8

Surface Approximation Rollout 1251
Note:
When Viewports is chosen, you must also
choose Mesh Only in order to see the effec t of the
Mesh Parameter settings in w ireframe view por ts.
Generally speaking, if the preset values you have
chosen give goo d results, you don’t need to adjust
the controls in this rollout further. Use them if you
encounter problems with the preset alternative.
Tips
• Viewport Tessellation: The tessellation method
creates the mesh, so if you modify the NURBS
object with Mesh Select, choose the method
that gives the result you n eed. 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 obtai ns the most accurate rendering.
Curvaturecanbethemoreefficientchoice
when you render animated surfaces.
Regular—Generatesafixedtessellationacrossthe
surface based on U Steps by V Steps. Increasing
these p arameters increases accurac y at a cost of
speed, and vice 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.
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 Paramet r ic method
generates 204960 faces.
Parametric mesh of the NUR BS teapot
Spatial—Generates a uniform tessellation 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—Generates a variable tessellation based
on the curvature of the sur face. The tessellation
hasafinergrainwherethesurfaceismorecurved.