Background. A previous study on performance benefits of joint reduction for animations was made by the authors of this thesis. The results of the study showed that a reduction in joint count is highly beneficial for performance. What that study left out was the perception of Level of Detail (LoD) of animations, and what the Just Noticeable Difference (JND) of a percentage decrease on the joint count would be. Thus motivating a study on peoples’ perception of animation quality. Objectives. The aim is to study the perception of LoD of animations in a game-like environment whilst doing a simple search-and-click task. Aiming to find the JND between animations with a different number of joints while the players are set with a task that does not involve interacting with the characters performing the animation. Methods. A psychophysical experiment was performed using a game implementation in Unity. Unity was chosen because it has easy access to develop scripts and a game environment. Furthermore, it has a marketplace where already made content can be downloaded and reused, which made the user study much easier to create. Results. A total of 85.71% did not see any difference between the different qualities used for the animations. The 14.29% that saw a difference in the animations all saw the difference between the lowest and the one next to the lowest quality animation. Conclusions. Three out of 21 participants were able to see a difference in the lowest animation quality, whilst no one saw any difference in the other qualities. Thus, people were not able to see a density reduction of up to 62.26% fewer joints for the chosen animation. Due to the low number of positive detections in the quality change of the animations, the JND could not be reliably computed.

<p>To render outdoor scenes with lots of vegetation in real time is a big challenge. This problem has important applications in the areas of visualization and simulation. Some progress has been made the last years, but a previously unsolved difficulty has been to combine high rendering quality with abundant variation in scenes. </p><p>I present a method to mathematically generate and render vegetation in real time, with implementation in the scene graph Gizmo3D. The most important quality of the method is its ability to render scenes with many unique specimens with very low aliasing. </p><p>To obtain real time performance, a hierarchical level-of-detail scheme (LOD- scheme) is used which facilitates generation of vegetation in the desired level- of-detail on the fly. The LOD-scheme is texture-based and uses textures that are common for all specimens of a whole species. The most important contribution is that I combine this LOD-scheme with the use of semi- transparency, which makes it possible to obtain low aliasing. </p><p>Scenes with semi-transparency require correct rendering order. I solve this problem by introducing a new method for approximate depth sorting. An additional contribution is a variant of axis-aligned billboards, designated blob, which is used in the LOD-scheme. Furthermore, building blocks consisting of small branches are used to increase generation performance.</p>

<p>Simulation of modern battlefield scenarios on consumer PC:s deal with a number of limitations, many of them related to the limited performance of a normal PC compared to workstations and servers. Specifically, the visualization of realistic large scale outdoor environments is problematic because of the large amount of data required to describe its contents. This becomes especially problematic in simulations of fast moving vehicles such as aircrafts, where one needs to maintain high frame rates while having high visual detail for orientation and targeting. This thesis proposes a method of generating realistic outdoor environments from actual geological data and then rendering it efficiently using an improved level of detail algorithm within a proprietary battle simulation framework. We also show how to integrate an open source Flight Dynamics Model (FDM) into the simulation framework for future hybrid simulations involving aircrafts.</p>

To render outdoor scenes with lots of vegetation in real time is a big challenge. This problem has important applications in the areas of visualization and simulation. Some progress has been made the last years, but a previously unsolved difficulty has been to combine high rendering quality with abundant variation in scenes. I present a method to mathematically generate and render vegetation in real time, with implementation in the scene graph Gizmo3D. The most important quality of the method is its ability to render scenes with many unique specimens with very low aliasing. To obtain real time performance, a hierarchical level-of-detail scheme (LOD- scheme) is used which facilitates generation of vegetation in the desired level- of-detail on the fly. The LOD-scheme is texture-based and uses textures that are common for all specimens of a whole species. The most important contribution is that I combine this LOD-scheme with the use of semi- transparency, which makes it possible to obtain low aliasing. Scenes with semi-transparency require correct rendering order. I solve this problem by introducing a new method for approximate depth sorting. An additional contribution is a variant of axis-aligned billboards, designated blob, which is used in the LOD-scheme. Furthermore, building blocks consisting of small branches are used to increase generation performance.

Rendering large terrains on large screens at interactive frame rates is a challenging area of computer graphics. In the last decade, real-time terrain rendering on large screens played a significant role in various simulations and virtual reality systems. To fulfill the demand of these systems, two software tools are developed. The first tool is a Terrain Editor that creates and manipulates large terrains. The second is a Multi-Display Viewer that displays the created terrains on multiple screens. Since the typical large terrains consist of many polygons, graphics boards might have difficulties in rendering the terrain at interactive frame rates. The common solution to this problem is to use terrain simplification without losing image quality. To this purpose, in this study, a paged level of detail mechanism that works with multiple threads is developed and integrated on multiple screen display systems to increase the performance of the high resolution systems.

We present a method for representing seams in clothing animation, and its application in simulation level of detail. Specifically we consider cloth represented as a regular grid of particles connected by spring-dampers, and a seam specified by a closed set of parametric trim curves in the cloth domain. Conventional cloth animation requires the tessellation of seams so that they are handled uniformly by the dynamics process. Our goal is a seam definition which does not constrain the attached clothing panels to be of the same resolution, or even constant resolution, while not being a hindrance to the dynamics process. We also apply our seams to cloth defined on a regular grid, as opposed to the irregular meshes commonly used with seams. The determination of particles interior to the cloth panel can be done using wellknown graphics operations such as scan-conversion. Due to the particle-based nature of the simulation, the dynamics approach combines easily with existing implicit and explicit methods. Finally, because the seams are resolution independent, the particle density per clothing panel can be adjusted as desired. This gives rise to a simple application of the given seams approach illustrating how it may be used for simulation level of detail.

