8

1210 Chapter 9: Sur face Modeling
Sweep Parallel—
When on, ensures that the sweep
surface’snormalisparalleltotherail.
Snap Cross-Sections—When on, cross-section
curves are translated so they intersect the rail.
The first cross sect ion is translated to the start of
the rail, and the last to the end of the r ail. The
crosssectionsinthemiddlearetranslatedto
touch the rail at the closest point to the end of the
cross-section curves.
When Snap Cross-Sections is on, the sweep
follows the rail cur ve exactly. This makes it easier
to construct 1-rail sweep surfaces.
Road-Like—When on, the sweep uses a constant
up-vector so the cross sect ions twist uniformly
as they tr avel along the rail. In other words, the
crosssectionsbanklikeacarfollowingaroad,ora
camera following a
path constraint (p age 2–380) .
Default=off.
Whenyoueditthesurface,youcancontrolthe
angle of banking . The up-vector is displayed as
a yellow gizmo (similar to the gizmo that
lathe
surfaces (page 1–1192)
use for the center of
rotation). To change the up-vector angle, use
Rotate (p age 1–420) to change the gizmo’s angle.
Display I so Curv es—When set, the 1-ra il s weep’s
V-axis iso curves are displayed as well as the
U-axis curves used to construct the loft. The
V-axis curves are only for display. You can’t use
them for surface construction.
Edit Cur ves—Lets you edit the currently selected
curve without switching to another sub-object
level. ClicktoturnonEditCurve. Thepoints
or CVs of the curve are displayed, as well as the
control lattice if the curve is a CV curve. You can
now transform or otherwise change the points
or CVs as if you were at the Point or Curve CV
sub-object level. To finish editing the curve, click
to turn off Edit Curves.
Tip: When you edit curves in a 1-rail sweep,
turning off display of the sweep itself can make the
cur ves easier to see and improve per formance. Use
CTRL+D (while the
Keyboard Shortcut Override
Togg le (page 3–912)
is on) to toggle display of
dependent sub-objects, including sweeps.
Thesweepsurfacecandeviatefromthecurve
if you edit a cur ve in a s weep by increasing the
weight of the curve CVs. You can work around
this by refining the curve at the point where the
surface deviates.
2-R ail Sweep Sur face
Select NURBS object. > Modify panel > Create Surfaces
rollout>DependentSurfacesgroupbox>2-Rail
Select N URBS obj ect. > Modify pane l > NURBS toolbox >
Create 2-Rail Sweep button
Sweep sur faces are constructed from curves. A
2-rail sweep surface uses at least t hree curves.
Two curves, the "rails," define the two edges of
the surface. The other curves define the surface’s
crosssections.A2-railsweepsurfaceissimilarto
a 1-rail sweep. The additional rail gives you more
control over the shape of the surface.
Sweep surface created with two rails
The cross-section curves should intersect the rail
curves. If the cross sect ions don’t intersect the
rails, the resulting surface is unpredictable. In
addition, the initial points of the rails and the