rassoc.matern {pcds}

Generation of points associated (in a Matern-like fashion) to a given set of points

Description

An object of class "Patterns". Generates n 2D points uniformly in \cup B(y_i,e) where Y_p=(y_1,y_2,\ldots,y_{n_y}) with n_y being number of Yp points for various values of e under the association pattern and B(y_i,e) is the ball centered at y_i with radius e.

The pattern resembles the Matern cluster pattern (see rMatClust in the spatstat.random package for further information (Baddeley and Turner (2005)). rMatClust(kappa, scale, mu, win) in the simplest case generates a uniform Poisson point process of "parent" points with intensity kappa. Then each parent point is replaced by a random cluster of "offspring" points, the number of points per cluster being Poisson(mu) distributed, and their positions being placed and uniformly inside a disc of radius scale centered on the parent point. The resulting point pattern is a realization of the classical "stationary Matern cluster process" generated inside the window win.

The main difference of rassoc.matern and rMatClust is that the parent points are Yp points which are given beforehand and we do not discard them in the end in rassoc.matern and the offspring points are the points associated with the reference points, Yp; e must be positive and very large values of e provide patterns close to CSR.

This function is also very similar to rassoc.circular, where rassoc.circular needs the study window to be specified, while rassoc.matern does not.

Usage

rassoc.matern(n, Yp, e)

Arguments

n

A positive integer representing the number of points to be generated.

Yp

A set of 2D points representing the reference points. The generated points are associated (in a Matern-cluster like fashion) with these points.

e

A positive real number representing the radius of the balls centered at Yp points. Only these balls are allowed for the generated points (i.e., generated points would be in the union of these balls).

Value

A list with the elements

type

The type of the point pattern

mtitle

The "main" title for the plot of the point pattern

parameters

Radial (i.e., circular) attraction parameter of the association pattern.

ref.points

The input set of attraction points Yp, i.e., points with which generated points are associated.

gen.points

The output set of generated points associated with Yp points.

tri.Yp

Logical output for triangulation based on Yp points should be implemented or not. if TRUE triangulation based on Yp points is to be implemented (default is set to FALSE).

desc.pat

Description of the point pattern

num.points

The vector of two numbers, which are the number of generated points and the number of attraction (i.e., Yp) points.

xlimit, ylimit

The possible ranges of the x- and y-coordinates of the generated points.

Author(s)

Elvan Ceyhan

References

Baddeley AJ, Turner R (2005). “spatstat: An R Package for Analyzing Spatial Point Patterns.” Journal of Statistical Software, 12(6), 1-42.

See Also

rassoc.circular, rassoc.std.tri, rassocII.std.tri, rassoc.multi.tri, rseg.circular, and rMatClust in the spatstat.random package

Examples

nx<-100; ny<-4;  #try also nx<-1000; ny<-10;

e<-.15;
 #try also e<-1.1; #closer to CSR than association, as e is large

#Y points uniform in unit square
Y<-cbind(runif(ny),runif(ny))

Xdt<-rassoc.matern(nx,Y,e)
Xdt
summary(Xdt)
plot(Xdt,asp=1)

Xdt<-Xdt$gen.points
Xlim<-range(Xdt[,1],Y[,1]);
Ylim<-range(Xdt[,2],Y[,2])
xd<-Xlim[2]-Xlim[1]
yd<-Ylim[2]-Ylim[1]

plot(Y,asp=1,xlab="x",ylab="y",
main="Matern-like Association of X points with Y Points",
     xlim=Xlim+xd*c(-.01,.01),ylim=Ylim+yd*c(-.01,.01),
     pch=16,col=2,lwd=2)
points(Xdt)

a1<-0; a2<-10;
b1<-0; b2<-5;
e<-1.1;

#Y points uniform in a rectangle
Y<-cbind(runif(ny,a1,a2),runif(ny,b1,b2))
#try also Y<-cbind(runif(ny,a1,a2/2),runif(ny,b1,b2/2))

Xdt<-rassoc.matern(nx,Y,e)$gen.points
Xlim<-range(Xdt[,1],Y[,1]);
Ylim<-range(Xdt[,2],Y[,2])
xd<-Xlim[2]-Xlim[1]
yd<-Ylim[2]-Ylim[1]

plot(Y,asp=1,xlab="x",ylab="y",
main="Matern-like Association of X points with Y Points",
     xlim=Xlim+xd*c(-.01,.01),ylim=Ylim+yd*c(-.01,.01),pch=16,col=2,lwd=2)
points(Xdt)