Implementation

The flexible framework for volume tracing has been implemented as a part of the ``Advanced Rendering Toolkit'' (ART for short), which is being developed at the Institute of Computer Graphics in Vienna. ART is a set of Objective C Libraries that provide a wide range of functionality suitable for graphics applications. The ART libraries do not deal with the user interface, they provide classes and methods starting with primitive graphics objects like vectors, points and matrices up to classes that make it possible to define complete three dimensional scenes and a number of different methods to manipulate and render these scenes.

Figure 2: Absorption, Scattering and Shaded Scattering: a cloud, composed out of noise, tubulence and a spherical density emitter is shown. The left cloud only absorbs light, which results in a black-smoke-like appearance. The second cloud has been rendered using absorption and scattering, yielding a more natural appearance. Finally, in the right image, shaded scattering has been used.

Figure 3: Volume Data Sets (kidneys, section of a human head, Courtesy VisMed-Project): the left image has been rendered using trilinear interpolation, as a result, no distinct voxels can be seen. The second image showns the same data-set using Levoys isosurface algorithm. The third image has been rendered using shaded scattering.

Figure 4: Natural Phenomena: Two candlelights, one quite turbulent flame and some smoke rising from a burned match. Although both the candlelights and the flame are rendered using emission, these media do not act as light sources, which results in a somewhat unrealistic lighting of the scene.