Perlin Noise to Percentage

Question

I'm coding a map generator based on a perlin noise and ran into a problem:

Lets say I would want 30% water and 70% dirt tiles. With a usual random generator there is no problem:

tile = rnd.nextFloat() < 0.7f ? DIRT : WATER;

But a perlin noise is normal distributed (ranges from -1 to 1, mean at 0) so it's not that easy.

Does anyone know a way to transform a normal to an uniform distribution or a different way I could get a percentage from a noise value?

EDIT: The 70% are just an example, I'd want to be able to use any value dynamically, at best with 0.1% precision.

EDIT2: I want to transformate perlin noise to a uniform distribution, not to normal (which it already is alike).

Answer 1

If you want to get exactly 30% water (or some other specified value), you could do this.

1. Generate your height-map.
2. Place all the height-values into a list.
3. Sort the list.
4. Pick the value, that appears 30% into the list, as your water-level.