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 How it works
 Generating the density function The first step to defining the density function f=f(x,y,z) is prescribing the base or primary shape. The primary shape determines the initial values of all points in the voxel volume. A typical primary shape is the plane, where for a plane normal to the y-axis the density function f = -y. The selection of the iso-value determines where the unmodified primary mesh would be generated. Density values less than this iso-value designate above a solid surface whereas values greater than this iso-value imply inside a solid. Other primary shapes include: Cubes Spheres Cylinders Cones Torus Voxelized models   Volumetric modifiers Volumetric modifiers are functions that are applied by the user to alter density field values. Modifiers can affect the entire volume or just user-defined regions. A region is itself a volumetric modifier that nests modifiers specific to a user constrained volume. Modifiers are classed into three categories:   Surface generation Once the values of the density volume are known an iso-surface is extracted using Marching Cubes. Marching Cubes is an algorithm for extracting a polynomial of an iso-surface from a three-dimensional scalar field. Essentially taking the values from the eight corners of a cube (the voxel) the algorithm determines the polygons necessary to represent the iso-surface passing through the cube. References http://en.wikipedia.org/wiki/Marching_cubes