@Article{PU00,
author  = {Hartmut Prautzsch and Georg Umlauf},
title   = {A $G^1$ and a $G^2$ subdivision scheme for trinagular nets}, 
journal = {International Journal on Shape Modelling},
year    = 2000,
volume  = 6,
number  = 1,
pages   = {21-35}
}