Robert F. Tobler

Combined rendering of polarization and fluorescence effects

We propose a practicable way to include both polarization and fluorescence effects in a rendering system at the same time. Previous research in this direction only demonstrated support for either one of these phenomena; using both effects simultaneously was so far not possible, mainly because the techniques for the treatment of polarized light were complicated and required rendering systems written specifically for this task. The key improvement over previous work is that we use a different, more easily handled formalism for the description of polarization state, which also enables us to include fluorescence effects in a natural fashion. Moreover, all of our proposals are straightforward extensions to a conventional spectral rendering system.

An analytical model for skylight polarisation

Under certain circumstances the polarisation state of the illumination can have a significant influence on the appearance of scenes; outdoor scenes with specular surfaces - such as water bodies or windows - under clear, blue skies are good examples of such environments. In cases like that it can be essential to use a polarising renderer if a true prediction of nature is intended, but so far no polarising skylight models have been presented. This paper presents a plausible analytical model for the polarisation of the light emitted from a clear sky. Our approach is based on a suitable combination of several components with well-known characteristics, and yields acceptable results in considerably less time than an exhaustive simulation of the underlying atmospheric scattering phenomena would require.

Real-time occlusion culling with a lazy occlusion grid

We present a new conservative image-space occlusion culling method to increase the rendering speed of very large general scenes on todays available hardware without time-expensive preprocessing. The method is based on a low-resolution grid upon a conventional z-buffer. The occlusion information in the grid is updated in a lazy manner. In comparison to related methods this significantly reduces the number of pixels that have to be read from the z-buffer. The grid allows fast decisions if an object is occluded or potentially visible. It is used together with a bounding volume hierarchy that is traversed in a front-to-back order and which allows to cull large parts of the scene at once. A special front-to-back traversal is used if no pixel-level query for the furthest z-value of an image area is available. We show that the method works efficiently on todays available hardware and we compare it with related methods.

Separating semantics from rendering: a scene graph based architecture for graphics applications

A large number of rendering and graphics applications developed in research and industry are based on scene graphs. Traditionally, scene graphs encapsulate the hierarchical structure of a complete 3D scene, and combine both semantic and rendering aspects. In this paper, we propose a clean separation of the semantic and rendering parts of the scene graph. This leads to a generally applicable architecture for graphics applications that is loosely based on the well-known Model-View-Controller (MVC) design pattern for separating the user interface and computation parts of an application. We explore the benefits of this new design for various rendering and modeling tasks, such as rendering dynamic scenes, out-of-core rendering of large scenes, generation of geometry for trees and vegetation, and multi-view rendering. Finally, we show some of the implementation details that have been solved in the process of using this software architecture in a large framework for rapid development of visualization and rendering applications.

A Hierarchical Subdivision Algorithm for Stochastic Radiosity Methods

The algorithm proposed in this paper uses a stochastic approach to incrementally calculate the illumination function over a surface. By tracking the illumination function at different levels of meshing resolution, it is possible to get a measure for the quality of the current representation, and to adaptively subdivide in places with inadequate accuracy. With this technique a hierarchical mesh that is based on the stochastic evaluation of global illumination is generated.

A multiresolution mesh generation approach for procedural definition of complex geometry

As a general approach to procedural mesh definition we propose two mechanisms for mesh modification: generalized subdivision and rule based mesh growing. In standard subdivision, a specific subdivision rule is applied to a mesh to get a succession of meshes converging to a limit surface. A generalized approach allows different subdivision rules at each level of the subdivision process. By limiting the variations introduced at each level, convergence can be ensured: however in a number of cases it may be of advantage to exploit the expressivity of different subdivision steps at each level, without imposing any limits. Rule based mesh growing is an extension of L-systems to not only work on symbols, but connected symbols, representing faces in a mesh. This mechanism allows the controlled introduction of more complex geometry in places where it is needed to model fine details. Using both these mechanisms in combination we demonstrate, that a great variety of complex objects can be easily modeled and compactly represented.

Fast light-map computation with virtual polygon lights

We propose a new method for the fast computation of light maps using a many-light global-illumination solution. A complete scene can be light mapped on the order of seconds to minutes, allowing fast and consistent previews for editing or even generation at loading time. In our method, virtual point lights are clustered into a set of virtual polygon lights, which represent a compact description of the illumination in the scene. The actual light-map generation is performed directly on the GPU. Our approach degrades gracefully, avoiding objectionable artifacts even for very short computation times.

A new Form Factor Analogy and its Application to Stochastic Global Illumination Algorithms

A new form factor analogy, that has been derived from results of integral geometry, is introduced. The new analogy is shown to be useful for stochastic evaluation of the local form of the rendering equation used in various Monte Carlo methods for calculating global illumination. It makes it possible to improve importance sampling in these methods, thereby speeding up convergence. A new class of bidirectional reflection distribution functions that directly benefits from the analogy and permits exact evaluation and calculation of correctly distributed vectors for Monte Carlo integration is presented.

Interactive content for presentations in virtual reality

In this paper, we develop concepts for presenting interactive content in form of a slideshow in a virtual environment, similar to conventional desktop presentation software. We demonstrate how traditional content like text and images can be integrated into 3D models and embedded applications to form a seamless presentation combining the advantages of traditional presentation methods with 3D interaction techniques and different 3D output devices. We demonstrate how different combinations of output devices can be used for presenter and audience, and discuss their various advantages.

New Efficient Algorithms with Positive Definite Radiosity Matrix

New efficient algorithms will be presented for solving diffuse radiosity problems, involving advantages of progressive radiosity. Demonstration of the algorithms and of their convergence relies on the new form of the radiosity equations, with a positive definite matrix. The methods have been tested with a new error formula, the (area-weighted) average relative error. The form with a symmetric, positive definite matrix penetrates into the gist of the radiosity problem deeper than the former radiosity or power variable equations. At the same time this makes it possible to apply several algorithms well-known from numerical analysis. In general, the positive definite form leads to algorithms, which are mathematically handleable, and of proven convergence and effectiveness.