@article{Bangert1999AGeometric, Author = {Claudia Bangert and Hartmut Prautzsch}, Title = {A Geometric Criterion for the Convexity of Powell-Sabin-Interpolants and its Multivariate Generalization}, Journal = {Computer Aided Geometric Design}, Year = {1999}, Volume = {16}, Number ={6}, Pages = {529–-538} }