the linked article is wrong. that, or http://webstaff.itn.liu.se/~stegu/simplexnoise/simplexnoise.pdf http://webstaff.itn.liu.se/~stegu/simplexnoise/simplexnoi

the linked article is wrong. that, or http://webstaff.itn.liu.se/~stegu/simplexnoise/simplexnoise.pdf http://webstaff.itn.liu.se/~stegu/simplexnoise/simplexnoise.... (from euccastro's comment below) is. but the latter looks more authoritative to me and checks against http://en.wikipedia.org/wiki/Perlin_noise http://en.wikipedia.org/wiki/Perlin_noise. perlin noise is gradient noise (so the gradient is chosen at random, not the height.