@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}
}