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NURBS, which is an acronym for Non-Uniform Rational B-Spline, is a
computer method for constructing smooth, freeform curves and surfaces.
Most of today's 3D modeling programs rely on NURBS for constructing
surface models, and sometimes even for solid models. Here are the reasons
for its widespread use.
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NURBS can construct a wide
range of geometric shapes, ranging from simple straight lines to
complex, but perfectly smooth, sculpted surfaces.
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NURBS efficiently creates
complex shapes, with a minimum amount of data and relatively few
calculations.
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NURBS has a precise and almost
universally recognized definition, which makes it easy to transfer
geometry between CAD programs.
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Objects based on NURBS can be
edited at a basic level
NURBS was developed to
construct digital versions of the drafting splines once used to draw
cross-sections of ship hulls and airplane fuselages. These splines were
flexible strips of plastic, metal, or wood that could be bent to form
smooth curves; weights were attached to them to maintain their shape.
Curves made by splines are unique in that the curvature (and, hence, curve
radius) continually changes along their length. Curves made up of arcs, on
the other hand, have discrete points at which the curve radius
changes-even if the arcs are tangent to one another and the curve has a
smooth appearance.
NURBS objects not only emulate drafting splines but also create 3D splines
that twist and turn through space, as well as surfaces having spline-like
properties. Control points, which are analogous to the weights used with
drafting splines, establish the shape of a NURBS curve. Except for the
endpoints of a curve (or endpoint, if it is a closed curve), these control
points are away from the curve. They act as magnets, pulling the curve
toward themselves, and when you move a control point the curve changes its
shape to accommodate the new control point location. Normally control
points are not visible, but most programs allow you to temporarily display
them so that you can move them or modify them.
NURBS is the best 3-D modeling technology for designers. They can
capture and refine ideas and accurately communicate them through every
step to manufacturing. With NURBS, designers can model any shape from a
simple 2-D arc to the most complex 3-D organic free-form surface, or
solid. Because of their accuracy, NURBS can be used in any process from
drafting, illustration, and animation to analysis and manufacturing.
Since NURBS is proven technology, it is used by most design, drafting,
CAM, engineering, prototyping, analysis, rendering, animation, and
illustration software.
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