title: R: How to : 3d Density plot with gplot and geom_density
body: <p>I'm trying to combine multiple density plots with overlay.
  ggplot and geom_density do the job, but the densities are stacked on top of each other.<img src="https://i.stack.imgur.com/GAj0B.png" alt="This is overlaid but not 3d"></p>
  
  <pre><code>ggplot(all.complete, aes(x=humid_temp)) +  
    geom_density(aes(group=height, colour=height, fill=height.f, alpha=0.1)) + 
    guides(fill = guide_legend(override.aes = list(colour = NULL))) +
    labs(main="Temperature by Height", x="Temperature", y="Density")
  </code></pre>
  
  <p>Something similar to this is what I'm trying to achieve:
  <img src="https://i.stack.imgur.com/DBfLt.jpg" alt="Density? with 3d overlay"></p>
  
  <p>In my case, the years would be substituted by height.</p>
  
  <p>Thanks!!!</p>