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1242 Chapter 9: Surface Modeling
five algorithms. Each approximates NURBS
surfaces by tessellating them in a different way.
Generally speaking, if the preset values you have
chosen give good results, you don’t need to adjust
the controls on this rollout. Adjust them if you
encounter problems with the preset alternative.
Tips
• Viewport Tessellation: The tessellation method
creates the mesh. If you modif y the NURBS
object with Mesh Select (page 1–719),choose
the metho d that g ives the result you need. If
you use modifiers heavily, Spatial or Parametric
might be better than Curvature, because of
their regular tessellation. Curvature-dependent
tessellation can cause problems with some
modifiers.
• Renderer Tessellation: Spatial and Curvature
usually obtains the most accurate rendering.
Curvaturecanbethemoreefficientchoice
when you render animated surfaces.
Lock to Top Level —(for sub-object surfaces only)
When on, the surface sub-object uses t he same
surface approximation settings as the top-level
NURBS model, and other controls on this rollout
are disabled. When turne d off, you can set the
sub-object approxim at ion to differ from the
top-level model. Default=on.
Regular—Generatesafixedtessellationacrossthe
surface based on U Steps by V Steps. Increasing
these parameters increases accuracy at a cost of
speed, and v ice versa, but in general this can be the
quickest and least accurate way to approximate a
NURBS surface. Very low values for U and V Steps
using the Regular method usually doesn’t provide
good results. Model complexity increases slowly
as U and V Steps values increase.
Regular mesh of the NURBS teapot
Para m et r i c—Generate s an adaptive tessellation
based on U Steps by V Steps. Low val ues for U
and V Steps using the Parametric 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 tessellation made
of triangular faces.