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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
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.
Mon Mar 30 11:23:18 MES 1998