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Surface Approximation Rollout 1251
valueisapercentageoftheobject’sbounding
box. Decreasing this value increases accuracy but
increases rendering time. When you set Edge
to 0.0, the effect is equivalent to the Curvature
method.
The Distance parameter specifies how far the
approximation can deviate f rom the ac tual NURBS
surface. Distance is a percentage of the diagonal of
each sur face’s b ounding box. Each surface in an
object is tessellated based on its size, i ndependently
of other surfaces, and scaling a surface doesn’t
change its tessellation. De creasing this value
increases accuracy but increases rendering time.
When you set Distance to 0.0, the software ignores
this parameter and uses the Edge and Angle values
to control accuracy.
The Angle parameter specifies the maximum angle
between faces in the approximation. Decreasing
this value increases accuracy but increases
rendering time. When you set Angle to 0.0, the
software ignores this parameter and uses the Edge
and Distance values to control accuracy.
When Distance, Angle, and Edge are all 0.0, the
surfaces degenerate and can become flat surfaces.
V i ew-Dependent—(for the Renderer only): When
on, takes the object’s distance from the camera
into account while calculating its tessellation. This
can improve rendering time by not generating
fine-grained tessellations for objects that are
in the distance of the rendered scene. The
view-dependent effect only works when you
render camera or perspective views. It doesn’t
work in orthographic v iews. This control is
disabled while Viewports is active.
For the Spatial, Curvature, and Spatial and
Curvature methods, when View-Dependent is on,
the Distance and Edge values specify pixels instead
of the software’s default units.
Note: When View-Dependent is on, tessellation
very quickly reaches the maximum subdivision
limit. You mig ht want to increase this value to 7
(the greatest va lue allowed). See the descr ipt ion of
Advanced Parameters, below .
Merge—Controls the tessellation of surface
sub-objectswhoseedgesarejoinedorverynearly
joined.Wheninputtoamodifier(suchasMesh
Select)thatrequiresamesh,andwhenNURBS
surfaces are tessellated for production rendering ,
by default the software adjusts the tessellation of
adjoining surfaces to ma tch each other, in terms of
the number of faces along the edges. The Merge
parameter controls how this is done. If Merge is
zero, adjoining faces are unchanged. Increasing
thevalueofMergeincreasesthedistancethe
software uses to calculate how edges should match,
guaranteeing no gaps between the surfaces when
they are rendered. Default=0.01.
In most cases, you don’t need to adjust Merge. If
rendering shows gaps between nearly adjoining
faces, increase Merge to eliminate them.
Technically, the Merge value is one tenth of one
percent of the diagonal of the object ’s bounding
box. In other words, a Merge value of 1.0 (higher
than necessary for most purposes) is 0.1 percent
of the length of the diagonal. Because Merge is
based on the object’s dimensions, you can scale the
NURBS model w ithout affecting the Merge setting.
Advanced Parameters—Click to display the
Advanced Surface Approximation dialog (page
1–1245). The parameters in this dialog apply to
the Spatial, Curvature, and Spatial and Curvature
approxima tion methods.
Cle ar S u rf aces —When on, the settings you choose
in this utility override all sub-object specific
surface approximation settings in the selected
NURBS models. When off, the utility affects
top-level NURBS models but settings local to
individual surface sub-objects remain unaffected.
Default=Off.