We describe an efficient technique for out-of-core construction and accurate view-dependent visualization of very large surface models. The method uses a regular conformal hierarchy of tetrahedra to spatially partition the model. Each tetrahedral cell contains a precomputed simplified version of the original model, represented using cache coherent indexed strips for fast rendering. The representation is constructed during a fine-to-coarse simplification of the surface contained in diamonds (sets of tetrahedral cells sharing their longest edge). The construction preprocess operates out-ofcore and parallelizes nicely. Appropriate boundary constraints are introduced in the simplification to ensure that all conforming selective subdivisions of the tetrahedron hierarchy lead to correctly matching surface patches. For each frame at runtime, the hierarchy is traversed coarse-to-fine to select diamonds of the appropriate resolution given the view parameters. The resulting system can interatively render high quality views of out-of-core models of hundreds of millions of triangles at over 40Hz (or 70M triangles/s) on current commodity graphics platforms.

Recently, several external memory techniques have been developed for a wide variety of graphics and visualization problems, including surface simplification, volume rendering, isosurface generation, ray tracing, surface reconstruction, and so on. This work has had significant impact given that in recent years there has been a rapid increase in the raw size of datasets. Several technological trends are contributing to this, such as the development of high-resolution 3D scanners, and the need to visualize ASCI-size (Accelerated Strategic Computing Initiative) datasets. Another important push for this kind of technology is the growing speed gap between main memory and caches, which penalizes algorithms that do not optimize for coherence of access. Because of these reasons, much research in computer graphics focuses on developing out-of-core (and often cache-friendly) techniques. This paper surveys fundamental issues, current problems, and unresolved questions, and aims to provide graphics researchers and professionals with an effective knowledge of current techniques, as well as the foundation to develop novel techniques on their own. Keywords: Out-of-core algorithms, scientific visualization, computer graphics, interactive rendering, vol-ume rendering, surface simplification.

In this paper we propose three simple, but significant improvements to the OoCS (Out-of-Core Simplification) algorithm of Lindstrom [20] which increase the quality of approximations and extend the applicability of the algorithm to an even larger class of compute systems. The original OoCS algorithm has memory complexity that depends on the size of the output mesh, but no dependency on the size of the input mesh. That is, it can be used to simplify meshes of arbitrarily large size, but the complexity of the output mesh is limited by the amount of memory available. Our first contribution is a version of OoCS that removes the dependency of having enough memory to hold (even) the simplified mesh. With our new algorithm, the whole process is made essentially independent of the available memory on the host computer. Our new technique uses disk instead of main memory, but it is carefully designed to avoid costly random accesses. Our two other contributions improve the quality of the approximations generated by OoCS. We propose a scheme for preserving surface boundaries which does not use connectivity information, and a scheme for constraining the position of the “representative vertex” of a grid cell to an optimal position inside the cell.

We present a novel approach for interactive view-dependent rendering of massive models. Our algorithm combines view-dependent simplification, occlusion culling, and out-of-core rendering. We represent the model as a clustered hierarchy of progressive meshes (CHPM). We use the cluster hierarchy for coarse-grained selective refinement and progressive meshes for fine-grained local refinement. We present an out-of-core algorithm for computation of a CHPM that includes cluster decomposition, hierarchy generation, and simplification. We make use of novel cluster dependencies in the preprocess to generate crack-free, drastic simplifications at runtime. The clusters are used for occlusion culling and out-of-core rendering. We add a frame of latency to the rendering pipeline to fetch newly visible clusters from the disk and to avoid stalls. The CHPM reduces the refinement cost for view-dependent rendering by more than an order of magnitude as compared to a vertex hierarchy. We have implemented our algorithm on a desktop PC. We can render massive CAD, isosurface, and scanned models, consisting of tens or a few hundreds of millions of triangles at 10−35 frames per second with little loss in image quality.

