This paper presents an automated face clustering method used as a preprocess of mesh generation for finite element analysis. Hundreds or thousands of faces are often contained in a CAD model designed in detail, and many of them are smaller than a single mesh element. This complexity of a CAD model makes a meshing process difficult both in quality and in speed. Our clustering method decomposes a CAD model into several regions, each of which is geometrically proper for a meshing process. In the algorithm, we start from the state where every single face makes its own region, and then repeat selecting a pair of adjacent regions and merging them into one region until there remains no mergeable pair of regions. The selection of the most suitable pair and the mergeability test are done based on several geometric indices about a pair of regions. The validity of the method is demonstrated with results of clustering and mesh generation on a real-scale CAD model. Keywords: mesh generation, clust...

This paper investigates the set of all selectively refined meshes that can be obtained from a progressive mesh. We call the set the transitive mesh space of a progressive mesh and present a theoretical analysis of the space. We define selective edge collapse and vertex split transformations, which we use to traverse all selectively refined meshes in the transitive mesh space. We propose a complete selective refinement scheme for a progressive mesh based on the transformations and compare the scheme with previous selective refinement schemes in both theoretical and experimental ways. In our comparison, we show that the complete scheme always generates selectively refined meshes with smaller numbers of vertices and faces than previous schemes for a given refinement criterion. The concept of dual pieces of the vertices in the vertex hierarchy plays a central role in the analysis of the transitive mesh space and the design of selective edge collapse and vertex split transformations.

The hierarchical radiosity algorithm solves for the global transfer of diffuse illumination in a scene. While its potential algorithmic complexity is superior to both previous radiosity methods and distributed ray tracing, for scenes containing detailed polygonal models, or highly tessellated curved surfaces, its time performance and memory consumption are less than ideal. Also, the density and orientation of the polygons in the input scene unduly affect the output of the method. The aim of this thesis will be to show that by using flexible surface hierarchies similar to those in the surface simplification literature, the use of regular refinement and to a large extent isotropic volume clusters can be avoided, increasing both the speed and the quality of the basic algorithm. I will develop a radiosity system incorporating these ideas, and show that its performance is superior to existing hierarchical radiosity algorithms, in the domain of scenes containing complex models. The underlying goal of my thesis work is to make high-quality radiosity possible with such scenes. 1

Visibility determination is the most expensive task in cluster hierarchical radiosity.

The radiosity method is one of the methods of choice used in global illumination simulation. It is a finite element technique that is particularly well suited for computing the radiance distribution in an environment exhibiting only diffuse reflection and emission. We discuss a multiresolution implementation of the technique, that has been developed to rapidly compute radiosity solutions for scenes composed of highly tessellated models. The application context is an interactive lighting design tool being developed in the framework of the DI- VERCITY project (EU-IST-13365), funded under the European IST programme (Information Society Technologies).

This report extends the work of introduced by Pacanowski et al. [PRG+ 08,PRL+ 08]. It presents a volumetric representation that captures low-frequency indirect illumination, structure intended for efficient storage and manipulation of illumination caching and on graphics hardware. It is based on a 3D texture that stores a fixed set of irradiance vectors. This texture is built during a preprocessing step by using almost any existing global illumination software. Then during the rendering step, the indirect illumination within a voxel is interpolated from its associated irradiance vectors, and is used by the fragment shader as additional local light sources. The technique can thus be considered as following the same trend as ambient occlusion or precomputed radiance transfer techniques, as it tries to include visual effects from global illumination into real-time rendering engines. But its 3D vector-based representation offers additional robustness against local variations of geometric of a scene. We also demonstrate that our technique may also be employed as an efficient and high-quality caching data structure for bidirectional rendering techniques.

Introduction 3 1.1 Purpose .......................................... 3 1.2 Method .......................................... 3 Test 2.1 2.2 2.3 2.4 2.5 2.6 framework 3 Introduction ........................................ 3 Test scenes ........................................ 4 Runtime settings ..................................... 6 2.3.1 Radiator settings ................................. 6 2.3.2 Renderpark settings ............................... 7 Measurements ....................................... 7 2.4.1 Time ........................................ 7 2.4.2 Energy transfers ................................. 7 2.4.3 Solution memory ................................. 7 Leaf elements ....................................... 8 Hardware and software platform ............................ 8 Results 8 3.3 Solution memory ..................................... 15 3.4 Leaf elements ....................................... 17 3.5 Visual evaluation ....................................

Finite Element methods are well suited to the computation of the light distribution in mostly diffuse scenes, but the resulting mesh is often far from optimal to accurately represent illumination. Shadow boundaries are hard to capture in the mesh, and the illumination may contain artifacts due to light transports at different mesh hierarchy levels. To render a high quality image a costly final gather reconstruction step is usually done, which re-evaluates the illumination integral for each pixel. In this paper an algorithm is presented which significantly speeds up the final gather by exploiting spatial and directional coherence information taken from the radiosity solution. Senders are classified, so that their contribution to a pixel is either interpolated from the radiosity solution or recomputed with an appropriate number of new samples. By interpolating this sampling pattern over the radiosity mesh, continuous solutions are obtained.

Real-time realistic rendering of a computer generated scene is one of the core research areas in computer graphics as it is required in several applications such as computer games, training simulators, medical and architectural packages and many other fields. The key factor of realism in the rendered images is the simulation of light transport based on the given lighting conditions. More natural results are achieved using luminance values near to the physical ones. However, the vast range of real luminances has a far greater range of values than what can be displayed on standard monitors. As a final step to the rendering process, a tonemapping operator needs to be applied in order to transform the values in the rendered image to displayable ones. Illumination of a scene is usually approximated with the rendering equation which solution is a computational expensive process. Moreover, the computational cost increases even more with the increase in the number of light sources and the number of vertices of the objects in the scene. Furthermore, in order to achieve high frame rates, current illumination algorithms compromise the quality with assumptions for several factors or assume static scenes so that they can exploit precomputations.

The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the National Science Foundation or the United States government. Keywords: global illumination, hierarchical radiosity, face cluster hierarchies, multiresolution The hierarchical radiosity algorithm solves for the global transfer of diffuse illumination in a scene. While its potential algorithmic complexity is superior to both previous radiosity methods and distributed ray tracing, for scenes containing detailed polygonal models, or highly tessellated curved surfaces, its time performance and memory consumption are less than ideal. My thesis is that by using hierarchies similar to those of multiresolution models, the performance of the hierarchical radiosity algorithm can be made sublinear in the number of input polygons, and thus make radiosity on scenes containing detailed models tractable. The underlying goal of my thesis work has been to make high-speed radiosity solutions possible with such scenes. To achieve this goal, a new face clustering technique for automatically partitioning polygonal models has been developed. The face clusters produced