Looking at Daniel Chin's message, I realize that I forgot to
provide any performance info on VolPack. Here is some, for
a 256x256x84 bytes volume of an MRI head: times are in seconds for
one rendering, with different pre-processings of the volume
(none/ simple/ full)
        sgi r3000/ irix-4.0.5: 3.2/  .7/  .3
        sgi r4000/ irix-5.2:   2.3/  .5/  .3
        dec 5000/ ultrix-4.2: 10.3/ 1.8/  .9
        sparc1+/ sunos4.1.2:  18.3/ 2.9/ 2.2
        sparc20/ sunos4.1.3:   2.5/  .6/  .3
 
(note 1: it would be interesting to know performances on a fast, cheap NT box
or on a PowerMac; has anyone installed VolPack on these platforms ?)
(note 2: a parallel version of the algorithm can render at video rates
on an sgi MP challenge server)
 
On my r3000 system, with 256^3 volumes, I experience timings of
6 to 20 seconds per frame for complex scenes. This can be slightly
slower than VoxelView on a VGX, but then the lights & materials settings
are much more elaborate, and so the image quality-information content
is better.
 
One must realize that such speed comes at the cost of:
        1) an optional volume pre-processing time
        (pre-processing time being a fixed cost, one uses it only
        when a large number of frames will be needed with the same
        voxels/edges classification, usually more than 30 or 60)
        2) a larger than usual use of RAM, but is not RAM cheaper
        than software and graphics pipelines?
 
Correction: VolPack is by Philippe Lacroute and Marc Levoy.
 
 
  --Jean-Pierre