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There are four menus in the nurbs modeler, plus some common functions:
Next to the nurbs menus there are three groups of functions which you will find in all menus:
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Some Basics
The basic function of the nurbs modeler is to allow the building and animation of
complex surfaces such as human figures, automobile bodies or golf clubs, by
defining simple 3d curves.
Nurbs are "Non-Uniform Rational B-Splines" defined by a mathematical equation that represents a curve as a succession of control segments. This allows users to reshape nurbs objects using control points in a variety of ways. Nurbs is a very powerful modeling tool.
Splines
A spline, in general, is a curve that can be deformed like an elastic strip of wood or metal. In fact, a spline is the mathematical equivalent of an old tool used for the construction of ships: wooden "strips" with attached weights to bend and hold the strip as a smooth shape. There are various types of splines used in computer graphics systems, such as B-Splines, as used in the GIG freeform modeler, or the Catmull-Rom or Hermite splines seen as smooth timecurves in the animation module.
Nurbs can represent a wide variety of curved shapes precisely. For example, ordinary splines in general cannot represent a precise circle. Nurbs, in contrast, can do so. With nurbs, it is therefore possible to represent geometric primitives such as spheres in a simple and general manner.
Nurbs allow flexible control point placement. With a nurbs spline, the "weights" that pulls the "wooden strip" in shape can be placed almost without restrictions along the curve and new weights can be added at any place without changing the shape of the curve. The actual "mass" of the weight can also be changed, in effect pulling the curve closer to the control point, or further away from it.
Nurbs surfaces can also be trimmed. While patches made of ordinary splines generally are rectangular, nurbs surfaces can be cut like a piece of paper.
Swing, Sweep and Ruled
The GIG nurbs modeler makes working with the power of nurbs as easy as possible.
It provides three extremely flexible modeling principles: generalized rotational
bodies, called "swings;" generalized extrusions, called "sweeps;" and a body
defined between 2 curves, called "ruled."
The basic idea is to build complex shapes by defining simple 3d curves. Spatial editing of control points of a 3d-object is seldom, if at all, necessary. 3d surfaces
are reduced to curves that are much easier to grasp.
A "swing" is a shape created by swinging one or more contour curves along a swing curve. For a normal body of revolution, this swing curve would be a circle. The general idea is that the swing curve can be arbitrarily deformed. That is, to create a bathtub for example, you just need to create the bathtub profile and the "top-view" outline of the object.
A "sweep" is made by extruding a contour (multiple contours are also supported) along a given 3d-path which can have an arbitrary shape. Furthermore, it is possible to interpolate between various contour shapes during the process: an object can be defined by a series of cross sections. A boat or the profile of an airplane wing is a typical example. To make the sweeps even more powerful, additional curves are provided that give full control over scaling and twisting of the contour curves. Drill-like or general spiral shapes are thus as simple as straight profile extrusions.
Activating the GIG nurbs Modeler
The nurbs modeler can be activated by selecting nurbs from the tools menu in
the GIG interface.
The nurbs modeler can also be activated by typing in the following command in a
UNIX window after having logged in as GIG:
startNurbs <enter>
