Create NURBS Net

The Effect->CreateNURBSNet command in the Model module generates QTMs (quadratic texture maps). This command is a necessary step before exporting models for certain games platforms.

A QTM is a quadratic NURBS surface with an associated texture. They can be drawn with parametric surface hardware accelerators.

This effect can be run either on polygon meshes with triangular or quadrilateral faces, or on quadratic NURBS surfaces. It is optimized for models generated by the Effect->Web command. Use polygon meshes if you want to keep a high level of detail. If you want to eliminate detail to speed up rendering, use NURBS surfaces.

When the effect converts a polygon mesh, it creates a separate QTM for each face. Similarly, when the effect converts a quadratic NURBS surface, it creates a separate QTM for each area of the surface bounded by control points. In both cases, the network of QTMs is grouped in a hierarchy under a null object. The original model is not destroyed.

Procedure

1. Create a polygon mesh with triangular or quadrilateral faces, or a quadratic NURBS surface.
2. For a polygon mesh object, bind the textures to the model's uv coordinates using the Txt_Oper->Info UV Coord. (2D Global) command in the Matter module.
3. Choose the Effect->CreateNURBSNet command in the Model module. The Create NURBS Net dialogue box is displayed.
4. Set the parameters as desired and click Ok.
5. Pick the model. A network of QTMs is generated.
6. If desired, you can optimize the generated textures further. To do this, select them in the Schematic window and choose the Mat_Oper->Optimize Selected command in the Matter module.

Parameters

Smooth Edges

This option smooths edges below the specified dihedral angle. It is applicable only to polygon mesh objects. If the dihedral angle of an edge is less than the value specified here, the effect creates QTMs that join smoothly.

The dihedral angle of an edge is the angle between the normals of its adjacent faces. Dihedral angles range in value between zero and 180 degrees. Edges in flat areas have small dihedral angles, and edges in sharp areas have large dihedral angles.

Resample Textures

This option creates a new texture for each QTM. Textures are resampled at the value specified in texture elements (texels) per SOFTIMAGE unit. The default is 20. Use higher values to keep more detail, and lower values to eliminate more detail.

Textures are created in the current directory. However, you are prompted to move them to the PICTURES directory when you save the scene. If you are not running SOFTIMAGE 3D from your home directory, make sure that you have write permission for the current directory; otherwise, textures cannot be generated.

Export QTM Network

This option exports the structure of the resulting QTM network to an ASCII file. This allows you to write your own routines for manipulating them or importing them to other formats. The ASCII file consists of three lists:

• A list of control points.
• A list of normals.
• A list of QTMs, referencing the lists of control points and normals.

Type a file name for the ASCII file in the text box provided, or click the Browser button to select a directory and file name.

Last updated 02-apr-1998