We present a new visibility-based prefetching algorithm for interactive out-of-core rendering of large models on an inexpensive PC. Using an approximate visibility technique, we can very accurately and efficiently determine which geometry will be visible in the near future and prefetch that geometry from disk before it must be rendered. Our prefetching algorithm is a key part of a visualization system capable of rendering a 13-million triangle model with 99% accuracy at interactive frame rates. Our prefetching algorithm is the first of its kind to be based on a from-point visibility technique, and enables interactive rendering on a commodity PC, as opposed to expensive high-end graphics workstations or parallel machines.

We present a novel disk-based multiresolution triangle mesh data structure that supports paging and view-dependent rendering of very large meshes at interactive frame rates from external memory. Our approach, called XFastMesh, is based on a view-dependent mesh simplification framework that represents half-edge collapse operations in a binary hierarchy known as a merge-tree forest. The proposed technique partitions the merge-tree forest into so-called detail blocks, which consist of binary subtrees, that are stored on disk. We present an efficient external memory data structure and file format that stores all detail information of the multiresolution triangulation method using significantly less storage then previously reported approaches. Furthermore, we present a paging algorithm that provides efficient loading and interactive rendering of large meshes from external memory at varying and view-dependent level-of-detail. The presented approach is highly efficient both in terms of space cost and paging performance.

We present iWalk, a system for interactive out-of-core rendering of large models on an inexpensive PC. The system uses a new outof-core preprocessing algorithm and a new multi-threaded out-ofcore rendering approach. The out-of-core preprocessing algorithm is incremental and fast, and it builds an on-disk hierarchical representation for a model larger than main memory. The out-of-core rendering approach uses multiple threads to overlap rendering, visibility computation, and disk operations. A rendering thread uses a from-point visibility algorithm to find the nodes of the model hierarchy that the user sees, and sends fetch requests to a geometry cache, which reads nodes from disk into memory. To avoid bursts of disk operations, a look-ahead thread guesses the nodes that the user may see next, and sends prefetch requests to the geometry cache. The system can run in approximate mode for interactive rendering, or in conservative mode for rendering with guaranteed accuracy. On a commodity PC, iWalk can preprocess a 13-million-polygon model in 17 minutes, and then render it in approximate mode with 98 % accuracy at 9 frames per second. Thus, iWalk allows us to use an inexpensive PC to visualize models that would typically require expensive high-end graphics workstations or parallel machines. 1

In this paper, we present a unified infrastructure for parallel out-ofcore isosurface extraction and volume rendering of large unstructured grids on distributed-memory parallel machines. We parallelize the out-of-core isosurface extraction algorithm of [9] and the out-of-core ZSweep technique [17] for direct volume rendering, using the meta-cell technique as a unified underlying building block.

This paper introduces the 3D Measurement and Virtual Reconstruction of Ancient Lost Worlds of Europe system (3D MURALE). It consists of a set of tools for recording, reconstructing, encoding, visualising and database searching/querying that operate on buildings, building parts, statues, statue parts, pottery, stratigraphy, terrain geometry and texture and material texture. The tools are loosely linked together by a common database on which they all have the facility to store and access data. The paper describes the overall architecture of the 3D MURALE system and then briefly describes the functionality of the tools provided by the project. The paper compares the multimedia studio architecture adopted in this project with other multimedia studio architectures.

This paper presents a novel algorithm combining view-dependent rendering and conservative occlusion culling for interactive display of complex environments. A vertex hierarchy of the entire scene is decomposed into a cluster hierarchy through a novel clustering and partitioning algorithm. The cluster hierarchy is then used for view-frustum and occlusion culling. Using hardware accelerated occlusion queries and frame-to-frame coherence, a potentially visible set of clusters is computed. An active vertex front and face list is computed from the visible clusters and rendered using vertex arrays. The integrated algorithm has been implemented on a Pentium IV PC with a NVIDIA GeForce 4 graphics card and applied in two complex environments composed of millions of triangles. The resulting system can render these environments at interactive rates with little loss in image quality and minimal popping artifacts. Keywords: Interactive Display, View-Dependent Rendering, Occlusion Culling, Level of Detail, Multiresolution Hierarchies 1