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.

This paper presents an efficient algorithm for occlusion culling of urban environments. It is conservative and accurate in finding all significant occlusion. It discretizes the scene into view cells, for which cell-to-object visibility is precomputed, making on-line overhead negligible. Unlike other precomputation methods for view cells, it is able to conservatively compute all forms of occluder interaction for an arbitrary number of occluders. To speed up preprocessing, standard graphics hardware is exploited and occluder occlusion is considered. A walkthrough application running an 8 million polygon model of the city of Vienna on consumer-level hardware illustrates our results.

Visibility determination is a key requirement in a wide range of graphics algorithms. This paper introduces a new approach to the computation of volume visibility, the detection of occluded portions of space as seen from a given region. The method is conservative and classifies regions as occluded only when they are guaranteed to be invisible. It operates on a discrete representation of space and uses the opaque interior of objects as occluders. This choice of occluders facilitates their extension into adjacent opaque regions of space, in essence maximizing their size and impact. Our method efficiently detects and represents the regions of space hidden by such occluders. It is the first one to use the property that occluders can also be extended into empty space provided this space is itself occluded from the viewing volume. This proves extremely effective for computing the occlusion by a set of occluders, effectively realizing occluder fusion. An auxiliary data structure represents oc...

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.

Prioritized-Layered Projection (PLP) is a technique for fast rendering of high depth complexity scenes. It works by estimating the visible polygons of a scene from a given viewpoint incrementally, one primitive at a time. It is not a conservative technique, instead PLP is suitable for the computation of partially correct images for use as part of time-critical rendering systems. From a very high level, PLP amounts to a modification of a simple view-frustum culling algorithm, however, it requires the computation of a special occupancy-based tessellation, and the assignment to each cell of the tessellation a solidity value, which is used to compute a special ordering on how primitives get projected. In this paper, we detail the PLP algorithm, its main components and implementation. We also provide experimental evidence of its performance, including results on two types of spatial tessellation (using octree- and Delaunay-based tessellations), and several datasets. We also discu...

We present a technique for optimizing the rendering of highdepth complexity scenes. Prioritized-Layered Projection (PLP) does this by rendering an estimation of the visible set for each frame. The novelty in our work lies in the fact that we do not explicitly compute visible sets. Instead, our work is based on computing on demand a priority order for the polygons that maximizes the likelihood of rendering visible polygons before occluded ones for any given scene. Given a fixed budget, e.g. time or number of triangles, our rendering algorithm makes sure to render geometry respecting the computed priority. There are two main steps to our technique: (1) an occupancy-based tessellation of space; and (2) a solidity-based traversal algorithm. PLP works by computing an occupancybased tessellation of space, which tends to have smaller cells where there are more geometric primitives, e.g., polygons. In this spatial tessellation, each cell is assigned a solidity value, which is directly proport...

We present an algorithm for visibility preprocessing of urban environments. The algorithm uses a subdivision of line space to analytically calculate a conservative potentially visible set for a given region in the scene. We present a detailed evaluation of our method including a comparison to another recently published visibility preprocessing algorithm. To the best of our knowledge the proposed method is the first algorithm that scales to large scenes and efficiently handles large view cells.

In this paper a novel from-region visibility algorithm is described. Its unique properties allow conducting remote walkthroughs in very large virtual environments, without preprocessing and storing prohibitive amounts of visibility information. The algorithm retains its speed and accuracy even when applied to large viewcells. This allows computing from-region visibility on-line, thus eliminating the need for visibility preprocessing. The algorithm utilizes a geometric transform, representing visibility in a two-dimensional space, the dual ray space. Standard rendering hardware is then used for rapidly performing visibility computation. The algorithm is robust and easy to implement, and can trade off between accuracy and speed. We report results from extensive experiments that were conducted on a virtual environment that accurately depicts 160 square kilometers of the city of London.

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