Diatrivē--Ethnikon Metsovion Polytechneion. / Title has been changed by stamp to: Systathmisis chōrostathmikou diktyou dia neas prosengistikēs methodou. Summary in English. Vita. Bibliography: p. [110]-111.

Lantmäteriet is developing an application that can show a three-dimensional representation of Sweden based on the data that Lantmäteriet has. The purpose of this application is to be able to crowdsource improvements and changes to the map data that Lantmäteriet has, it will also be able to be used to improve a case's information for easier and faster turnaround at Lantmäteriet. In this Project, I examine how best to use this map data to generate nature such as vegetation in this application to improve usability, and make it easier for the user to know where they are in the application. During the process, I designed a nature generator that uses polygon triangulation to better generate nature.

Background. Ray marching is a technique that can be used to render images of infinite terrains defined by a height field by sampling consecutive points along a ray until the terrain surface is intersected. However, this technique can be expensive, and does not generate a mesh representation, which may be useful in certain use cases. Objectives. The aim of the thesis is to implement an algorithm for view-dependent triangulation of infinite terrains in real-time without making use of any preprocessed data, and compare the performance and visual quality of the implementation with that of a ray marched solution. Methods. Performance metrics for both implementations are gathered and compared. Rendered images from both methods are compared using an image quality assessment algorithm. Results. In all tests performed, the proposed method performs better in terms of frame rate than a ray marched version. The visual similarity between the two methods highly depend on the quality setting of the triangulation. Conclusions. The proposed method can perform better than a ray marched version, but is more reliant on CPU processing, and can suffer from visual popping artifacts as the terrain is refined.

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Certain fibered hyperbolic 3-manifolds admit a layered veering triangulation, which can be constructed algorithmically given the stable lamination of the monodromy. These triangulations were introduced by Agol in 2011, and have been further studied by several others in the years since. In the first part of this work, we obtain experimental results which shed light on the combinatorial structure of veering triangulations, and its relation to certain topological invariants of the underlying manifold. Among other things, our experimental results strongly suggest that typical veering triangulations are non-geometric, i.e., they cannot be realized as a union of isometrically embedded hyperbolic tetrahedra. In the second part, we prove that veering triangulations are in fact generically non-geometric. / Mathematics / Accompanied by two .py files. A Python interpreter is required to run a PY script in Windows.

No / This paper describes a novel procedure for thinning binary text images by generating graphical representations of words within the image. A smoothed polygonal approximation of the boundaries of each word is first decomposed into a set of contiguous triangles. Each triangle is then classified into one of only three possible types from which a graph is generated that represents the topological features of the object. Joining graph points with straight lines generates a final polygon skeleton that, by construction, is one pixel wide and fully connected. Results of applying the procedure to thinning Arabic and English handwriting are presented. Comparisons of skeleton structure and execution time with results from alternative techniques are also presented. The procedure is considerably faster than the alternatives tested when the image resolution is greater than 600 dpi and the graphical representation often needed in subsequent recognition steps is available without further processing.

Hardwood timber is a substantial economic staple in the eastern U.S., where primary hardwood processors produce more than 10 billion board feet of sawn hardwoods annually. There are over 3,500 sawmills producing hardwood lumber in the Southeastern portion of the United States. Present trends such as increasing labor costs and limited supplies of high quality logs have forced hardwood lumber manufacturers to increase their efforts to maximize the utilization of this raw material. In order to make money in such a competitive business, these sawmills must produce the highest possible grade of lumber from each saw log they process. Of all the primary and secondary processing procedures that are used to transform round wood into a final product, the sawmill edging and trimming operations have the most substantial effect on the grade and, hence, the value of the material produced. Currently, the grading of rough hardwood lumber is done manually by human inspectors according to standardized grading rules developed by the National Hardwood Lumber Association (NHLA, 1994). Standard hardwood edging and trimming operations are less than optimum because of the complexity of the grading rules, the complexity of the decision making processes involved, possible operator fatigue, and the imprecision with which lumber can be sawn by the available equipment. Studies have shown that there is a potential to increase hardwood lumber value by over 20 percent if optimum edging and trimming could be performed in hardwood sawmills. Even a small portion of this percentage would substantially increase the profit of hardwood lumber manufacturers. And this can be achieved just by utilizing some degree of automation. That is, some type of system must be designed that can scan a board to sense important hardwood features, make correct edging and trimming decisions, and then control down stream edgers and trimmers with minimal operator intervention. The most difficult part in the development of this automatic edging and trimming system is to get enough major defect information to make very good edging and trimming decisions. This thesis describes the research that was performed to build a prototype system that can collect images of boards and extract major defect information for making good edging and trimming decisions. The images that are collected include Black/White and laser profile images. Necessary defect information to be extracted for making edging and trimming decisions includes the location and size of large grading defects and areas of the board that are too thin. This thesis talks about the hardware that was used for collecting the needed board images. This includes a discussion of both the Black/White and laser profile imaging systems. The data collection boards that were used for transferring images from these imaging systems to computer memory are also described. This thesis also describes the computer vision algorithms that were developed to extract defect information needed for making improved edging and trimming decisions. Some of the processing steps involved include background extraction, both global and local segmentation, connected component labeling and small area elimination and merging. Processing results obtained of green red oak samples show that both hardware and software of the prototype system seem to work well. However, since the program needed to actually create the edging and trimming solution based on defect information found by the computer vision system was not available it was impossible to quantitatively determine the value improvement to proposed system might offer. / Master of Science

