a b c
In our approach to volume modeling, we combine volume representations by voxel data and by continuous real functions. The figures above illustarte:
a) sweeping by a volumetric head;
b) head cut by a moving cutter;
c) hair growth and styling on the voxel head.

One of the main problems is the function-to-voxel and voxel-to-function conversion. The following paper discusses the conversion between two representations and gives several examples of their useful combination:

Savchenko V.V., Pasko A.A., Sourin A.I., Kunii T.L.
“Volume modelling: representations and advanced operations”, Computer Graphics International '98 (June 22-26 1998, Hannover, Germany), IEEE Computer Society, 1998, ISBN 0-8186-8445-3, pp.4-13.
Electronic version: PostScript + zip (1.1 M)