8

1174 Chapter 9: Sur face Modeling
CV Curv e o n Su rface
Selec t NURBS object. > Modify panel > C reate Curves
rollout > Dependent Curves group box > CV on Surf
button
Select NU RB S object. > Modify panel > NURBS toolbox >
Create CV Curve on Surface button
A CV curve on surface is similar to a plain CV
curve,butitliesonasurface. Youcreateitby
drawing rather than projecting from a d i fferent
cur ve. You can use this c urve ty pe for
trimming
(page 1–1082)
the surface on which it lies.
TrimmingasurfacewithaCVcurveonsurface
There are two methods for drawing and editing
cur ves on surfaces: draw ing in a viewport, or
using the Edit Curve on Surface dialog. The choice
is useful b e cause you draw in two dimensions, with
a mouse or other pointing device, while the curve
on a surface can exist in three dimensions. The
more complex the 3D surface, the more effort it
can require to create and edit a curve on a surface.
Visual feedback can help you draw the curve. T he
point whose surface you first click is shown as a
blue square, and the surface’s minimum UV point
is shown a s a plus sign (+). As you draw the curve,
it is displayed interactively in viewports.
Dra wing in a Vi ewpor t
When you click to position a CV, the click is
projected in the viewport’s Z dimension. That is,
your click is projected "through the screen" and
ontothesurface.Thisisastraightforwardwayto
create a curve on a surface if the portion of the
surfacewherethecurvewilllieisclearlyvisiblein
the viewpor t. However, this method doesn’t let
you place CVs on surface locations that are not
visible in the viewport (they are on back faces, lie
behind other geometr y, and so on).
Using the Edi t Cur ve on S ur f ace Di alog
The
Edit Curve on Surface dialog (page 1–1230)
letsyoueditcurvesonsurfacesasyoueditregular
curves in a viewport. The main par t of the dialog
is a two-dimensional view of the surface. The
controls provide typical curve editing functions.
WhileyouarecreatingaCVcurveonsurface,the
2D View toggle controls displa y of the Edit Curve
on Surface dialog.
You can edit the CVs in CV curves on surfaces
at the
Curve CV sub-object level (page 1–1128)
,
as you edit other kinds of curve CVs. You can
transform CVs in CV curves on surfaces, but
you c an’t move the CVs off the surface. Using
the Curve CV sub-object level is an alternative
toeditingtheseCVsbyusingtheEditCurveon
Surface dialog.
Procedure
To create a CV curv e on s ur f a ce:
1.
In a NURBS object that contains at least
onesurface,turnonCreateCVCurveon
Surface in the NURBS toolbox, or CV on Surf
on the Create Curves rollout.
2. Do one of the following:
•Drawthecurveintheviewport,usingthe
mouseabovethesurface.
Turnon2DView. ThisdisplaysanEdit
Curve on Surface dialog, which lets you
create the curve in a two-dimensional (UV)
representation of the surface.
3. Right-click to end curve creation.