'nurs' [<name(char9)>|'!' ['DEFINE' ['COMPACT'] ->
<u.deg> <v.deg> <u.npnt> <v.npnt> <u.nknt> <v.nknt>]|
['CONTROL' <u.index> <v.index> [<pnt>|<x y z>] ->
['KNOT' <U>|<V> <index> <value>]|
[ <!> <setname(containing surfaces)>]
This keyword is used to define a nurbs shape. Surfaces might use nurbs to define the interior geometry. There are two possible ways of definition. The first is using predefined point names and the second is by specifying the coordinates explicitly. When the coordinates are defined, then the parameter ''COMPACT'' must be used as shown above but when point names are used, then ''COMPACT'' must be omitted. CAD-interfaces might use this functionality.
REMARK: The knot-vector has to have a multiplicity of ``degree+1''.
There is also a small nurbs-building capability in cgx. It is possible to use existing surfaces (with 4 edges) which do not already reference a given nurbs. The new nurbs will follow the Coons-algorithm but can be modified by moving the control points. The surfaces must be stored in a set. For example,
nurs ! surfaceSet
will define nurbs for all surfaces stored in the set surfaceSet. This nurbs can be used to define the interiour of other surfaces. This is necessary if ``tr3u'' elements (unstructured triangles) should be used and if the surface is not related to a given shape.