A Survey of Volumetric Illumination Techniques for Interactive Volume Rendering <s> Future Challenges <s> We present a new parallel multiresolution volume rendering framework for large-scale time-varying data visualization using the wavelet-based time-space partitioning (WTSP) tree. Utilizing the wavelet transform, a large-scale time-varying data set is converted into a space-time multiresolution data hierarchy, and is stored in a time-space partitioning (TSP) tree. To eliminate the parent-child data dependency for reconstruction and achieve load-balanced rendering, we design an algorithm to partition the WTSP tree and distribute the wavelet-compressed data along hierarchical space-filling curves with error-guided bucketization. At run time, the WTSP tree is traversed according to the user-specified time step and tolerances of both spatial and temporal errors. Data blocks of different spatio-temporal resolutions are reconstructed and rendered to compose the final image in parallel. We demonstrate that our algorithm can reduce the run-time communication cost to a minimum and ensure a well-balanced workload among processors when visualizing gigabytes of time-varying data on a PC cluster. <s> BIB001 </s> A Survey of Volumetric Illumination Techniques for Interactive Volume Rendering <s> Future Challenges <s> We present a direct interblock interpolation technique that enables direct volume rendering of blocked, multiresolution volumes. The proposed method smoothly interpolates between blocks of arbitrary block-wise level-of-detail (LOD) without sample replication or padding. This permits extreme changes in resolution across block boundaries and removes the interblock dependency for the LOD creation process. In addition the full data reduction from the LOD selection can be maintained throughout the rendering pipeline. Our rendering pipeline employs a flat block subdivision followed by a transfer function based adaptive LOD scheme. We demonstrate the effectiveness of our method by rendering volumes of the order of gigabytes using consumer graphics cards on desktop PC systems. <s> BIB002
Though the techniques presented in this article allow realistic volume rendered images to be generated at interactive frame rates, still several challenges exist to be addressed in future work. When reviewing existing techniques it can be noticed that, although the underlying optical models already contain simplifications, there is sometimes a gap between the model and the actual implementation. In the future it is necessary to narrow this gap by providing physically more accurate illumination models. Apart from that, large data sets still pose a driving challenge. Here, the illumination computation time increases and it is not possible to store large intermediate data sets due to memory limitations. Although memory capacity on GPUs has increased during the last couple of years, the speed at which data can be transferred for calculations has not increased at the same rate. Multiresolution data structures BIB001 BIB002 and explicit caches [JGY * 12] could alleviate these problems but more work in relation to volumetric illumination is needed.