Given a set of n points on a plane, in the Minimum Weight Triangulation problem, we wish to find a triangulation that minimizes the sum of Euclidean lengths of its edges. The problem has been studied for more than four decades and is known to be incredibly challenging. In fact, the complexity status of this problem remained open until recently when it was shown to be NP-Hard. We present a novel polynomial-time algorithm that computes a 16-approximation of the minimum weight triangulation---a constant that is significantly smaller than what has been previously known. To construct our candidate solution, our algorithm uses grids to partition edges into levels by increasing weights, so that edges with similar weights appear in the same level. We incrementally triangulate the point set by constructing a growing partial triangulation for each level, introducing edges in increasing order of level. At each level, we use a variant of the ring heuristic followed by a greedy heuristic to add edges, finally resulting in a complete triangulation of the point set. In our analysis, we reduce the problem of comparing the weight of the candidate and the optimal solutions to a comparison between the cardinality of the two underlying graphs. We develop a new technique to compare the cardinality of planar straight-line graphs, and in combination with properties due to the imposed grid structure, we bound the approximation ratio. / Master of Science / Given a set of n points on a plane P, a triangulation of P is a set of edges such that no two edges intersect at a point not in P, and the edges subdivide the convex hull of P into triangles. Triangulations have a variety of applications, including computer graphics, finite element analysis, and interpolation, which motivates the need for efficient algorithms to compute triangulations with desirable qualities. The Minimum Weight Triangulation problem is the problem of computing the triangulation T that minimizes the sum of Euclidean lengths of its edges and performs well in many of the above-mentioned applications. The problem has been studied for more than four decades and is known to be incredibly challenging. In fact, the complexity status of this problem remained open until recently when it was shown to be NP-Hard. We present a novel polynomial-time algorithm that computes a 16-approximation of the minimum weight triangulation—a constant that is significantly smaller than what has been previously known. The algorithm makes use of grids together with a variant of the ring and greedy heuristic adapted to apply in a new setting, resulting in an elegant, efficient algorithm.

Notre thèse étudie la relation de soin entre les aides-soignants ou les aides médico-psychologiques et la personne cérébro-lésée (PCL). Après atteinte cérébrale, les troubles invisibles se traduisent par l’altération de la communication et la manifestation de comportements « déviants » agressifs et sexuels, provoquant l'incertitude. Dans ce contexte, cette relation comprend des enjeux concernant sa bienveillance, le sens des comportements, l'adaptabilité des pratiques, le travail émotionnel, et l’identité professionnelle. Nous interrogeons les représentations sociales de ces soignants à propos de la PCL afin d’éclairer leur travail de soin.Dans une démarche de triangulation, nous avons effectué des entretiens de recherche individuels (n=37), une enquête par questionnaire (n=130) et des focus-groups (n=4).Nos analyses apportent des connaissances sur les contenus et l’organisation des représentations sociales de la PCL chez les soignants. Ils mobilisent un savoir partagé pour définir des stratégies de communication adaptées et mettre du sens aux comportements agressifs à partir de l’état de « conscience » de la personne. Cet état oriente les pratiques et le travail émotionnel des soignants. Il apparaît une représentation de la sexualité « cérébro-lésée », pensée à partir de la représentation de la sexualité humaine, et liée à des pratiques de « mise à l’écart » de la sexualité visant à les prémunir d’une pollution symbolique.Notre recherche montre que les troubles invisibles acquièrent une visibilité par la détermination d’une « conscience » relationnelle. Les comportements agressifs et sexuels ont un statut différent au regard de la dimension symbolique de la relation. / De la dimension symbolique de la relation. Our thesis studies the care relationship between certified nursing assistants or medical-psychological assistants and the brain-injured person. After brain damage, the invisible disorders result in the alteration of communication and the manifestation of aggressive and sexual "deviant" behaviors, causing uncertainty. In this context, this relationship includes issues concerning its benevolence, the sense of behaviors, adaptability of practices, emotional labour, and professional identity. We studie the social representations of these caregivers about the brain-injured person to inform their care work.In a triangulation approach, we conducted individual research interviews (n=37), a questionnaire survey (n=130) and focus groups (n=4).Our analyzes provide knowledge about the content and organization of social representations of the brain-injured person among caregivers. They mobilize shared knowledge to define appropriate communication strategies and put meaning to aggressive behavior from the state of "consciousness" of the person. This state orients theirs practices and emotional labour. It appears a representation of "brain-injured" sexuality, thought from the representation of human sexuality, and linked to practices of "push out" sexuality to protect them from symbolic pollution.Our research shows that invisible disorders gain visibility by a relational "consciousness". Aggressive and sexual behaviors have differents status in relation to the symbolic dimension of the relationship.