title: Symmetrical axis labels for polar plot
body: <p>I'm looking for a way to plot axis like on picture below, using ggplot2. (maybe some tips in <code>theme</code> or <code>scale_x_continuous</code>?)</p>
  <p><a href="https://i.stack.imgur.com/4Fro2.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4Fro2.jpg" alt="enter image description here" /></a></p>
  <p>I mean a symmetrical sequence of labels, which goes from 100 to 100 in this example with the center at 20 (not a horizontal orientation for the axis).</p>
  <p>Reproducible example:</p>
  <pre><code>library(ggplot2)
  required(grid)
  ggplot(data = i, aes(x = wd, y = co2)) +
    ggtitle(&quot;CO2&quot;)+
    geom_point(size=4, colour = &quot;red&quot;)+
    geom_linerange(aes(ymax =ci2, ymin=ci1), colour = &quot;red&quot;, size = 2)+
    coord_polar()+
    
    geom_hline(yintercept = seq(365, 405, by = 5), colour = &quot;grey&quot;, size = 0.2) +
    geom_vline(xintercept = seq(0, 360, by = 22.5), colour = &quot;grey&quot;, size = 0.2) +
    scale_x_continuous(limits = c(0, 360), expand = c(0, 0), 
                       breaks = seq(0, 359.99, by = 22.5), 
                       labels=c(&quot;N&quot;,&quot;NNE&quot;,&quot;NE&quot;,&quot;ENE&quot;,&quot;E&quot;,&quot;ESE&quot;,&quot;SE&quot;,&quot;SSE&quot;,
                                &quot;S&quot;,&quot;SSW&quot;,&quot;SW&quot;,&quot;WSW&quot;,&quot;W&quot;,&quot;WNW&quot;,&quot;NW&quot;,&quot;NNW&quot;)) +
    scale_y_continuous(limits = c(365, 405), breaks = seq(365, 405, by = 10)) +
    
    theme_bw() +
    theme(panel.border = element_blank(),
          panel.grid  = element_blank(),
          legend.key = element_blank(),
          axis.ticks = element_line(colour = &quot;grey&quot;),
          axis.ticks.length = unit(-1, &quot;lines&quot;),
          axis.ticks.margin = unit(1.3,&quot;lines&quot;),
          axis.text =  element_text(size=24),
          axis.text.y = element_text(size=24),
          axis.title = element_blank(),
          axis.line=element_line(),
          axis.line.x=element_blank(),
          axis.line.y = element_line(colour = &quot;grey&quot;),
          plot.title = element_text(hjust = 0, size = 20))
  </code></pre>
  <p><a href="https://i.stack.imgur.com/WTslw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WTslw.png" alt="enter image description here" /></a></p>
  <p>Data:</p>
  <pre><code>i &lt;- structure(list(wd = c(0, 112.5, 135, 180, 202.5, 22.5, 225, 247.5, 
  270, 292.5, 337.5, 45, 67.5, 90), co2 = c(389.82, 376.82, 386.06, 
  392.04, 392.55, 387.97, 391.45, 389.87, 390.12, 389.68, 391.39, 
  390.1, 386.89, 383.05), ci1 = c(388.37, 367.67, 378.98, 381.76, 
  388.63, 386.65, 388.32, 388.5, 389.03, 387.25, 389.05, 388.65, 
  385.64, 381.1), ci2 = c(391.26, 385.98, 393.15, 402.31, 396.46, 
  389.28, 394.58, 391.23, 391.21, 392.12, 393.73, 391.55, 388.15, 
  385.01)), row.names = c(NA, -14L), class = &quot;data.frame&quot;)
  </code></pre>