directlabels - utility.function - Positioning Method - chull.points

Calculate the points on the convex hull.

chull.points <- function(d,...){
  bpts <- d[with(d,chull(x,y)),]
  r <- data.frame(i1=1:nrow(bpts),i2=c(2:nrow(bpts),1))
  r$x1 <- bpts$x[r$i1]
  r$y1 <- bpts$y[r$i1]
  r$x2 <- bpts$x[r$i2]
  r$y2 <- bpts$y[r$i2]
  r
}