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In three-dimensional texture mapping, each point determines its color without the use of an intermediate map shape (Peachey, 1985; Perlin, 1985). We use the (x,y,z) coordinate to compute the color directly. Itís equivalent to carving an object out of a solid substance. Most 3D texture functions do not explicitly store a value for each (x, y, z)-coordinate, but use a procedure to compute a value based on the coordinate and thus are called procedural textures.