Analytical shape computation of macromolecules: I. molecular area and volume through alpha shape
J. Liang, H. Edelsbrunner, P. Fu, P. Sudhakar, S. Subramaniam, Proteins: Structure, Function and Bioinformatics 33 (1998) 1–17.

Analytical shape computation of macromolecules: II. Inaccessible cavities in proteins
J. Liang, H. Edelsbrunner, P. Fu, P. Sudhakar, S. Subramaniam, Proteins: Structure, Function and Bioinformatics 33 (1998) 18–29.