9

1120 Chapter 9: Surface Modeling
Cr eating and Editing NURB S
Sub-Objects
Attaching and Impor ting 3 ds Ma x
Obj ects
Modify panel > Select NURBS object. > General rollout >
Attach button, Import button, and related controls
There are two ways to bring other 3ds Max objects
into a NURBS object:
•Attach,whichworkslikeAttachformeshes
and splines. It conver ts the attached object to
NURBS format. Once the object is attached,
you can edit it as a NURBS surface or curve.
However, the attached object’s history is lost.
Note: For NURBS surfaces, you can attach
other NURBS objects, standar d primitive (page
1–170) objects, or quad patch (page 1–994) and
tri patch (page 1–995) surfaces. The patch is
converted to a NURBS surface. Quad patches
conv ert more successfully than Tri Patches. A
converted Tri Patch has a collapsed internal
edge, which gives ir regular results when you
manipulate its mesh.
When you convert a spline circle (page 1–273)
to a NURBS curve, the direction of the curve
is reversed. This facilitates using the curve to
trim a surface: if the direction weren’t reversed,
usually the circle would trim outward instead
of inward.
• Import, which works somewhat like the
operand of a Boolean (page 1–338).Theobject
is brought into the NURBS object without
losing its history. You can select the imported
object as a sub-object.
Using Import s
Here are reasons to use Import instead of Attach:
• To maintain paramet ric control over primitives.
For example, if you import a sphere, you can
change its radius directly, which you can’t do
after using Attach.
• TouseBeziersplinesasNURBScurves.
For example, if you want to use a Bezier spline
asacurveinaNURBSmodel,importit.This
allows you to edit it as a Bezier spline, and not
as a N URBS curve.
Surfaces and curves created by an import are
available in the NURBS model. For example, if
youimportabox,youcancreateablendsurface
between one of its polygons and another surface
in your NURBS object.
Once you have imported an object, the NURBS
object has an Imports sub-object level. When you
select an import, it is highlighted in red.
It is an error to apply a modifier to an import when
the modifier converts the import into something
that can’t be converted to a NURBS object. For
example, if you import a sphere and apply a Bend
(page 1–560) to it, the sphere converts to an
editable mesh, which can’t automatically convert
to a NURBS surface. In this case, the import
sub-object is in an error state, and it is displayed in
the error color (orange by default).
Imports are displayed in two different ways.
WhileyouworkattheNURBSobjectlevelorata
sub-object level other than Imports, imports are
displayed as NURBS curves or surfaces, and use
the NURBS object’s mesh tessellation (see Surface
Approximation (page 1–1239)). However, at the
Imports sub-object level, the selected import is
displayed using its native display format. In other
words, it displays as it would if it were a top-level
object.Thisisbecausethedisplaymustletyouedit
the imported object. For example, an imported
Bezier spline needs to display its tangent handles.
Thiswouldn’tbepossibleifitweredisplayedas