How to create/enhance my own radar/polar chart without additional packages in R?

Question

I've been trying to create a combination of radar/polar chart of a given vector of polygon vertices, without packages, but just with base R, which I really struggle with. So far, with some help, I have reached the following point:

a <- a <- abs(rnorm(5, mean = 4, sd = 2))
names(a) <- LETTERS[1:5]
stars(matrix(a,nrow=1),axes=TRUE, scale=FALSE,col.lines="blue",radius=FALSE)
center <- c(x=2.1, y=2.1) #the starchart for some reason chooses this as a center
half <- seq(0, pi, length.out = 51)
angle=45
for (D in a) {
  Xs <- D * cos(half); Ys <- D * sin(half)
  lines(center["x"] + Xs, center["y"] + Ys, col = "gray", xpd = NA, lty="dashed")
  lines(center["x"] + Xs, center["y"] - Ys, col = "gray", xpd = NA, lty="dashed")
}

which gives me something this:

What I would need to take further is:

• center this mixed radar/polar chart at (0,0) and mark the center
• color the polygon area transparently
• add radii starting from the outermost circle and reaching the center through the polygon vertices
• put the vector name labels on the ends of the radii on the outermost circle

So, the final result should look something like this:

I have experimented with the polygon(), symbols() functions and par() graphic parametres, but I am really struggling to combine them...My problem is that I don't understand how the stars() function plot coordinates selection relates to my input.

Answer 1

Did not liked the stars functions... so I made a full rondabout with polygon:

polar_chart <- function(values){
  k <- length(values)
  m <- max(values)
  # initialise plot
  plot(1, type="n", xlab="", ylab="", xlim=1.2*m*c(-1,1), ylim=1.2*m*c(-1,1))
  # radial lines & letters
  sapply(k:1, function(x){
    text(1.1*m*cos(-(x-1)*2*pi/k + 2*pi/3), 1.1*m*sin(-(x-1)*2*pi/k + 2*pi/3),
         LETTERS[x], cex = 0.75)
    lines(c(0, m*cos((x-1)*2*pi/k + 2*pi/3)), c(0, m*sin((x-1)*2*pi/k + 2*pi/3)),
          col = "grey",lty="dashed")
    })
  # circles
  aux <- seq(2*pi + 0.1, 0, -0.1)
  sapply(values, function(x) lines(x*cos(aux), x*sin(aux), col = "grey",lty="dashed"))
  # polygon
  x <- values*cos(-(1:k-1)*2*pi/k + 2*pi/3)
  y <- values*sin(-(1:k-1)*2*pi/k + 2*pi/3)
  polygon(c(x, x[1]),c(y, y[1]), col = "red", border = "blue", density = 50)
}

values <- abs(rnorm(5, mean = 4, sd = 2))
polar_chart(values)

And returns a plot like the following: