random - R generate points with condition using runifpoint function

Question

I am trying to generate randomly distributed points in a rectangle.

To create 50 random points in a rectangle, I used

i=50
  pp<-runifpoint(i, win=owin(c(0,19.5),c(0,3.12))

If I were to add conditions on the coordinates before randomly generating points,

e.g. 0.24 <x<19.26 ,0.24<y<2.64 , then generate random points, what code can I imply?

The ultimate goal is to generate points in the rectangle except for the grey shaded area, in the below image

Answer 1

This is a question about the R package spatstat.

The argument win specifies the spatial region in which the points will be generated. In your example you have specified this region to be a rectangle. You just need to replace this rectangle by the region in which you want the points to be generated.

You can construct spatial regions (objects of class owin) in many ways. See help(owin), or help(spatstat) for an overview.

In your example, you could build up the shape by forming the union of several rectangles. For example to make a simple cross shape, I could just write

require(spatstat)
A <- owin(c(-1,1), c(-4, 4))
B <- owin(c(-4,4), c(-1,1))
U <- union.owin(A, B)
plot(U)

Another way would be to specify the corners of the polygon shape and use W <- owin(poly=p) where p = list(x, y) contains the coordinates of the corners, listed in anticlockwise order without repetition. See help(owin).

This is also covered in Section 3.5 of the spatstat book. You can download Chapter 3 for free.