Fast out-of-core isosurface extraction and rendering of time-varying data sets

We present a combination of techniques for interactive out-of-core isosurface extraction and rendering of time-dependent data sets. We make use of an index tree that allows extraction of all isovalue-spanning cells from any time step, and for any isovalue, at rates of several hundreds of frames per second. This data structure is constructed in a pre-processing stage, and effectively uses the temporal coherence in the data set. However, for very large data sets such as those resulting from CFD simulations, this tree structure can easily become too large to fit in main memory. Therefore, we have adapted the data structure for out-of-core application by adding an intelligent paging scheme, which allows interactive exploration of very large data sets on a normal PC. Only a userspecified time window will be kept in main memory and other parts of the tree will be read and released on-demand. This paging scheme was implemented using multi-threading. Finally, to avoid timeconsuming triangulation and surface reconstruction, we have used a hardware-assisted direct point rendering algorithm, achieving interactive rendering frame rates.