Dissertations / Theses on the topic 'Tree rendering'

Over the last few years, the computer graphics hardware has evolved extremely fast from supporting only a few fixed graphical algorithms to support execution of dynamic programs supplied by a developer. Only a few years back all graphics programs were written in assembly language, a nonintuitive low level programming language. Today such programs can be written in high level, near written English, source code, making it easier to develop more advanced effects and geometric shapes on the graphics card. This project presents a new way to utilize today's programmable graphics card to generate and render trees for real-time applications. The emphasis will be on generating and rendering the geometry utilizing the graphics hardware, trying to speed up the calculation of naturally advanced shapes for the purpose of offloading the systems central processing unit.

Tento projekt se věnuje problematice zobrazení velkých hierarchických struktur, zejména možnostem vizualizace stromových grafů. Cílem je implementace hyperbolického prohlížeče ve webovém prostředí, který využívá potenciálu neeukleidovské geometrie k promítnutí stromu na hyperbolickou rovinu. Velký důraz je kladen na uživatelsky přívětivou manipulaci se zobrazovaným modelem a snadnou orientaci.

The main contribution of this thesis is a parametric method for generation of single-mesh polygonal tree models that follow natural rules as indicated by da Vinci in his notebooks. Following these rules allow for a relatively simple scheme of connecting branches to parent branches. Proper branch connection is a requirement for gaining the benefits of subdivision. Techniques for proper texture coordinate generation and subdivision are also explored.The result is a tree model generation scheme resulting in single polygonal meshes susceptible to various subdivision methods, with a Catmull-Clark approximation method as the evaluated example.As realistic visualization of tree models is the overall objective, foliage appearance and the impression of a dense branching structure is considered. A shader-based method for accurately faking high branch density at a distance is explored.

Geographical Information Systems and geospatial data are seeing widespread use in various internet and mobile mapping applications. One of the areas where such technologies can be particularly valuable is aeronautical navigation. Pilots use paper charts for navigation, which, in contrast to modern mapping software, have some limitations. This project aims to develop an iOS application for phones and tablets that uses a GeoPackage database containing aeronautical geospatial data, which is rendered on a map to create an offline, feature-based mapping software to be used for navigation. Map features are selected from the database using R-Tree spatial indices. The attributes from each feature within the requested bounds are evaluated to determine the styling for that feature. Each feature, after applying the aforementioned styling, is drawn to an interactive map that supports basic zooming and panning functionalities. The application is written in Swift 3.0 and all features are drawn using iOS Core Graphics

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.

Land use regulations are typically established as a response to development activity. For effective growth management and habitat preservation, the opposite should occur. This study considers tree preservation ordinances of the Dallas-Fort Worth metropolitan area as a means of evaluating development regulation in a metropolitan context. It documents the impact urban cores have on regulations and policies throughout their region, demonstrating that the same urban-rural gradient used to describe physical components of our metropolitan areas also holds true in terms of policy formation. Although sophistication of land use regulation generally dissipates as one moves away from an urban core, native habitat is more pristine at the outer edges. To more effectively protect native habitat, regional preservation measures are recommended.

