. . "In this case, a lump having a high contrast in the neighbor of an observation object is referred to as A, the observation object as B (there is a case that B is identical with A), and a vector determined by a projection method and a projection direction as C. Herein, C is a viewing direction in the case of parallel projection, a radial vector in the case of VE, or a vector orthogonal to the viewin" . .