SI_NurbsSurface

SI_NurbsSurface

Defines a NURBS surface.

This template provides a definition for existing NURBS representations, such as IGES. This ensures that the SI_NurbsSurface representation is compatible with most existing game engines and file formats.

SI_NurbsSurface always stores surface data in IGES format.

This template corresponds to the CSLNurbsSurface class.

Limitation

Note that if you export a NURBS surface from Softimage that has a different U and V parameterization, the dotXSI file format can only support a single parametrization in both U and V.

Introduced

1.3

Members

Member name	Type	Array size	Description
uvDegree	array int	2	Degree of surface in U and V.
uvClosed	array BOOLEAN	2	Surface is closed in U.
paramType	int		Knot parameterization of the NURBS curves: 0 = uniform 1 = open uniform 2 = non-uniform 3 = chord length 4 = centripetal
nbUVKnots	array int	2	Number of IGES knots in U and V.
uKnots	array DOUBLE	nbUKnots	Knots in U.
vKnots	array DOUBLE	nbVKnots	Knots in V.
nbControlPoints	array int	3	Total number of IGES control points: • Number of control points in U • Number of control points in V
controlPoints	array vector	nbControlPoints[0]	Surface control points: x, y, z, w

Nested Templates

SI_Material

SI_Texture2D

SI_SubelementUserDataVertex_<userDataTag>

SI_ShapeAnimation (v2.0 only)

Comments

Closed in U or V implies that a surface is periodic (its continuity is degree –1 by formulation and not construction). In IGES format it implies an overlapping of degree control points, not just the last and first ones.

The IGES Nurbs representation implies:

Open curves have an extra order knot at the end and at the start (order = degree + 1).

Closed (periodic) curves have knot spacing overlap and an overlapping of degree control points.

The SI|3D NURBS representation implies:

• Open curves have an extra degree knot at both the end and start, with the number of control points given by:

   nbControlPoints = nbKnots - (degree + 1)

• Closed curves have no overlap:

   nbControlPoints = nbKnots - 1

The following table summarizes how the number of IGES control points and IGES knots are calculated.

Constant name	Open	Closed
nbSoftKnots	nbSoftPoints + degree - 1	nbSoftPoints + 1
nbIgesPoints	nbSoftPoints	nbSoftPoints + degree
nbIgesKnots	nbSoftKnots	nbSoftKnots + 2*degree

nbSoftPoints is the number of control points in U (or V) for a NURBS surface in SI|3D. This is the number shown in the NURBS Surface Info dialog box.

nbSoftKnots is the number of knots in U (or V) for a NURBS surface in SI|3D.

nbIgesPoints and nbIgesKnots are the numbers of U (or V) points and knots output in a dotXSI file.

Example

SI_NurbsSurface grid3 {
   1; 1;; // Linear in U, V 
   1; 0;; // Closed in U, Open in V 
   0;  // Uniform parameterization 
   6; 3;; // 6 knots in U, 3 knots in V 
   0.000000; 0.000000; 1.000000; 2.000000; 3.000000; 3.000000; ;
   0.000000; 1.000000; 2.000000; ;
   12; 4; 3;; // Number of control points: Total, U, V
// Control points: 
   -1.000000;0.000000;1.000000;1.000000;,
   0.000000;0.000000;1.000000;1.000000;,
   1.000000;0.000000;1.000000;1.000000;,
   -1.000000;0.000000;1.000000;1.000000;,
   -1.000000;0.000000;0.000000;1.000000;,
   0.000000;0.000000;0.000000;1.000000;,
   1.000000;0.000000;0.000000;1.000000;,
   -1.000000;0.000000;0.000000;1.000000;,
   -1.000000;0.000000;-1.000000;1.000000;,
   0.000000;0.000000;-1.000000;1.000000;,
   1.000000;0.000000;-1.000000;1.000000;,
   -1.000000;0.000000;-1.000000;1.000000;;

   SI_Material {
       ...
       SI_Texture2D {
          ...
       }
   }
}