1. If we have a tetrahedral data element with densities at each of the four vertices, how many "cases" are there for polygonal isosurfaces?
2. Suppose we have n3 data elements in a volume. If the densities in the volume are "well behaved," approximately how many cells will contain an isosurface for a particular isovalue?
3. Should we add shadowing to direct volume rendering? Why or why not?