title: Fractal mountains using Sierpinski gasket in OpenGL
body: <p>I'm reading a book on OpenGL, "Interactive Computer Graphics" by Edward Angel. In it, he asks you to modify a Sierpinski gasket algorithm to yield fractal mountains. To do so, it says to find the midpoint of each side, then perturb this location before subdivision. He doesn't explain at all how to "perturb" the location, and looking online yielded no results.</p>
  
  <p>Can anyone explain what this means? </p>
  
  <p>Thanks!</p>