@incollection {jue:98b,
 author = {B. J{\"u}ttler},
 title = {Triangular {B}\'ezier surface patches with a linear normal vector field},
 booktitle = {The mathematics of surfaces, VIII (R. Cripps, ed.)},
 pages = {431--446},
 publisher = {Info. Geom., Winchester},
 year = {1998}
}