Benjamin Schmitt Alexander A. Pasko Christophe Schlick Constructive sculpting of heterogeneous volumetric objects using trivariate B-splines. 130-148 2004 20 The Visual Computer 2-3 http://dx.doi.org/10.1007/s00371-003-0236-9 db/journals/vc/vc20.html#SchmittPS04