High-quality Unstructured Volume Rendering on the PC Platform

For the visualization of volume data the application of transfer functions is used widely. In this area the pre-integration technique allows high quality visualizations and the application of arbitrary transfer functions. For regular grids, this approach leads to a two-dimensional pre-integration table which easily fits into texture memory. In contrast to this, unstructured meshes require a three-dimensional pre-integration table. As a consequence the available texture memory limits the resolution of the pre-integration table and the maximum local derivative of the transfer function. Discontinuity artifacts arise if the resolution of the pre-integration table is too low. This paper presents a novel approach for accurate rendering of unstructured grids using the multi-texturing capabilities of commodity PC graphics hardware. Our approach achieves high quality by reconstructing the colors and opacities of the pre-integration table using the high internal precision of the pixel shader. Since we are using standard 2D multi-texturing we are not limited in the size of the pre-integration table. By combining this approach with a hardware-accelerated calculation of the pre-integration table, we achieve both high quality visualizations and interactive classification updates.