8

1088 Chapter 9: Sur face Modeling
Above: Weights=0.0
Below: Weights=40.0
Changing a sphe r ic al su rface by de c reasing or increasing
the weight of four CVs (selected CVs are at the left, in red)
Wei g ht s ca n be a use f u l way to "t u ne " th e
appearance of a NURBS cur ve or surface.
The weight value of a CV is r ational (as in a
"rational number"). That is, it is relative to other
CVs in the curve or surface. Changing the weight
of all CVs at once has no effect, because it doesn’t
change the ratio between weights.
Points,PointCurves,andPointSurfaces
Point curves and point surfaces are similar to CV
curves and surfaces, but the points that control
them are required to lie
on the curve or surface.
Unlike CVs, points do not have a weight.
Point curves and point surfaces can be more
intuitive to create and work with. However,
workingwithpointsub-objectsisslowerthan
working with CV sub-objects. You can thin k of a
point curve or point surface as being dependent
on the points to which it fits.
Pointsthatyoucreateindividuallyarethesameas
the points on point curves and surfaces, except that
initially they aren’t part of a curve or surface. You
cancreateapointcurvebyfittingittopointsthat
you select. When you fit the new point curve, you
can use points that are part of curves or surfaces,
and individual point sub-objects.
Depen dent S ub-Obj ects
NURBS sub-objects are either independent or
dependent. A dependent sub-object is base d on
the geometry of other sub-objects. For example,
a blend surface smoothly connects two other
surfaces. Transforming or animating either of
the ori ginal, parent surfaces causes the shape of
the blend to change as it maintains a connection
between the parents.