pXY<-ggplot(as.data.frame(bullet)) +geom_path(aes(X, Y, alpha=Z), col='green') + opts(legend.position = "none") pXY<-pXY +geom_path(data=as.data.frame(target), aes(X, Y, alpha=Z), col='blue') pXY<-pXY +geom_path(data=as.data.frame(guess), aes(X, Y, alpha=Z), col='red') print(pXY)