8

1100 Chapter 9: Sur face Modeling
at the Surface sub-object level on the Surface
Common rollout.
•Ifyoucreatea
blend surface (page 1–1184) and
it looks like a bow tie, use Flip End 1 or Flip
End 2 to correct the twist.
• If a CV curve gives you unexpected or incorrect
results, try reparameterizing it. Click Reparam.
at the Curve sub-object level. This button is on
the CV Curve rollout. In the
Reparameterize
dialog (page 1–1238)
, choose Chord Length
reparameterization.
If the cur ve still gives you trouble, try rebuilding
it. The Rebuild button is on the same rollout.
• If a blend between a surface and a cur ve
gives you unexpected or incorrect results, try
reparameterizing the parent surface. Click
Reparam. at the Surface sub-object level. This
button is on the CV Surface rollout. In the
Reparameterize dialog (page 1–1238) ,choose
Chord Length reparameterization.
• If you see a seam in a shaded viewport, render
the view p ort first before you try to fix the seam.
What you see in v iewports might not be what
you get in a render, and the viewport shader
is less accurate than the production renderer.
Seams in v iewports can also result from
different
surface approximation settings (page
1–1241)
for the viewport and the renderer, so
check these as well.
• If you see gaps between faces in the rendered
model, increase the Merge value for the
renderer in the surface approximation settings.
• Sometimes gaps between faces appear af ter
you convert a NURBS model into a mesh. (For
example, by using
Mesh Select (page 1–710) .)
If this happens, increase the Merge va lue for the
renderer in the
surface approximation (page
1–1241)
settings.
• If you see odd twists in a
1-rail (page 1–1205)
or 2-rail (page 1–1210) sweep, add more cross
sections at the areas of change in the surface.
Forexample,ifyourraillookslikeaboxwith
rounded corners, placing cross sections at the
corners helps to control the shape of the sweep.
On the other hand, you don’t need more cross
sections for a rail shaped like an ’S’, because the
curvatureismoreconstant.
• If a U loft or UV loft doubles back on itself
unexpectedly, make sure t hat al l the curves are
going in the same direction. Click Reverse to
change a curve’s direction. Use the Start Point
spinner to align the curve’s initial points.
How to I mprove Per formance
These are tips on improv ing the performance of
your NURBS models.
• Avoid using point curves and point surfaces.
These are slower than CV cur ves and CV
surfaces. Use the point forms only when you
need them for construction; for example,
when you use Curve Fit to create a curve that
interpolates spec ific points.
•Usethe
nonrelat ional stack (page 1–1118)
feature in conjunction with the Shaded Lattice
toggle to improve performance while you
animate your NURBS mo del.
• Use Transform Degrade to hide surfaces while
you are moving, rotating, and scaling NURBS
sub-objects. The shortcut CT RL+X toggles
this option.
Yo u c a n u s e CTRL+X inthemiddleofa
transform, to turn on degradation if things are
happening slowly.
• Turn off the display of dependent surfaces
whileyouarecreatingnewdependentsurfaces
or moving, rotating, or scaling NURBS
sub-objects. The shortcut CTRL+D toggles
dependent surface display.