Tobias's VoRANG Page

Direct Volume Rendering is a very powerful method for visualizing 3D scalar fields. In volume rendering data distributions are depicted as semitransparent colored clouds. With this visualization method the user can gain an overview insight into complex data distributions from one picture alone.

In the course of my graduate studies and my work at ZIB in Berlin I developed an extensive framework for doing volume rendering on unstructured (tetrahedral) grids. Data fields defined on such irregular meshes often appear as intermediate or final results of numerical simulations employing finite element methods.

The production of meaningful volume rendering pictures relies heavily on successfully managing many different rendering parameters. Most importantly, adequate color and transparency transfer functions have to be found but other settings (viewing parameters, inclusion of 3D clues, external illumination, degree of approximation) are also important.

The abovementioned system, called VoRANG (Volume Rendering auf Nichtregulären Gittern, or in English, Volume Rendering on Nonregular Grids), offers a flexible framework for testing and evaluating different strategies for finding the best settings for a given data set. VoRANG's object oriented code is quite portable since I did not make use of any graphics libraries but instead built the whole graphics pipeline on my own.

Below you can find some images that have been produced using VoRANG:

Gallery

This is the very first test example that I used: A box consisting of 12 tetrahedra of the same shape with a different color defined at each node. For the visualization, I assumed uniform transparency and linear interpolation of color.

Here you can see the box spinning in a mpeg movie.
This is the rendering of a later sample dataset: three overlapping gaussian curves. Though you can see the underlying tetrahedral grid, no sampling of the test function has taken place here. The renderer used the mathematically correct function which was plugged into the system as a customized interpolation routine - an example of the flexibility of VoRANG as a testing environment.
The famous teapot. Volume rendering reveals that there really is a teabag in there !
When I first learned about computer graphics and played around with the polygonal and Bezier models of the Utah teapot, I was pretty disappointed that whenever I tried to look inside there was absolutely nothing, just pure void, not even inner walls! (Well, how did you learn about backface culling ?)
Finally, this is a rendering for a medical application: You see a temperature distribution in the pelvic region during a simulated treatment of Hyperthermia (a cancer fighting therapy where you try to destroy the tumor by overheating it).
The tumor (at the prostate gland) is centered in this picture. It indeed receives the highest temperature (as depicted by the highest opacity and brightest color).

htobias@cs.columbia.edu

	This is the very first test example that I used: A box consisting of 12 tetrahedra of the same shape with a different color defined at each node. For the visualization, I assumed uniform transparency and linear interpolation of color. Here you can see the box spinning in a mpeg movie.
	This is the rendering of a later sample dataset: three overlapping gaussian curves. Though you can see the underlying tetrahedral grid, no sampling of the test function has taken place here. The renderer used the mathematically correct function which was plugged into the system as a customized interpolation routine - an example of the flexibility of VoRANG as a testing environment.
	The famous teapot. Volume rendering reveals that there really is a teabag in there ! When I first learned about computer graphics and played around with the polygonal and Bezier models of the Utah teapot, I was pretty disappointed that whenever I tried to look inside there was absolutely nothing, just pure void, not even inner walls! (Well, how did you learn about backface culling ?)
	Finally, this is a rendering for a medical application: You see a temperature distribution in the pelvic region during a simulated treatment of Hyperthermia (a cancer fighting therapy where you try to destroy the tumor by overheating it). The tumor (at the prostate gland) is centered in this picture. It indeed receives the highest temperature (as depicted by the highest opacity and brightest color).