@article {jue:93b,
 author = {R. Dietz and J. Hoschek and B. J{\"u}ttler},
 title = {An algebraic approach to curves and surfaces on the sphere and on other quadrics},
 journal = {Comput. Aided Geom. Design},
 volume = {10},
 year = {1993},
 pages = {211--229}
}