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VRML Scene graph

The VRML scene graph stores all the different levels of detail of the iso-surface (Fig. 2). In order to switch between the different levels a Switch node is used as the root node for the scene graph. Each child of this switch node is a Group node, that represents one level of the iso-surface. The children of a Group node are Shape nodes, which consist of an Appearance and a Geometry node. We use IndexedFaceSet nodes as Geometry nodes.

 
Figure 2:  VRML Scene graph for the iso-surface hierarchy

Each level of the iso-surface contains two types of triangles: regular and irregular ones as described in Section 3. Figs. 3(b,c) show the regular triangles for two different levels of an iso-surface while Figs. 3(e,f) show the corresponding irregular triangles. The complete iso-surfaces can be seen in Figs. 3(a,d). Regular triangles will not change in the higher levels of the surface. Regular triangles of level m are reused in all levels . Irregular triangles are replaced in the higher levels of the iso-surface. Irregular triangles of level m are only used at level m.

       
Figure 3:  Isosurface of a spherical harmonic function

We remark, that the first levels of an iso-surface may be empty. If triangle data is received, VRML geometry must be created dynamically. For this purpose the two different approaches, introduced in Section 4.2 were implemented. The details of these approaches are described in the following two subsections.

• Parser generated Nodes
• Data Events