Issue 2

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https://diglib.eg.org/handle/10.2312/95

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    Automatic Camera Placement for Image-Based Modeling
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Fleishman, Shachar; Cohen-Or, Daniel; Lischinski, Dani
    We present an automatic camera placement method for generating image-based models from scenes with known geometry. Our method first approximately determines the set of surfaces visible from a given viewing area and then selects a small set of appropriate camera positions to sample the scene from. We define a quality measure for a surface as seen, or covered, from the given viewing area. Along with each camera position, we store the set of surfaces which are best covered by this camera. Next, one reference view is generated from each camera position by rendering the scene. Pixels in each reference view that do not belong to the selected set of polygons are masked out.The image-based model generated by our method, covers every visible surface only once, associating it with a camera position from which it is covered with quality that exceeds a user-specified quality threshold. The result is a compact non-redundant image-based model with controlled quality.The problem of covering every visible surface with a minimum number of cameras (guards) can be regarded as an extension to the well-known Art Gallery Problem. However, since the 3D polygonal model is textured, the camera-polygon visibility relation is not binary; instead, it has a weight - the quality of the polygon's coverage.
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    Book Reviews
    (Blackwell Publishers Ltd and the Eurographics Association, 2000)
    Books reviwed:F. S. Hill Jr, Computer Graphics using OpenGL (Second edition)Barry Blundell, and Adam Schwarz, Volumetric Three Dimensional Display SystemsEdward Angel, Interactive Computer Graphics: A Top-Down approach with OpenGL (Second Edition)J.-R Sack, and J. Urrutia, (eds) Handbook of Computational GeometryTomas Moller, and Eric Haines, Real-Time Rendering
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    Carla Vandoni - A Remarkable Lady
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Duce, David
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    Computation of Irradiance from Triangles by Adaptive Sampling
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Urena, C.
    We introduce an algorithm for sample positioning in a planar triangle, which can be used to make numerical integration of an arbitrary function defined on it. This algorithm has some interesting properties which make it suitable for applications in the context of realistic rendering. We use an adaptive triangle partitioning procedure, driven by an appropriate measure of the error. The underlying variance is shown to be bounded, and in fact it can be controlled, so that it approaches the minimum possible value. We show results obtained when applying the method to irradiance computation, in the context of final-gather algorithms. We also describe a C++ class which offers all required functionality, and we made available its source code.
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    Conflict Neutralization on Binary Space Partitioning
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) James, A.; Day, A.M.
    The Binary Space Partitioning (BSP) tree achieves fast hidden surface removal for most practical applications where an observer can move through a scene of static objects. However, the BSP algorithm generally increases the number of polygons in a scene due to its splitting stage resulting in a detrimental effect on the priority ordering and more significantly, the display calculations (shading, lighting, shadows, etc.) of the rendering pipeline.We present the Conflict Neutralization algorithm which attempts to reduce the number of splits more effectively than existing techniques whilst maintaining the 'standard' model of a BSP tree. Our idea is similar to Conflict Minimization proposed by Fuchs; the significant difference is that our algorithm recognizes that a polygon suitable for selection in the Minimization criterion may subsequently stop the remainder of polygons achieving some reductions in cuts-with Conflict Neutralization, such a polygon is demoted.We compare the results of Conflict Neutralization against Conflict Minimization, the Least-crossed with Most-crossed tie-breaking criterion and our own, enhanced implementation of Conflict Minimization. We show how these techniques fall into different 'depths of analysis'.
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    Dynamic Polygon Visibility Ordering for Head-Slaved Viewing in Virtual Environments
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Sadagic, Amela; Slater, Mel
    This paper presents an approach to visibility called the Viewpoint Movement Space (VpMS) algorithm which supports the concept of dynamic polygon visibility orderings for head-slaved viewing in virtual environments (VE). The central idea of the approach is that the visibility, in terms of back-to-front polygon visibility ordering, does not change dramatically as the viewpoint moves. Moreover, it is possible to construct a partition of the space into cells, where for each cell the ordering is invariant. As the viewpoint moves across a cell boundary typically only a small and predictable change is made to the visibility ordering. The cost to perform this operation represents a notable reduction when compared with the cost of resolving the visibility information from the BSP tree where the classification of the viewpoint with every node plane has to be performed. The paper demonstrates how the subdivision into such cells can represent the basic source for an acceleration of the rendering process. We also discuss how the same supportive data structure can be exploited to solve other tasks in the graphics pipeline.
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    Editorial
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Coquillart, Sabine; Duke, David
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    Eurographics
    (Blackwell Publishers Ltd and the Eurographics Association, 2000)
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    Hierarchical Reconstruction of BRDFs using Locally Supported Functions
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Noe, N.; Peroche, B.
    BRDFs are the backbone of realistic rendering algorithms. Analytical models are sometimes ineffective since they frequently cannot represent very particular material characteristics (retro-reflection, anisotropy, off-specularity, .). Consequently one might want to use measured BRDF data directly; this leads to solving the problem of BRDF reconstruction. In this paper, we propose a new solution which uses locally supported functions that lead to a hierarchical approach able to take irregular distributions of sampled data into account. This method is not computationally expensive and guarantees a physically valid reconstruction. We also discuss the quality of the reconstruction, introducing some new error parameters.
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    Real-Time Simulation of a Stretcher Evacuation in a Large-Scale Virtual Environment
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Hubbold, Roger; Keates, Martin
    This paper presents a case study of navigation and manipulation in a large, geometrically complex, virtual environment representing an off-shore gas platform. Our approach is based on a combined force-field navigation and collision detection algorithm. After describing the basic algorithm, we extend and apply it to a real-time simulation of two avatars carrying a third avatar on a stretcher. The extensions include a probing technique, using a virtual foot and simulated gravity, to permit ascending and descending stairs and ladders. A set of constraints between the stretcher and avatars enforces realistic lifting positions. The simulation is controlled interactively with a hand-held 3D mouse. The force fields assist the user in manoeuvring through tight spaces, while collision detection guarantees that neither the stretcher nor the avatars can pass through obstructions, such as pipe-work or hand-rails. Results are presented for a case study of a complete simulation running on a PC with a moderately fast 3D graphics card. These demonstrate that the method delivers a useful frame rate for the off-shore gas platform.
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    Wavelet Radiative Transfer and Surface Interaction
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Lewis, Robert R.; Fournier, Alain
    Recently, there has been considerable interest in the representation of radiance in terms of wavelet basis functions. We will present a coordinate system called Nusselt coordinates which, when combined with wavelets, considerably simplifies computation of radiative transport and surface interaction. It also provides straightforward computation of the physical quantities involved.We show how to construct a discrete representation of the radiative transport operator ? involving inner products of smoothing functions, discuss the possible numerical integration techniques, and present an application. We also show how surface interaction can be represented as a kind of matrix product of the wavelet projections of an incident radiance and a bidirectional reflectance distribution function (BRDF).