A shell map is a bijective mapping between shell space and texture space that can be used to generate small-scale features on surfaces using a variety of modeling techniques. The method is based upon the generation of an offset surface and the construction of a tetrahedral mesh that fills the space between the base surface and its offset. By identifying a corresponding tetrahedral mesh in texture space, the shell map can be implemented through a straightforward barycentriccoordinate map between corresponding tetrahedra. The generality of shell maps allows texture space to contain geometric objects, procedural volume textures, scalar fields, or other shell-mapped objects.
Serban D. Porumbescu, Brian Budge, Louis Feng, and Kenneth I. Joy, “Shell Maps”, ACM Transactions on Graphics: Proceedings of SIGGRAPH 2005, 24(3), 626-633.