Fractal mountains using Sierpinski gasket in OpenGL

Question

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.

Can anyone explain what this means?

Thanks!

Answer 1

Here's a thought: "perturb" the midpoint by displacing it in the direction perpendicular to the side and form a small hat-shaped segment.

Go from this:

______

to this:

__/\__

Answer 2

By "perturb" he likely means adding a bit of noise to the new midpoint.