Graphics Programs Reference
In-Depth Information
FIGURE 23.49
The Surface Asso-
ciativity panel
in the Properties
Inspector palette
You can select Remove to remove associativity altogether or select None to limit the associa-
tivity to the set of objects currently associated with the surface model. Once you change this
setting, you can't return to a previous setting except with an Undo.
CONSTRAINTS, SURFACES, AND ASSOCIATIVITY
In Chapter 16, “Making “Smart” Drawings with Parametric Tools,” you learned that you can add
constraints to objects to control their behavior. With Surface Associativity turned on, you can
extrude constrained objects and the resulting surface will also follow the constraints of the source
2D objects. But remember that if you use constraints with 3D surfaces in this way, you need to care-
fully plan the way you build your model to make effi cient use of constraints.
Editing with Control Vertices
So far you've been creating
procedural surfaces
, which are surfaces that allow you to take advan-
tage of associativity. AutoCAD also allows you to create
NURBS surfaces
. You may recall that
splines are also NURBS, so you might think of a NURBS surface as a kind of 3D surface spline.
Splines allow you to move, add, or subtract control vertices, or CVs, and you can control the way
the CVs “pull” on the curve of the spline. Likewise, NURBS surfaces allow you to add or remove
CVs and adjust the direction and force of the CVs.
There are two ways to create a NURBS surface. You can turn on the NURBS Creation option
by typing
SURFACEMODELINGMODE
↵
1
↵ and then go about creating your 3D surfaces.
Any 3D surface you create with this option turned on will be a NURBS surface.
C
O N V E R T I N G
A
S
U R F A C E
T O
A
NURBS S
U R F A C E
You can convert an existing surface to a NURBS surface by typing
CONVTONURBS
↵. This
tool also converts 3D solids and meshes. To use it, follow these steps:
1.
Open the CVedit1.dwg sample file, which can be obtained from the topic's companion
website.
