title: plot cylindrical coordinate using an x y file in gnuplot
body: <p>I would like to make a 3D plot with gnuplot using the interface.txt file (<a href="https://drive.google.com/file/d/1ahFuIGPwOZt0zZHc0vPOMxOwt3K_MpQf/view?usp=sharing" rel="nofollow noreferrer">File</a>).
  Knowing that I have a y-axis rotation invariance.
  This figure represents a 2D section (plot 'interface.txt' u 2:1) <a href="https://i.stack.imgur.com/193vT.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/193vT.png" alt="2D section"></a></p>
  
  <p>Here's what I'd like to have with gnuplot but I don't know how to plot it.
  I would like to get this picture but for theta = [0:2*pi].
  <a href="https://i.stack.imgur.com/XhcdA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XhcdA.png" alt="enter image description here"></a>
  I tried this code but for now i don't know how to plot it</p>
  
  <pre><code>reset
  set angles degrees
  set mapping cylindrical
  
  splot for [t=1:360:2] 'interface.txt' u t:1:(sqrt($2**2+$1**2))
  </code></pre>
  
  <p>If you have any idea ?
  Thanks you !</p>