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Surface Approximation 1243
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.
Spatial mesh of t he NURBS teapot
Curvature—(The default.) Generates a variable
tessellation based on the curvature of the surface.
The tessellation has a finer grain where the surface
is more curved. Changing surface curvature
dynamically changes the curvature tessellation.
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. Scaling a surface doesn’t change
its tessellation. Decreasing this value increases
accuracy but increases rendering time. When
you set Distance to 0.0, the software ignores this
parameter 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
softwareignoresthisparameterandusesDistance
to control accuracy.
When b oth Distance and Angle are 0.0, the
surfaces degenerate and can become flat surfaces.
Curvature mesh of the NURBS teapot
Spatial a nd Curvature—Combines the spatial
(edge-length) method and the curvature (dista nce
and ang le) methods, using a ll three va lues.
TheEdgeparameterspecifiesthemaximum
length of a triangular face in t he tessellation. The
valueisapercentageoftheobject’sbounding
box. Decreasing this va lue 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 from the actual
NURBS surface. Distance is a percentage of the
diagonal of each surface’s bounding box. Each
surface in an object is tessellated based on its size,
independently of other surfaces. Scaling a sur face
doesn’t change its tessellation. Decreasing 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 m ax imum ang le
between faces in the approximation. Decreasing
this value increases accuracy but increases
rendering time. When you set Angle to 0 .0, the