La représentation des phénomènes météorologiques est un enjeu essentiel en Informatique Graphique dans l’optique d’obtenir des scènes extérieures visuellement réalistes. Depuis quelques années, les chercheurs se sont penchés sur la simulation de la pluie en synthèse d’images. Ce mémoire a pour but de présenter deux méthodes de rendu : une première méthode pour le rendu de la pluie, et une seconde pour le rendu des égouttements provenant des arbres. Notre modèle de rendu de pluie est une méthode multi-échelle permettant de tenir compte des propriétés locales et globales de ce phénomène. Nous avons réussi à mettre en corrélation la densité des gouttes proches de l’observateur (échelle mésoscopique) avec l’atténuation de la visibilité (échelle macroscopique), en fonction d’un seul paramètre global cohérent : l’intensité des précipitations. Cette méthode a fait l’objet d’une publication [56] dans la revue Computers & Graphics en 2015. D’autre part, nous basons notre méthode pour le rendu des égouttements sur une approche phénoménologique. Une telle approche s’avère plus adaptée pour gérer les grands espaces, et présente l’avantage d’être indépendante de la complexité de la scène. L’approche choisie s’appuie sur des expérimentations et des mesures hydrologiques effectuées par des chercheurs spécialisés dans l’hydrologie des forêts. Nous proposons ainsi un modèle d’égouttement cohérent, tenant compte des propriétés intrinsèques à chaque type d’arbres. Cette méthode a fait elle aussi l’objet d’une présentation à la conférence Eurographics Symposium on Rendering (EGSR) ainsi qu’une publication [57] au journal Computer Graphics Forum (CGF) en 2016
This dissertation aims to present a coherent multiscale model for real-time rain rendering which takes into account local and global properties of rainy scenes. Our goal is to simulate visible rain streaks close to the camera as well as the progressive loss of visibility induced by atmospheric phenomena. Our model proposes to correlate the attenuation of visibility, which is due in part to the extinction phenomenon, and the distribution of raindrops in terms of rainfall intensity and camera's parameters. Furthermore, this method proposes an original rain streaks generation based on spectral analysis and sparse convolution theory. This allows an accurate control of rainfall intensity and streaks appearance, improving the global realism of rainy scenes. We also aim at rendering interactive visual effects inherent to complex interactions between trees and rain in real-time in order to increase the realism of natural rainy scenes. Such a complex phenomenon involves a great number of physical processes influenced by various interlinked factors and its rendering represents a thorough challenge in Computer Graphics. We approach this problem by introducing an original method to render drops dripping from leaves after interception of raindrops by foliage. Our method introduces a new hydrological model representing interactions between rain and foliage through a phenomenological approach. Our model reduces the complexity of the phenomenon by representing multiple dripping drops with a new fully functional form evaluated per-pixel on-the-fly and providing improved control over density and physical properties. Furthermore, an efficient real-time rendering scheme, taking full advantage of latest GPU hardware capabilities, allows the rendering of a large number of dripping drops even for complex scenes

The project has been carried out at, and in association with, Micronic Laser Systems AB in Täby, Sweden. Micronic Laser Systems, manufacture laser pattern generators for the semiconductor and display markets. Laser pattern generators are used to create photomasks, which are a key component in the microlithographic process of manufacturing microchips and displays.

An essential problem to all modern semiconductor manufacturing is the constantly decreasing sizes of features and increasing use of resolution enhancement techniques (RET), leading to ever growing sizes of datasets describing the semiconductors. When sizes of datasets reach magnitudes of hundreds of gigabytes, visualisation, navigation and editing of any such dataset becomes extremely difficult. As of today this problem has no satisfying solution.

The project aims at the proposal of a geometry engine that effectively can deal with the evergrowing sizes of modern semiconductor lithography. This involves a new approach to handling data, a new format for spatial description of the datasets, hardware accelerated rendering and support for multiprocessor and distributed systems. The project has been executed without implying changes to existing data formats and the resulting application is executable on Micronics currently existing hardware platforms.

The performance of the new viewer system surpasses any old implementation by a varying factor. If rendering speed is the comparative factor, the new system is about 10-20 times faster than its old counterparts. In some cases, when hard disk access speed is the limiting factor, the new implementation is only slightly faster or as fast. And finally, spatial indexing allow some operations that previously lasted several hours, to complete in a few seconds, by eliminating all unnecessary disk-reading operations.

Tree models created by an industry used package are exported and the structure extracted in order to procedurally regenerate the geometric mesh, addressing the limitations of the application's standard output. The structure, once extracted, is used to fully generate a high quality skeleton for the tree, individually representing each section in every branch to give the greatest achievable level of freedom of deformation and animation. Around the generated skeleton, a new geometric mesh is wrapped using a single, continuous surface resulting in the removal of intersection based render artefacts. Surface smoothing and enhanced detail is added to the model dynamically using the GPU enhanced tessellation engine. A real-time snow accumulation system is developed to generate snow cover on a dynamic, animated scene. Occlusion techniques are used to project snow accumulating faces and map exposed areas to applied accumulation maps in the form of dynamic textures. Accumulation maps are xed to applied surfaces, allowing moving objects to maintain accumulated snow cover. Mesh generation is performed dynamically during the rendering pass using surface o�setting and tessellation to enhance required detail.

