9

1240 Chapter 9: Surface Modeling
Surface Approx imation Per Sur face
By default, sur face sub-objects use the same
approximationsettingsasthetop-levelNURBS
model. You c a n override these settings.
Each surface sub-object now has a Surface
Approximation rollout of its own. The controls
on this rollout are disabled unless you turn off
the Lock to Top Level togg le. With this toggle
turned off, you can choose approximation settings
specific to this surface sub-object.
Inter face
Tessellation group
Viewports—When chosen, the rollout affects
how surfaces in the NURB S object are displayed
interactively in viewports, including shaded
viewports, and by the preview renderer.
The Viewports surface sett ings are also used when
youapplyameshmodifiersuchasMeshSelectto
the NURBS object. This is important because the
modifier can affect the scene’s geometry.
Render er —When chosen, the rollout affects how
surfaces in the NURBS object are displayed by
the renderer, and by the draft renderer for Quick
Render.
The next cluster of buttons lets you choose which
portions of the geometry are affected by the
surface approximation settings.
Base Surface—Settingsaffecttheentiresurface.
This is the default.
Surf ace Edge—Turn on to set approximation values
fortessellatingsurfaceedgesthataredefinedby
trim curves. With Lock turned off, the sur face and
edge tessellation values are independent of each
other.
For object-level sur faces, this is unavailable unless
Lock (described below) is turned off.
Displaced S ur fa ce—Turn on to set a third,
independent approximation setting for surfaces
that have a displacement map (page 2–1511)
applied to them. Avai lable only when Renderer is
chosen.
Using a preset approximation setting (in the
Presets group box) should give you faster results
for displaced surfaces.
Lock —(for object-level surf aces only) Locks the
BaseSurfacesettingstotheSurfaceEdgesettings.
In other words, surfaces and surface edges have a
relational tessellation setting unless Lo ck is turned
off. Default=on.