CG Modeling 2: NURBS - An Introduction to Computer Graphics for Artists - page 265

Fig. 14.29 Patches 1 , 2 , 3 , and 4 are curvature continuous where they meet. When rendered ( right )
there is no discernible break between them

Fig. 14.30 A slightly displaced CV causes a strong dent in the surface on right

location by providing a set of control points that serve to absorb the weight of control
vertices that come before or after them and smoothing the tangent fl ow into the next
curve. This results in a fi ve-degree curve. If it had three control points on either side,
it would be a seven-degree curve.
Curvature continuity is desirable for manufacturable surfaces or objects that will
be rendered at high resolution in close-up (Fig. 14.29 ). Curvature continuity requires
additional modeling effort and is not recommended for most projects, particularly
in CG animation for games, fi lm, or television advertisements.

14.4.11 Surface Sensitivity

One of the fi rst things you will notice after you build a surface from curves is that
small changes to the curves it is built from have a powerful effect on the sur-
face. A control vertex has a more powerful effect because it is not just the CV
position that is adjusted, but also a tangent that may not be displayed (Fig. 14.30 ).