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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
261

On-line uppdragsplanering baserad på prediktionsreglering / On-line mission planning based on Model Predictive Control

Sjanic, Zoran January 2001 (has links)
Modern air battles are very dynamic and fast, and put extreme pressure on pilots. In some unpredictable situations, like new discovered threats or mission plan deviation because of enemy aircraft, the pilots might need to replan their predefined flight route. This is very difficult, if not impossible, to do since numerous factors affect it. A system that can help the pilots to do such a thing is needed. P revious work in this field has involved methods from artificial intelligence like A*-search. In this master thesis, implementation of a replanning system based on a control theory method, Model Predictive Control (MPC), is examined. Different factors influencing the path, such as terrain and threats, are included in the algorithm. The results presented in this thesis show that MPC solves the problem. As with every method there are some drawbacks and advantages, but as a summary the method is a very promising one and is worth further development. Proposals of future work and different improvements of the algorithms used here are presented in this report as well.
262

Real-time Trajectory Optimization for Terrain Following Based on Non-linear Model Predictive Control / Trajektorieoptimering för terrängföljning i realtid baserad på olinjär prediktionsreglering

Flood, Cecilia January 2001 (has links)
There are occasions when it is preferable that an aircraft flies asclose to the ground as possible. It is difficult for a pilot to predict the topography when he cannot see beyond the next hill, and this makes it hard for him to find the optimal flight trajectory. With the help of a terrain database in the aircraft, the forthcoming topography can be found in advance and a flight trajectory can be calculated in real-time. The main goal is to find an optimal control sequence to be used by the autopilot. The optimization algorithm, which is created for finding the optimal control sequence, has to be run often and therefore, it has to be fast. This thesis presents a terrain following algorithm based on Model Predictive Control which is a promising and robust way of solving the optimization problem. By using trajectory optimization, a trajectory which follows the terrain very good is found for the non-linear model of the aircraft.
263

Contribution à l'étude de quelques formations de flysch et de molasse des Alpes et réflexions sur les critères distinctifs de ces deux faciès

Kogblevi, Jean Claude 27 February 1973 (has links) (PDF)
Dans la 1°partie sont étudiés les affleurements . Un historique sur l'origine des termes flysch et molasse est fait. La 2° partie aborde les résultats des méthodes utiliséees sur le terrain : stratonomie; figures sédimentaires; litage etc .. Les résultats obtenus en laboratoires sont étudiés en 3° partie. La 4° partie s'interesse aux caractères génétiques des deux faciés. En 5° partie : un essai de conclusion
264

Essai sur la reconstruction du vide : l'exemple du Faubourg Saint-Laurent

Hudon, Pascal 11 1900 (has links) (PDF)
Le faubourg Saint-Laurent, quartier central de Montréal, est incapable d'attirer des projets architecturaux aptes à combler ses vides, conséquences des pratiques architecturales modernistes des années cinquante et soixante. Les citoyens se sont approprié ces vides en raison de leurs propriétés hétérotopiques (Foucault, 1967) et s'opposent à tout projet qui détruira le lien privilégié qui s'est développé entre eux et cette ouverture de l'espace. Parce qu'il est le seul à maintenir ce lien, le seul aménagement convenable est l'espace public. L'officialisation du vide diminue la capacité de la ville à se régénérer. Ces oppositions aux projets démontrent l'impact d'une culture d'immobilisme (phénomène NIMBY) et de la crainte du changement. Pour assurer l'évolution de la ville, particulièrement des quartiers centraux, nous devons trouver des projets acceptables et des processus qui en permettent l'acceptation. Une étude philosophique de l'impact du vide sur la population a déterminé que son appropriation existait de façon psychologique, par la création d'un projet architectural personnel qui invalidait ainsi tout autre projet. Ces espaces sont hétérotopiques par leur capacité à représenter toutes et aucune des fonctions à la fois. Notre hypothèse affirme qu'une nouvelle définition de l'ouverture de l'espace, et ce tant physique que visuelle, préserverait les propriétés hétérotopiques des vides actuels. L'ouverture de l'espace arraché et aménagé a contribué à la création d'une nouvelle définition du besoin d'ouverture de l'espace. Les typologies résidentielles actuelles sont incapables de défendre cette nouvelle définition de l'ouverture de l'espace. Actuellement, de nouvelles typologies ne peuvent apparaître à cause notamment de la réglementation inappropriée, d'une structure de consultations publiques inefficace et en raison du manque de volonté politique. Les liens entre le vide et le plein nécessitent une profonde reconsidération. La relation actuelle, qui a rejeté celle du mouvement moderniste, n'est pas conséquente des besoins existants, des valeurs populaires et de l'évolution des techniques de construction. Le faubourg Saint-Laurent mérite qu'on s'attarde encore à son sort. Une série de nouveaux projets affirment être en mesure de redonner la vitalité au secteur. Ces solutions, bien que souhaitables, n'arriveront pas seules à rétablir l'environnement construit du quartier. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Montréal, modernisme, appropriation, vide, faubourg Saint-Laurent
265

