Parallel direct volume rendering of unstructured grids based on object-space decomposition

Abstract

This work investigates object-space (OS) parallelization of an efficient ray-casting based direct volume rendering algorithm (DVR) for unstructured grids on distributed-memory architectures. The key point for a successful parallelization is to find an OS decomposition which maintains the OS coherency and computational load balance as much as possible. The OS decomposition problem is modeled as a graph partitioning (GP) problem with correct view-dependent node and edge weighting. As the parallel visualizations of the results of parallel engineering simulations are performed on the same machine, OS decomposition, which is necessary for each visualization instance because of the changes in the computational structures of the successive parallel steps, constitutes a typical case of the general remapping problem. A GP-based model is proposed for the solution of the general remapping problem by constructing an augmented remapping graph. The remapping tool RM-MeTiS, developed by modifying and enhancing the original MeTiS package for partitioning the remapping graph, is successfully used in the purposed parallel DVR algorithm. An effective view-dependent cell-clustering scheme is introduced to induce more tractable contracted view-independent remapping graphs for successive visualizations. An efficient estimation scheme with high accuracy is proposed for view-dependent node and edge weighting of the remapping graph. Speedup values as high as 22 are obtained on a Parsytec CC system with 24 processors in the visualization of benchmark volumetric datasets and the proposed DVR algorithm seems to be linearly scalable according to the experimental results.