Volume Visualization

Level Surfaces on Scalar Fields

[image of SCIPUFF smoke plume] [image of TASS simulation of Ivy King nuclear cloud] [image of Neanderthal skull] [image of YIQ color cube] Unlike a lot of 3D artists who start out with a desire to remake Star Wars, I got into 3D by visualizing clouds and smoke plumes. The methods I used were originally created for 3D medical imaging data, but they can be applied to any 3D array of density values. Left to right: SCIPUFF smoke plume; TASS simulation of the Ivy King nuclear test; Neanderthal skull found in 1908 near La Chapelle-aux-Saints, France; NTSC color in RGB space.

TASS (Terminal Area Simulation System) was written for NASA by Fred Proctor in 1987 to study mesoscale weather events like thunderstorms and microbursts, but it was also run on the Cray YMP at Los Alamos to study the atmospheric effects of nuclear blasts. To validate it for this purpose, it was used to simulate actual tests, including the November 1952 Ivy King shot, a 500 kiloton airburst over Enewetak Atoll in the Pacific.

I was a freelance computer artist creating viewgraphs for a Defense Department contractor in 1990 when I first encountered the Ivy King simulation. The TASS output had been visualized as a wireframe plot, and I was asked to digitally paint over the wireframe to make it look more like a cloud. I did that, but I was sure there was a better way, so I gave myself a crash course in 3D graphics, and six months later I was awarded an SBIR for nuclear cloud visualization.

SCIPUFF, developed by Ian Sykes, is an atmospheric transport modeler that simulates the dispersion of airborne material (smoke, chemicals, biological agents). It models a plume as a set of Lagrangian puffs, which can be thought of as ellipsoidal density emitters. You can visualize the ellipsoids directly, but you can also sample the density onto a scalar field and visualize it like the TASS output.

NTSC is the analog television signal format used for decades in the United States, now replaced by the digital ATSC format, which includes the high definition standard. Mathematically, the conversion from RGB color to NTSC's YIQ is a simple linear transformation (a 3 x 3 matrix) that's lossless and invertible. In practice, though, there are some RGB colors, described as hot, that can't be encoded in NTSC, particularly fully saturated yellow and cyan and, to a lesser extent, red and green. The part of the RGB cube that fits into NTSC can be visualized as a level surface on a scalar field.

The raw data for the CT scan of the La Chapelle fossil can be downloaded from the FOVEA Project site. FOVEA is a French effort to study and promote the use of 3D graphics in paleoanthropology. Another source of 3D hominid fossil data and information is the University of Vienna's Virtual Anthropology site, where you can get CD-ROMs containing data for half a dozen fossil hominids. I used the FOVEA La Chapelle data in November 2004 to create the model shown here.