Extreme Multi-Resolution Visualization: A Challenge On Many Levels
Authors: Joanna Balme (Space Exploration Technologies Corp.), Eric Brown-Dymkoski (Space Exploration Technologies Corp.), Victor Guerrero (Space Exploration Technologies Corp.), Stephen Jones (Space Exploration Technologies Corp.), Andre Kessler (Space Exploration Technologies Corp.), Adam Lichtl (Space Exploration Technologies Corp.), Kevin Lung (Space Exploration Technologies Corp.), William Moses (Space Exploration Technologies Corp.), Ken Museth (Space Exploration Technologies Corp.), Tom Fogel (NVIDIA Corporation)
Abstract: Accurate simulation of turbulent flows presents significant challenges for both computation and visualization, with length and time scales often spanning 6 orders of magnitude in applied cases. Multi-resolution wavelet analysis is an emerging method for dynamically adaptive simulation, offering compression rates greater than 95% with less than 1% error, however the extreme levels of detail still present challenges for visualization.
These challenges require rendering of multi-resolution data directly in order to avoid an explosion in computation and memory cost. Unfortunately, a wavelet grid is ill-suited to direct visualization. By identifying the opportunity to exploit topological similarities between wavelet grids and octrees, using a multi-resolution data structure known as a VDB-tree, it is possible to adapt the simulation-optimal grid such that it may directly be visualized.
To demonstrate this technique, we set up a series of shear-flow simulations which develop turbulent Kelvin-Helmholtz instabilities. Accurate simulation of these instabilities requires extremely fine resolution, as the smallest scales couple strongly with the large. We show how direct multi-resolution rendering enables visualization pipelines for simulations with between 14 and 17 levels of detail at near-interactive frame rates. This represents a scale-factor of over 100,000 between the smallest and largest structures, with individual frames being generated in less than 1 second.
The use of VDB structures is common in professional and production-quality rendering engines such as Houdini, RenderMan and OptiX, and we show how one of these (OptiX) is enabled by this technique to perform real-time ray tracing on multi-resolution data.
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