200 * cos(((xval-(res/2))/3)*((yval-(res/2))/3))here's another:
400*cos(((xval-(res/2))/2)) * sin(((yval-(res/2))/2))and finally the one from the gensurf website (modified):
5000-(radius/16+256*sin(radius/256))i just looked at gensurf and because it is incompatible with newer versions of Excel so the formula function doesn't work, it seems pretty useless. besides, Twister's purpose is different to gensurf's, except for heightmaps.