Residency Octree: A Hybrid Approach for Scalable Web-Based Multi-Volume Rendering

Lukas Herzberger, Markus Hadwiger, Robert Krüger, Peter Sorger, Hanspeter Pfister, Eduard Gröller, Johanna Beyer

DOI: 10.1109/TVCG.2023.3327193

Room: 103

2023-10-26T23:00:00ZGMT-0600Change your timezone on the schedule page
2023-10-26T23:00:00Z
Exemplar figure, described by caption below
In contrast to octree-based out-of-core approaches (left) which employ a one-to-one mapping between octree nodes and bricks, the residency octree nodes in our approach (right) represent geometric spatial regions, with each node mapping to multiple bricks and vice versa. This decoupling of resolution levels in data set from the spatial subdivision of the tree allows for more fine-grained empty space skipping than previous approaches and makes it possible to directly access any resolution from any node in the residency octree.
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Keywords

Volume rendering, ray-guided rendering, large-scale data, out-of-core rendering, multi-resolution, multi-channel, web-based visualization

Abstract

We present a hybrid multi-volume rendering approach based on a novel Residency Octree that combines the advantages of out-of-core volume rendering using page tables with those of standard octrees. Octree approaches work by performing hierarchical tree traversal. However, in octree volume rendering, tree traversal and the selection of data resolution are intrinsically coupled. This makes fine-grained empty-space skipping costly. Page tables, on the other hand, allow access to any cached brick from any resolution. However, they do not offer a clear and efficient strategy for substituting missing high-resolution data with lower-resolution data. We enable flexible mixed-resolution out-of-core multi-volume rendering by decoupling the cache residency of multi-resolution data from a resolution-independent spatial subdivision determined by the tree. Instead of one-to-one node-to-brick correspondences, each residency octree node is mapped to a set of bricks from different resolution levels. This makes it possible to efficiently and adaptively choose and mix resolutions, adapt sampling rates, and compensate for cache misses. At the same time, residency octrees support fine-grained empty-space skipping, independent of the data subdivision used for caching. Finally, to facilitate collaboration and outreach, and to eliminate local data storage, our implementation is a web-based, pure client-side renderer using WebGPU and WebAssembly. Our method is faster than prior approaches and efficient for many data channels with a flexible and adaptive choice of data resolution.