CG Modeling 2: NURBS - An Introduction to Computer Graphics for Artists - page 261

Fig. 14.22 To build this bicycle quick release lever, the surfaces have to be built in a specifi c order,
as shown

Fig. 14.23 The two orange curves that are the basis for this surface are both pointing in the same
direction. The result is a clean surface

curves with mismatched directions (Figs. 14.23 and 14.24 ). Any further editing
should require either the addition of new surfaces or the cutting away of existing
ones with trim borders.

14.4.6 Curve Direction

The two orange curves (Fig. 14.24 ) are not pointing in the same direction, causing the
start and endpoint connections to be reversed and a faulty surface created. This is con-
ceptually the same as a polygonal bow-tie face, but with much greater complexity.