The work described in this thesis is part of the Open Space project, a collaboration between Linköping University, NASA and the American Museum of Natural History. The long-term goal of Open Space is a multi-purpose, open-source scientific visualization software. The thesis covers the research and implementation of a pipeline for preparing and rendering volumetric data. The developed pipeline consists of three stages: A data formatting stage which takes data from various sources and prepares it for the rest of the pipeline, a pre-processing stage which builds a tree structure of of the raw data, and finally an interactive rendering stage which draws a volume using ray-casting. The pipeline is a fully working proof-of-concept for future development of Open Space, and can be used as-is to render space weather data using a combination of suitable data structures and an efficient data transfer pipeline. Many concepts and ideas from this work can be utilized in the larger-scale software project.

Rendering of natural scenes has interested the scientific community for a long time due to its numerous applications. The targeted goal is to create images that are similar to what a viewer can see in real life with his/her eyes. The main obstacle is complexity: nature scenes from real life contain a huge number of small details that are hard to model, take a lot of time to render and require a huge amount of memory unavailable in current computers. This complexity mainly comes from geometry and lighting. The goal of our research is to overcome this complexity and to achieve real-time rendering of nature scenes while providing visually convincing dynamic global illumination. Our work focuses on grass and trees as they are commonly visible in everyday life. We handle geometry and lighting complexities for grass to render millions of grass blades interactively with dynamic lighting. As for lighting complexity, we address real-time rendering of trees by proposing a lighting model that handles indirect lighting. Our work makes extensive use of the current generation of Graphics Processing Units (GPUs) to meet the real-time requirement and to leave the CPU free to carry out other tasks.
Ph.D.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Computer Science PhD

Previous research from environmental psychology shows that human well-being suffers in windowless environments in many ways and a window view of nature is psychologically and physiologically beneficial to humans. Current window substitutes, still images and video, lack three dimensional properties necessary for a realistic viewing experience – primarily motion parallax. We present a new system using a head-coupled display and image-based rendering to simulate a photorealistic artificial window view of nature with motion parallax. Evaluation data obtained from human subjects suggest that the system prototype is a better window substitute than a static image and has significantly more positive effects on observers’ moods. The test subjects judged the system prototype as a good simulation of, and acceptable replacement for, a real window, and accorded it much higher ratings for realism and preference than a static image.

Medical imaging is an important part of the clinical workflow. With the increasing amount and complexity of image data comes the need for automatic (or semi-automatic) analysis methods which aid the physician in the exploration of the data. One specific imaging technique is angiography, in which the blood vessels are imaged using an injected contrast agent which increases the contrast between blood and surrounding tissue. In these images, the blood vessels can be viewed as tubular structures with varying diameters. Deviations from this structure are signs of disease, such as stenoses introducing reduced blood flow, or aneurysms with a risk of rupture. This thesis focuses on segmentation and visualization of blood vessels, consituting the vascular tree, in angiography images. Segmentation is the problem of partitioning an image into separate regions. There is no general segmentation method which achieves good results for all possible applications. Instead, algorithms use prior knowledge and data models adapted to the problem at hand for good performance. We study blood vessel segmentation based on a two-step approach. First, we model the vessels as a collection of linear structures which are detected using multi-scale filtering techniques. Second, we develop machine-learning based level set segmentation methods to separate the vessels from the background, based on the output of the filtering. In many applications the three-dimensional structure of the vascular tree has to be presented to a radiologist or a member of the medical staff. For this, a visualization technique such as direct volume rendering is often used. In the case of computed tomography angiography one has to take into account that the image depends on both the geometrical structure of the vascular tree and the varying concentration of the injected contrast agent. The visualization should have an easy to understand interpretation for the user, to make diagnostical interpretations reliable. The mapping from the image data to the visualization should therefore closely follow routines that are commonly used by the radiologist. We developed an automatic method which adapts the visualization locally to the contrast agent, revealing a larger portion of the vascular tree while minimizing the manual intervention required from the radiologist. The effectiveness of this method is evaluated in a user study involving radiologists as domain experts.

