How is a 3d perlin noise function used to generate terrain?

Question

I can wrap my head around using a 2D Perlin noise function to generate the height value but I don\'t understand why a 3D Perlin noise function would be used. In Notch\'s blog, h

Answer 1

Well, Minecraft is about Mines. So, what Notch tried to solve was: "How do I get holes / overhangs in my world?"

Since 2D perlin noise generates nice/smooth looking hills, 3d perlin noise will generate nice/smooth hills and nice holes in your 3D voxel grid.

An implementation can be found here (while that is an N-dimensional solution).

In other use-cases the Z component of a 3D perlin noise is set to the current time. This way you will get a smooth transition between different 2d perlin noises and that can be used as groundwork for fluid textures.