterR)
 # 100 points with density proportional to pixel values
 X <- rpoint(100, Z)

spatstat documentation built on Aug. 16, 2017, 5:07 p.m.