碩士
國立臺灣師範大學
資訊教育學系
93
L-system is usually used in a computer graphic system to draw the natural landscape with regular patterns, like plants, cloud, mountain, sea images. L-system consists of regular rules and simple syntax with graphic meaning to generate realistic and complicate pictures. This research is based on L-system to describe the Fractal Tree. First, we develop a rendering scheme to draw Fractal Trees in two dimensional plane and three dimensional space by SVG（Scalable Vector Graphics）. In general, as the repetition count rises in the L-system grammar, the branch count of a Fractal Tree raises exponentially. As a result, geometric objects within the Fractal Tree also grow exponentially. Therefore, we propose several graphics object compression methods to decrease the number of geometric objects. Our methods include SVG source code optimization schemes (i.e., Line Merge, Segment Merge, Code Merge) and data compressing scheme using GZIP technology. The effective compression ration of our prototype system is among 20% to 70%. This research has effectively compressed the SVG objects of the Fractal Tree, which enables users to view more complex Fractal Tree image with less storage and network bandwidth.

This paper introduces the delta tree, a data structure that represents an object using a set of reference images. It also describes an algorithm for generating arbitrary re-projections of an object by traversing its delta tree. Delta trees are an efficient representation in terms of both storage and rendering performance. Each node of a delta tree stores an image taken from a point on a sampling sphere that encloses the object. Each image is compressed by discarding pixels that can be reconstructed by warping its ancestor's images to the node's viewpoint. The partial image stored at each node is divided into blocks and represented in the frequency domain. The rendering process generates an image at an arbitrary viewpoint by traversing the delta tree from a root node to one or more of its leaves. A subdivision algorithm selects only the required blocks from the nodes along the path. For each block, only the frequency components necessary to reconstruct the final image at an appropriate sampling density are used. This frequency selection mechanism handles both antialiasing and level-of-detail within a single framework. A complex scene is initially rendered by compositing images generated by traversing the delta trees of its components. Once the reference views of a scene are rendered once in this manner, the entire scene can be reprojected to an arbitrary viewpoint by traversing its own delta tree. Our approach is limited to generating views of an object from outside the object's convex hull. In practice we work around this problem by subdividing objects to render views from within the convex hull.

碩士
國立清華大學
資訊工程學系
93
Tree-rendering is still an open problem because of high complexity and fractal-like structure consisted in a tree. With two image sequences describing moving paths around a tree and toward a tree, we can synthesize an image sequence that a user walking in the space spanned by the two paths of the two image sequences. Our algorithm works by extracting one image from the source image sequence, and driving pixels in that image with a sequence of displacement field constructed from the original image sequence that corresponds to the desired path specified in advance. Holes are occurred due to this unstable synthesis process, so several methods are presented to synthesize needed information i.e. displacement, color for holes for further synthesis process.

