1. A method executed in an apparatus for generating graphics data indicating shape features of three-dimensional graphics based on X, Y and Z coordinate values, comprising the steps of: determining X and Y coordinate values of a shape specific point for specifying the shape of said three-dimensional graphics; generating a random number using the X and Y coordinate values as seeds; calculating a Z coordinate value of said shape specific point based on the generated random number; and generating said graphics data based on the Z coordinate value and the X and Y coordinate values of said shape specific point.