1. A method for generating boundary surface information using a computer, the method comprising the steps of: an input step of inputting information on a boundary surface of an object to the computer; a grid sampling step of determining cutting points and normal vectors of the boundary surface at the cutting points, the cutting points being points at which the boundary surface cuts across edges of a predetermined rectangular parallelepiped grid, and storing the cutting points and the normal vectors in a storage unit as primary data; a D-polyhedron data generation step of connecting adjacent cutting points with a line segment to form a triangle one by one for generating D-polyhedron data constituted of triangles only; and a V-polyhedron data generation step of generating V-polyhedron data constituted of intersections of a plurality of infinite planes passing through the cutting points and whose normals coincide with the normal vectors; wherein any one of the D-polyhedron data and the V-polyhedron data is generated from the primary data, and the other is generated as a dual of the one.