碩士
國立中興大學
資訊科學研究所
91
Pen-and-Ink illustrations have the superiors of simplifying unnecessary messages, conveying important information, better carriage, and lower demands of storage, so that it had been used for architecture, medical photographing, and ancient books. Trees play a role of greening circumstances, beautifying home-land functions in our lives, however the Pen-and-Ink illustrations majoring on trees are less to be researched and discovered. This thesis makes Pen-and-Ink illustrations as the research issue, and enumerates trees for example. Our goal is to develop an effective rendering algorithm with Pen-and-Ink illustrations style based on trees. Similar to Deussen, we use 3D tree models as input, and then render skeleton and leaves separately. In the aspect of skeleton, in order to keep the coherence among frames, we adopt texture mapping to produce the variance of shades and brightness of the skeleton surfaces. According to the relationship between the surface and the light, we can judge whether the object is on the facing-light or not, and then project the stroke textures on the surface. Unlike producing the direction and length of strokes randomly, the coherence among frames can be controlled effectively, and the efficiency is also satisfying. In the aspect of leaves, Deussen’s depth difference algorithm can’t detect the outlines of leaves precisely. While rendering, it needs to adjust complex variables settings. Therefore, we propose filter algorithm and standard deviation algorithm to improve these disadvantages. Filter algorithm that is based on Sobel kernel calculates the gradient vectors of pixels to detect the changes of edges of horizontal and vertical directions, and judges if the pixel belongs to outlines using the magnitude of gradient vector. Filter algorithm detects more precise leaves outlines than depth difference algorithm does. The standard deviation algorithm whish is based on the statistics concept analyzes the average of the depth values of pixels. With the differences between depth value and averages of pixels, we can get the changes of the depth values of pixels and easily predict the outlines of leaves. The standard deviation algorithm detects outlines of the leaves more precise than the depth difference algorithm, and doesn’t adjust the threshold. The experimental results show that the quantity of the images using our methods is superior to Deussen’s depth difference algorithm, and it also can achieve real-time rendering. We think if we can add graftal and the shadow of tree in the Pen-and-Ink illustrations of trees to fill up the blank area of illustrations, the composition of an image will be more accomplished. Therefore, we propose a non-uniform distribution algorithm, which can take non-uniform samples according to the distance to the tree according some kind of probability density function we developed. In the aspect of the shadow of tree, we project the vertices of 3D tree models on the ground, and then randomly choose some of the projected vertices on the ground. Finally we attach the grasses model on the location of sampling point, to produce the effects of graftal and the shadow of tree. In real-time browsing, when the observer is far from the tree, the depth difference algorithm can’t detect the outline of leaves precisely. Deussen propose the silhouette recover algorithm can resolve this problem effectively. But when the observer is too close to the tree, the algorithm will produce exceeding outline of leaves. Therefore, we propose the near distances recover algorithm to make up the short of Deussen’s algorithm. Finally, we implement a system called “Pen-and-Ink Style of Trees Illustration Rendering System” according to above proposed algorithms. Users can easily select different rendering algorithms or adjust the viewpoint or other parameters to generate effectively an illustration of tree with Pen-and-Ink style. In this thesis, we propose a texture mapping of strokes in the aspect of skeleton, the filter algorithm and the standard deviation algorithm for rendering leaves, the near distances recover algorithm for real-time browsing, and finally implement the “Pen-and-Ink Style of Tree Illustration Rendering System”. In the static rendering, it needn’t adjust the threshold for the convenient on rendering and the outlines are more precise and exact. Besides, attaching the graftal and tree shadow makes the composition of an image more attractive. When dynamic browsing, it could produce five images of Pen-and-Ink style of tree illustration per second, and can maintain coherence among frames. In conclusion, our rendering algorithms can produce fine-quality outlines of Pen-and-Ink style of tree illustration, and can achieve real-time rendering and interactive browsing. We think our research has a great contribution on the Pen-and-Ink style of tree illustration rendering.

This thesis describes the development of a system for the procedural generation and painterly rendering of trees. Specifically, the rendered trees are modeled after those found in the oil landscape paintings of 19th century French painter Camille Corot. The rendering system, which is a combination of MEL-scripted Maya tools and Renderman shaders, facilitates the creation of still images that look convincingly painterly, as well as 3D animations with temporal coherence. Brush stroke properties are animated based on distance from the camera, so that traditional painting techniques for representing depth are incorporated into the computer-generated animations. During the development process, the system was generalized to apply to other structures, such as grass and rocks, and allows for the creation and rendering of entire landscapes. Several example animations were created with the system to demonstrate the ideas developed during the process and the quality of the results.