A surface of a product is divided into a plurality of patches and a polygon mesh is formed. Sequences of vertexes on borderlines between the adjacent patches are allowed to correspond to each other, and then, a texture is mapped on each of patch units. The vertexes of the polygon mesh displaced in accordance with the mapped texture are connected together to form crimp applied polygon data for each of the patch units. In each of processing stages, since data to be processed can be limited to data of the two adjacent patches at the maximum, a practicable range of a computer is not exceeded due to the restriction of capacity of an operation memory.