8

Creating NU RBS Surf aces from Geometric Primitives 1117
Procedure
To tur n a spline into NURB S cur ves:
1.
Create the spline.
2. Go to the Modif y panel.
3. In the stack display, r ight-click the name of the
spline.
4. Onthepop-upmenu,chooseConvertTo:
NURBS.
The spline is converted to one or more CV
cur ves.
Smoothly curved splines, such as circles and
arcs, convert to a single CV curve.
Splineswithsharpangles,suchasrectangles
and stars, convert to multiple CV curves w hose
endpointsareattheanglesintheoriginal
spline. These endpoints are fused except for the
initi al CV in the spline (for a star, the initial
segment is unfused at both ends).
"Sharp angles" doesn’t apply to smooth splines
to which you have g iven angles by changing
vertex tangents using t he
Edit Spline (page
1–671)
modifier. These still convert to a single
NURBS curve.
Cre ating NURBS Su rfaces fro m
Geometric Primitives
Primitive objects become NURBS surfaces that you can th en
edit in various ways.
Yo u c a n t u r n a standard primitive (page 1–165)
into a NURBS object formed of CV surfaces (page
1–1180)
. Once converted, you can no longer edit
theobjectparametrically,butyoucanedititasa
NURBS object, moving CVs and so on.
Youcan’tconvertmostextendedprimitiveobjects
in this way, but you can conv ert the
torus knot
(page 1–184)
and prism (page 1–200) extended
primitives to NURBS objects.
Yo u c a n a l s o c o n v e r t
patch (page 1–980) objects
and
loft (page 1–347) compound objects.
Tips
• Geospheres are good for creating rounded
models with no sharp edges.
• Boxes are good for creating models that have
sharp edges.
• Flattened cones work well for models whose
contours are roughly triangular.
If the primitive is closed, the converted surface is
a closed C V surface, which has no visible seams.
Also, relational
cap surfaces (page 1–1196) are
used to cap sur faces that aren’t closed.