9

1098 Chapter 9: Surface Modeling
into an actua l displaced mesh so you can see the
effect of displacement in viewports. To make a
displaced mesh copy of the NURBS model, use
Snapshot (page 1–453).
Connecting a n Ar m to a Shoul der
• The easiest approach is to create a CV curve on
surface (page 1–1172) or normal projected curve
(page 1–1169) on the shoulder. Then create the
arm as a U loft (page 1–1196).Forthelastcurve
oftheUloft,selecttheCVcurveonsurfaceor
the normal projected curve. Then turn on Use
COS Tangents, w hich m akes the loft surface
tangent to the other surface where the arm joins
the shoulder.
• If the blend appears twisted, use the Start Point
spinner to change the location of the first point
of the curves that make up the U loft surface.
• Another way to connect a U loft to another
surfaceistoprojectthelastcurveintheU
loft onto the other surface. Click Make COS
to convert the projected curve in to a curve on
surface, and then on the U Loft Surface rollout
click Insert to make the new curve on surface
the last cur ve in the U loft. You can scale the
cur ve on surface or move its C Vs to get the
cur v ature and blending you want.
How to Fix NUR BS Objects
These are tips on fixing problems w ith NURBS
models.
• Ifyoucreateasurfacebutitisn’tvisiblein
viewports, click Flip Normals. Flip Normals is
availableonthesurface’screationrollout,or
at the Surface sub-object level on the Surface
Common rollout.
•Ifyoucreateablend surface (page 1–1183) and
it looks like a bow tie, use Flip End 1 or Flip
End 2 to correct t he twist.
•IfaCVcurvegivesyouunexpectedorincorrect
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 1–1237), choose Chord Length
reparameterization.
If the curve still gives you trouble, try rebuilding
it. The Rebuild button is on the same rollout.
• If a blend b etween a surface and a curve
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 1–1237),choose
Chord Length reparameterization.
• If you see a seam in a shaded view port, render
the viewport first before you try to fix the seam.
What you see in v iewports mig ht not b e what
you get in a render, and the viewport shader
is less accurate than the production renderer.
Seamsinviewportscanalsoresultfrom
different surface approximation settings (page
1–1239) 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 after
you convert a NURBS model into a mesh. (For
example, by using Mesh Select (page 1–719).)
If this happens, increase t he Merge value for
the renderer in the surface approximation (page
1–1239) sett ings.
• If you see odd twists in a 1-rail (page 1–1204)
or 2-rail (page 1–1209) sweep, add more cross
sections at the areas of change in the surface.
Forexample,ifyourraillookslikeaboxwith
rounded corners, placing cross sections at the
corners hel ps to control the shape of the sweep.
On the other hand, you don’ t need more cross