sys3D <- function() {
    
  j <- c()
  k <- c()
  l <- c()

  xx3D <- c()
  yy3D <- c()

  g <- 1
  phi <- 30

  j <- c(j,+g); k <- c(k,+g); l <- c(l,-g/2)
  j <- c(j,-g); k <- c(k,+g); l <- c(l,-g/2)
  j <- c(j,-g); k <- c(k,-g); l <- c(l,-g/2)
  j <- c(j,+g); k <- c(k,-g); l <- c(l,-g/2)

  j <- c(j,+g); k <- c(k,+g); l <- c(l,+g/2)
  j <- c(j,-g); k <- c(k,+g); l <- c(l,+g/2)
  j <- c(j,-g); k <- c(k,-g); l <- c(l,+g/2)
  j <- c(j,+g); k <- c(k,-g); l <- c(l,+g/2)

  for (i in 1:8) {
     xx3D <- c(xx3D,j[i]-l[i]*cos(phi*pi/180))
     yy3D <- c(yy3D,k[i]-l[i]*sin(phi*pi/180))
  }

  plot(xx3D,yy3D)

  segments(x0=xx3D[1], y0=yy3D[1], x1=xx3D[2], y1=yy3D[2], col="red", lwd=2)
  segments(x0=xx3D[2], y0=yy3D[2], x1=xx3D[3], y1=yy3D[3], col="red", lwd=2)
  segments(x0=xx3D[3], y0=yy3D[3], x1=xx3D[4], y1=yy3D[4], col="red", lwd=2)
  segments(x0=xx3D[4], y0=yy3D[4], x1=xx3D[1], y1=yy3D[1], col="red", lwd=2)

  segments(x0=xx3D[5], y0=yy3D[5], x1=xx3D[6], y1=yy3D[6], col="red", lwd=2)
  segments(x0=xx3D[6], y0=yy3D[6], x1=xx3D[7], y1=yy3D[7], col="red", lwd=2)
  segments(x0=xx3D[7], y0=yy3D[7], x1=xx3D[8], y1=yy3D[8], col="red", lwd=2)
  segments(x0=xx3D[8], y0=yy3D[8], x1=xx3D[5], y1=yy3D[5], col="red", lwd=2)

  segments(x0=xx3D[1], y0=yy3D[1], x1=xx3D[5], y1=yy3D[5], col="red", lwd=2)
  segments(x0=xx3D[2], y0=yy3D[2], x1=xx3D[6], y1=yy3D[6], col="red", lwd=2)
  segments(x0=xx3D[3], y0=yy3D[3], x1=xx3D[7], y1=yy3D[7], col="red", lwd=2)
  segments(x0=xx3D[4], y0=yy3D[4], x1=xx3D[8], y1=yy3D[8], col="red", lwd=2)

}

sys3D()