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1244 Chapter 9: Sur face Modeling
Regular mesh o f the NURBS teapot
Par amet r ic—Generates an adaptive tessellation
based on U Steps by V Steps. Low values for U
and V Steps using the Parametr ic method often
provide good results. Model complexity increases
rapidlyasUandVStepsvaluesincrease,so
take care when you switch from Regular , which
generally requires higher U and V values, to
Parametric, where lower U and V values generally
suffice.
For example, if you convert a teapot to NURBS and
set the U and V steps to 15, the Regular method
generates 4470 faces but the Parametric method
generates 204960 faces.
Parametric mesh of the NURBS teapot
Spatial—Generates a uniform tessellat ion made
of triangular faces.
TheEdgeparameterspecifiesthemaximum
length of a triangular face in the tessellation. The
valueisapercentageoftheobject’sbounding
box. Decreasing this value increases accuracy but
increases rendering time.
Spatial mesh of the NURBS teapot
Curvature—( T he default.) Generates a var iable
tessellation based on the curvature of the surface.
The tessellation has a finer gr ain where the surface
is more curved. Changing surface curvature
dyna mically changes the curvature tessellation.
The Distance p arameter specifies how far the
approximation can deviate from the actual NURBS
surface. Distance is a percen tage of the diagonal of
each surface’s bounding box. Each surface in an
object is tessellated based on its size, independently
of other surfaces. Scaling a surface doesn’t change
its tessellation. Decreasing this value increases
accuracy but increases rendering time. When
you set Distance to 0.0, the software i gnores this
parameter and uses the Angle to control accuracy.
The A ngle p arameter specifies the m ax imum angle
between faces in the approximation. Decreasing
this value increases accuracy but increases
rendering time. When you set Angle to 0.0, the
software ignores this p ar ameter and uses Distance
to control accuracy.