swin: Creating a sampling window

Description

Function swin creates an object of class "swin", which represents the sampling window (or study region) in which a spatial point pattern was observed. The ads library supports simple (rectangular or circular) and complex sampling windows.

Usage

swin(window, triangles)

Arguments

window

a vector defining the limits of a simple sampling window: c(xmin,ymin,xmax,ymax) for a rectangle ; c(x0,y0,r0) for a circle.

triangles

(optional) a list of triangles removed from a simple initial window to define a complex sampling window (see Details).

Value

An object of class "swin" describing the sampling window. It may be of four different types with different arguments:
$typea vector of two character strings defining the type of sampling window among c("simple","rectangle"), c("simple","circle"), c("complex","rectangle") or c("complex","circle").
$xmin,$ymin,$xmax,$ymax(optional) coordinates of the origin and the opposite corner for a rectangular sampling window (see details).
$x0,$y0,$r0(optional) coordinates of the center and radius for a circular sampling window (see details).
$triangles(optional) vertices coordinates of triangles for a complex sampling window (see details).

encoding

latin1

Details

A sampling window may be of simple or complex type. A simple sampling window may be a rectangle or a circle. A complex sampling window is defined by removing triangular surfaces from a simple (rectangular or circular) initial sampling window.

rectangular window:window=c(ximn,ymin,xmax,ymax)a vector of length 4 giving the coordinates$(ximn,ymin)$and$(xmax,ymax)$of the origin and the opposite corner of a rectangle.
circular window:window=c(x0,y0,r0)a vector of length 3 giving the coordinates$(x0,y0)$of the centre and the radius$r0$of a circle.
complex window:trianglesis a list of 6 variables giving the vertices coordinates $(ax,ay,bx,by,cx,cy)$of the triangles to remove from a simple (rectangular or circular) initial window. The triangles may be removed near the boundary of a rectangular window in order to design a polygonal sampling window, or within a rectangle or a circle, to delineating holes in the initial sampling window (see Examples). The triangles do not overlap each other, nor overlap boundary of the initial sampling window. Any polygon (possibly with holes) can be decomposed into contiguous triangles usingtriangulate.

References

Goreaud, F. and P�lissier, R. 1999. On explicit formula of edge effect correction for Ripley's K-function. Journal of Vegetation Science, 10:433-438.

Examples

Run this code

#rectangle of size [0,110] x [0,90]
  wr <- swin(c(0,0,110,90))
  summary(wr)
  plot(wr)
  
  #circle with radius 50 centred on (55,45)
  wc <- swin(c(55,45,50))
  summary(wc)
  plot(wc)
  
 # polygon (diamond shape)
 t1 <- c(0,0,55,0,0,45)
 t2 <- c(55,0,110,0,110,45)
 t3 <- c(0,45,0,90,55,90)
 t4 <- c(55,90,110,90,110,45)
 wp <- swin(wr, rbind(t1,t2,t3,t4))
 summary(wp)
 plot(wp)
 
 #rectangle with a hole
 h1 <- c(25,45,55,75,85,45)
 h2 <- c(25,45,55,15,85,45)
 wrh <- swin(wr, rbind(h1,h2))
 summary(wrh)
 plot(wrh)

 #circle with a hole
 wch <- swin(wc, rbind(h1,h2))
 summary(wch)
 plot(wch)
 
 #converting an owin object from spatstat
 data(demopat)
 demo.swin<-owin2swin(demopat$window)
 plot(demo.swin)

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