9

Modifying NURBS Models and Creating Sub-Objects 1081
The direction of the curve determines the
initial direction of the trim. For example, a
closed curve on surface created in a clockwise
direction trims inward, creating a hole in the
surface; while a closed curve on surface created
in a counterclockwise direction t r ims outward,
creating a curve-shaped portion of the surface.
When a surface is trimmed, its untrimmed version
is still present in the 3ds Max scene. You can selec t
itforthepurposesofeditingit,orreplacingitasa
parent to a dependent sub-object (page 1–1087).To
do so, use the Select Objects dialog. See Sub-Object
Selection (page 1–1084).
Pr ocedur es
Example: To cut a hole in a CV sur face:
1.
Create a CV surface in the Top v iewport.
2. Create a closed CV curve sub-object that lies on
top of (or abov e) the surface.
3. In the toolbox, turn on Normal Projected
Curve, then in the Top view port select first the
CV curve, then the surface.
This creates a projection of the CV curve that
lies on the surface, and can trim it.
4. In the normal projected cur ve’s parameters,
click to turn on Trim.
Aholeappearsinthesurface. Dependingon
the orientation of the Normal Projected curve,
you m ight see everything but the hole.
5. UsetheFlipTrimtoggletoinvertthetrim.
Note: Trims aren’t displayed in viewports if the
NURBS surface’s Surface Trims toggle is turned
off on the General rollout’s Display group box.
Above: CV curve on surface
Below left: Using the curve to trim the sur face
Below right: Using Flip Trim to change the trimming
direction
To select a n untrimmed sur f ace:
1.
Mak e sure the Keyboard Shortcut Override
toggle (page 3–872) is on.
2. At the appropriate sub-object level or during a
replace p arent operation, press
H .ASelect
Objects dialog (page 1–78) appears.
3. If the untrimmed version is selectable at this
level, the tr immed version appears as a "tree,"
w ith a plus sign next to it. Click the plus sign to
expandthetree. Thechildistheuntrimmed
version. Highlight its name to select it.
Modify ing NUR BS M odels and
Cre atin g Su b - O b jects
You can edit NURBS immediately when you
enter the Modify panel. You don’t have to apply
a modifier, as you do for most kinds of 3ds Max
objects.
WhileyouareeditingaNURBSobjectonthe
Modify p a nel, you can create sub-objects "on the
fly," without having to go back to the Create p anel.
This is an exception to the way you usually use
3ds Max. The Modif y panel for NURBS curve and