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1252 Chapter 9: Sur face Modeling
Chang ing surface curvature dynamically changes
the cu rvature tessellation.
The Distance parameter specifies how far the
approximation can deviate from the ac tua l NURBS
surface. Distance is a percentage of the diagonal of
each surface’s bounding b ox. Each surface in an
object is tessellated based on its size, independently
of other surfaces, and scaling a sur face do esn’t
change its tessellation. Decreasing this va lue
increases accuracy but increases rendering time.
When you set Distance to 0.0, the software ignores
this par a meter and uses the Angle 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
softwareignoresthisparameterandusesthe
Distance to control accuracy.
When both Distance and Ang le are 0.0, the
surfaces degenerate and can become flat surfaces.
Curvature mesh of the NURBS teapot
Spatial and Curvature—(The default.) Combines
the spatial (edge-length) method a nd the
cur v ature (distance and angle) methods, using all
three values.
The Edge parameter specifies the maximum
length of a triangular face in the tessellation. The
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 p arameter specifies how far the
approximation can deviate from the actual NURBS
surface. Distance is a percen tage of the diagonal of
each surface’s bounding box. Each surface in an
object is tessellated based on its size, independently
of other surfaces, and scaling a surface doesn’t
change its tessellation. Decreasing this value
increases accuracy but increases rendering t ime.
When you set Distance to 0.0, the software ignores
thisparameterandusestheEdgeandAnglevalues
to control accuracy.
The A ngle p arameter specifies the m ax imum 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, Ang le, and Edge are a ll 0.0, the
surfaces degenerate and can become flat surfaces.
V i ew-Dependent—(for the Renderer only): When
on,takestheobject’sdistancefromthecamera
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 views. This control is
disabled while Viewports is active.
For the Spatial, Curvature, and Spatial and
Curvature methods, when V iew-Dependent is on,
the Distance and Edge values specify pixels instead
of the software’s default units.
Note: When View-Dependent is on, tessellat ion
very quickly reaches the maximum subdivision