title: Making curved text on coord_polar
body: <p>I want make curved text around ggplot with coord_polar. I have data.frame:</p>
  
  <pre><code>z &lt;- data.frame( a=c("sensor 1","sensor 2","sensor 3","sensor 4","sensor 5","sensor 6","sensor 7","sensor 8"),  b=c(50, 60, 70, 20,90,110,30,100))
  </code></pre>
  
  <p>And here is code where I create my ggplot:</p>
  
  <pre><code>cxc &lt;- ggplot(z, aes(x=a, y=b, fill=factor(b))) + 
      geom_bar(width = 1,stat="identity",colour = "black")
  cxc + coord_polar() + 
    theme_linedraw() +theme(axis.ticks =element_blank(), axis.text.y =element_blank(), axis.title=element_blank(), axis.text.x=element_text(size = 12,angle = 45)) 
  </code></pre>
  
  <p>Here is image from my result. I want making texts (x axis): sensor 1, sensor 2... making curved like I draw with red color around circle from coord_polar. Must fit with circle. 
  <a href="https://i.stack.imgur.com/QgOoc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QgOoc.png" alt="enter image description here"></a></p>