<p>Denna rapport presenterar ett alternativt sätt att ljussätta terräng i datorgrafik. Tidigare modeller har vanligtvis byggt på lokal ljussättning, som inte tar hänsyn till kringliggande geometri, och har med en extra process approximerat effekten av ljusinteraktionen. Genom att använda sig av en teknik som kallas precomputed radiance transfer (PRT) kan man förberäkna hur en punkt interagerar med ljus för olika inkommande riktningar och undviker därmed att göra detta under programkörningen. Det är viktigt att denna teknik även fungerar tillsammans med level-of-detail (LOD) terrängrenderingsalgoritmer eftersom rendering av alla trianglar i terrängen för varje skärmuppdatering inte är optimalt för dagens grafikkort. Man vill därför representera den underliggande terrängen med fler trianglar närmare betraktaren och färre längre bort. Motiveringen till detta är att trianglar längre ifrån betraktaren kommer resultera i färre pixlar på skärmen, så att rendera större trianglar gör en liten visuell skillnad. Arbetet visar på att tekniken fungerar med LOD-terrängrenderingsalgoritmer med bra prestanda och visuell kvalitet.</p>

Syftet med denna studie var att visa vilka konsekvenser valet av en viss detaljnivå får vid simuleringen av ett system bestående av mjukvara, hårdvara och mekaniska komponenter. Till detta syfte ställdes två frågeställningar “Vad blir konsekvenserna av att lägga sig på en viss detaljnivå vid simulering av ett system bestående av mjukvara, hårdvara och mekaniska komponenter?” och “Hur påverkar detaljnivån när en simulering av ett system bestående av mjukvara, hårdvara och mekaniska komponenter ska verifieras och valideras?”. För att genomföra denna studie och uppnå syftet användes en vanligt förekommande metod för att utveckla simuleringsmodeller. Studien visade på att detaljnivån påverkar vilken information en modell kräver för att konstrueras och vilket användningsområde en modell har. Resultaten tyder på att informationen som finns tillgänglig om det system som en modell ska utvecklas för helt eller delvis begränsar vilken detaljnivå som modellen kan utvecklas på. Studien har begränsat undersökningen till en typ av växelspak och de två modeller som utvecklades ligger på en hög detaljnivå. Examensarbetet har även inte undersökt utvecklingen av modeller, enbart färdiga modeller. / The purpose of this study was to show what consequences a particular level of detail has on the simulation of a system consisting of software, hardware and mechanical components. In order to fulfil this purpose, the following questions were asked: “What are the consequences of using a certain level of detail in a simulation of a system containing software, hardware, and mechanical components?” and “How does the level of detail affect when a simulation of a system containing software, hardware, and mechanical components is verified and validated?”. To carry out this study, a common method for developing simulation models was used. The study showed that the level of detail will affect what information a model requires to be constructed and which uses a model has at that level of detail. The results suggest that the available information about the system that a model is developed for partially restricts the level of detail the model can have. The study is limited to a single type of shifter and all models have been developed at a high level of detail. The study also did not examine the development of models, and only studied finished models.

Many applications in computer graphics and related fields can benefit fromautomatic simplification of complex polygonal surface models. Applications areoften confronted with either very densely over-sampled surfaces or models toocomplex for the limited available hardware capacity. An effective algorithmfor rapidly producing high-quality approximations of the original model is avaluable tool for managing data complexity. In this dissertation, I present my simplification algorithm, based on iterativevertex pair contraction. This technique provides an effective compromisebetween the fastest algorithms, which often produce poor quality results, andthe highest-quality algorithms, which are generally very slow. For example, a1000 face approximation of a 100,000 face model can be produced in about 10seconds on a PentiumPro 200. The algorithm can simplify both the geometryand topology of manifold as well as non-manifold surfaces. In addition toproducing single approximations, my algorithm can also be used to generatemultiresolution representations such as progressive meshes and vertex hierarchiesfor view-dependent refinement. The foundation of my simplification algorithm, is the quadric error metricwhich I have developed. It provides a useful and economical characterization oflocal surface shape, and I have proven a direct mathematical connection betweenthe quadric metric and surface curvature. A generalized form of this metric canaccommodate surfaces with material properties, such as RGB color or texturecoordinates. I have also developed a closely related technique for constructing a hierarchyof well-defined surface regions composed of disjoint sets of faces. This algorithminvolves applying a dual form of my simplification algorithm to the dual graphof the input surface. The resulting structure is a hierarchy of face clusters whichis an effective multiresolution representation for applications such as radiosity.

This report describes an algorithm for computing 3D object hierarchies fit for hlod optimization. The algorithm is used as a pre-processing stage in an hlod pipeline that automatically optimizes 3D models containing multiple meshes. The algorithm for generating hierarchies groups together meshes in a hierarchical tree using operations on bounding spheres of the meshes. The algorithm prioritizes grouping close objects together in the early stages, and relaxes its constraints toward the end, resulting in a tree structure with a single root node. The hierarchical tree is then used by computing proxy meshes, i.e. simplified stand-in meshes, for the inner nodes of the hierarchy. Finally, the resulting proxy meshes, together with the generated hierarchy and the original meshes, are used to render the model using a tree-traversing hlod switching algorithm that renders deeper parts of the tree containing more detailed meshes when more detail is needed. In addition, a minor change to the clustering algorithm is proposed. By swapping the bounding spheres to AABBs (Axis-Aligned Bounding Boxes) in the clustering stage, hierarchies with different properties are generated. This change is shown to generate hierarchies with similar rendering performance as the hierarchies made with bounding spheres, while at the same time resulting in lower space requirements for all proxy meshes. Overall, the proposed automatic hlod pipeline is shown to increase rendering performance for all evaluated scenes in most frames, while never yielding noticeably worse performance than the original model as well.