Visibility algorithms for walkthrough and related applications have grown into a significant area, spurred by the growth in the complexity of models and the need for highly interactive ways of navigating them. In this survey, we review the fundamental issues in visibility and conduct an overview of the visibility culling techniques developed in the last decade. The taxonomy we use distinguishes between point-based and from-region methods. Point-based methods are further subdivided into object and image-precision techniques, while from-region approaches can take advantage of the cell-and-portal structure of architectural environments or handle generic scenes.

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We propose a novel conservative visibility culling technique based on the Prioritized-Layered Projection (PLP) algorithm. PLP is a time-critical rendering technique that computes, for a given viewpoint, a partially correct image by rendering only a subset of the geometric primitives, those that PLP determines to be mostly likely visible. Our new algorithm builds on PLP and provides an efficient way of finding the remaining visible primitives. We do this by adding a second phase to PLP which uses image-space techniques for determining the visibility status of the remaining geometry. Another contribution of our work is to show how to efficiently implement such image-space visibility queries using currently available OpenGL hardware and extensions. We report on the implementation of our techniques on several graphics architectures, analyze their complexity, and discuss a possible hardware extension that has the potential to further increase performance. CR Categories: I.3.3 [Computer Gra...

this paper, we present an algorithm for general visibility queries. This algorithm exploits several OpenGL features in order to obtain faster results for large polygonal models. To show the applicability of our algorithm -- in terms of graphics performance -- on low-end graphics workstations, we performed all measurements on an SGI O2 /R10000 and an SGI Octane/MXE graphics workstation. Furthermore, we propose an extension to the OpenGL rendering pipeline to add features for improved general occlusion culling.

Figure 1: Magic volume lens results. (a) magnifying inside features in an arbitrary-shaped area on an engine, (b) applying sampling-rate-based lens on a foot, (c) enlarging area of interest on an aneurism, (d) magnifying the duodenum of a segmented frog dataset. The size and resolution of volume datasets in science and medicine are increasing at a rate much greater than the resolution of the screens used to view them. This limits the amount of data that can be viewed simultaneously, potentially leading to a loss of overall context of the data when the user views or zooms into a particular area of interest. We propose a focus+context framework that uses various standard and advanced magnification lens rendering techniques to magnify the features of interest, while compressing the remaining volume regions without clipping them away completely. Some of these lenses can be interactively configured by the user to specify the desired magnification patterns, while others are featureadaptive. All our lenses are accelerated on the GPU. They allow the user to interactively manage the available screen area, dedicating more area to the more resolution-important features.

The paper goal is to fit trilinear iso-surfaces out of volume data, by adopting an adaptive mesh refinement approach and therefore supporting a higher accuracy with respect to standard MC solutions. In order to be correct, adaptive refinement must be applied to a topologically correct initial mesh patch. For this reason, we designed a new, Exhaustive Look Up Table (ELUT) which encodes multi-entry patterns for each ambiguous configuration. Following the solution proposed by Natarajan, for each ambiguous configuration we choose, at run time, the actual pattern by evaluating the corresponding set of saddle points. Once the corresponding starting patch has been read from the ELUT, it is adaptively refined to fulfill a user-selected accuracy. Refinement is adaptive to ensure that the complexity of the fitted mesh will not become excessive. An evaluation of the results produced on some volume dataset is reported, both in terms of accuracy and complexity of the meshes obtained. Contact autho...

Visualizing very large volume data has been recognized as a task requiring great effort in a variety of science and engineering fields. In particular, such data usually places considerable demands on run-time memory space. This paper describes an effective 3D compression scheme for very large volume data that exploits the power of wavelet theory. In designing our compression method, we have compromised between two important factors: high compression ratio and fast run-time random access. Our experimental results on the Visual Human data sets show that our method achieves fairly good compression ratios. In addition, it minimizes the overhead caused during run-time reconstruction of voxel values. This 3D compression scheme will be useful in developing many interactive visualization systems for huge volume data, and will make visualization technology accessible to a much wider range of users, as it can be based on personal computers or low-end workstations with limited memory. Keywords: ...

Interactive visualization of very large volume data has been recognized as a task requiring great effort in a variety of science and engineering fields. In particular, such data usually places considerable demands on run-time memory space. In this paper, we present an effective 3D compression scheme for interactive visualization of very large volume data, that exploits the power of wavelet theory. In designing our method, we have compromised between two important factors: high compression ratio and fast run-time random access ability. Our experimental results on the Visual Human data sets show that our method achieves fairly good compression ratios. In addition, it minimizes the overhead caused during run-time reconstruction of voxel values. This 3D compression scheme will be useful in developing many interactive visualization systems for huge volume data, especially when they are based on personal computers or workstations with limited memory. Keywords: very large volume data, wavele...

For interactive rendering of large polygonal objects, fast visibility queries are necessary to quickly decide whether polygonal objects are visible and need to be rendered. None of the numerous published algorithms provide visibility performance for interactive rendering of large models. In this paper, we propose an OpenGL extension for fast occlusion queries. Added after the depth test stage of the OpenGL rendering pipeline, our algorithm provides fast queries to establish the occlusion of polygonal objects. Furthermore, hardware aspects of this proposal are discussed and possible implementations on two different graphics architectures are presented.

. Virtual Medicine is an emerging and challenging field in Computer Graphics. Numerous visualization methods are used to model and render data of different modalities. In this paper, we present a new endoscopy system for virtual medicine. The main purpose of this system is to provide support for the planning of complicated endoscopic interventions inside of the ventricular system of the human brain. Although, our current focus is on ventricle endoscopy, this system is applicable to other areas as well. In order to achieve interactive framerates on workstations with medium graphics performance, we apply an efficient implementation of a basic algorithm for general visibility queries. Keywords: Virtual Medicine, Virtual Environments, Surgical Assist Systems. 1 Introduction Minimally-invasive neurosurgical procedures are of increasing importance in neurosurgery. In comparison to commonly used surgical techniques, less brain tissue is damaged. Furthermore, minimally-invasive pr...