ABSTRACT
Bicubic patches (integral ones) have enjoyed enormous popularity. Another type of surface, the Coons patch, never became quite as popular because of problems people had with a correct specification of certain twist vectors (see [57] for details.) The twist problem was first fixed by J. Gregory in 1972, still in the context of Coons patches. What really made his idea recognized and successful was, however, a modification by Chiyokura and Kimura as described in [33] and [32], The following sections will focus on that approach; for the original literature, see Barnhill [14], Barnhill and Gregory [15], and Gregory [83].1