Real-time rendering of very large 3D scenes using hierarchical mesh simplification

Jönsson, Daniel January 2009 (has links)
Captured and generated 3D data can be so large that it creates a problem for today's computers since they do not fit into the main or graphics card memory. Therefore methods for handling and rendering the data must be developed. This thesis presents a way to pre-process and render out-of-core height map data for real time use. The pre-processing uses a mesh decimation API called Simplygon developed by Donya Labs to optimize the geometry. From the height map a normal map can also be created and used at render time to increase the visual quality. In addition to the 3D data textures are also supported. To decrease the time to load an object the normal and texture maps can be compressed on the graphics card prior to rendering. Three different methods for covering gaps are explored of which one turns out to be insufficient for rendering cylindrical equidistant projected data.At render time two threads work in parallel. One thread is used to page the data from the hard drive to the main and graphics card memory. The other thread is responsible for rendering all data. To handle precision errors caused by spatial difference in the data each object receives a local origin and is then rendered relative to the camera. An atmosphere which handles views from both space and ground is computed on the graphics card.The result is an application adapted to current graphics card technology which can page out-of-core data and render a dataset covering the entire earth at 500 meters spatial resolution with a realistic atmosphere.
266

Large Scale Terrain Modelling for Autonomous Mining

Norberg, Johan January 2010 (has links)
This thesis is concerned with development of a terrain model using Gaussian Processes to support the automation of open-pit mines. Information can be provided from a variety of sources including GPS, laser scans and manual surveys. The information is then fused together into a single representation of the terrain together with a measure of uncertainty of the estimated model. The model is also used to detect and label specific features in the terrain. In the context of mining, theses features are edges known as toes and crests. A combination of clustering and classification using supervised learning detects and labels these regions. Data gathered from production iron ore mines in Western Australia and a farm in Marulan outside Sydney is used to demonstrate and verify the ability of Gaussian Processes to estimate a model of the terrain. The estimated terrain model is then used for detecting features of interest.Results show that the Gaussian Process correctly estimates the terrain and uncertainties, and provide a good representation of the area. Toes and crests are also successfully identified and labelled.
267

The Difficulty of Designing a General Heuristic Agent Navigation Strategy

Fors, Mikael, Hermelin, Madelen January 2011 (has links)
We consider an abstract representation of some environment in which an agent is located. Given a goal sequence, we ask what strategy said agent - utilizing readily available algorithmic tools - should incorporate to successfully find a valid traversal route such that it is optimal in accordance with a predefined error-margin. We present four scenarios that each incorporate aspects common to general navigation to further illustrate some of the difficult problems needed to be solved in any general navigation strategy. Two reinforcement learning and four graph path planning algorithms are studied and applied on said predefined scenarios. Through the introduction of a long-term strategy model we allow comparative study of the result of the applications, and note a distinct difference in performance. Further, we discuss the lack of a probabilistic algorithmic approach and why it should be an option in any general strategy as it allows verifiably "good" estimated solutions, useful when the problem at hand is NP-hard. Several meta-level concepts are introduced and discussed to further illustrate the difficulty in producing an optimal strategy with an explicit long-term horizon. We argue for a non-deterministic approach, looking at the apparent gain of epsilon-randomness when incorporated by a reinforcement learning agent. Several problems that may arise with non-determinism are discussed, based on the notion that such an agents' performance can be viewed as a markov chain; possibly resulting in suboptimal paths concerning norm.
268

Terrain Aided Underwater Navigation using Bayesian Statistics / Terrängstöttad undervattensnavigering baserad på Bayesiansk statistik

Karlsson, Tobias January 2002 (has links)
For many years, terrain navigation has been successfully used in military airborne applications. Terrain navigation can essentially improve the performance of traditional inertial-based navigation. The latter is typically built around gyros and accelerometers, measuring the kinetic state changes. Although inertial-based systems benefit from their high independence, they, unfortunately, suffer from increasing error-growth due to accumulation of continuous measurement errors. Undersea, the number of options for navigation support is fairly limited. Still, the navigation accuracy demands on autonomous underwater vehicles are increasing. For many military applications, surfacing to receive a GPS position- update is not an option. Lately, some attention has, instead, shifted towards terrain aided navigation. One fundamental aim of this work has been to show what can be done within the field of terrain aided underwater navigation, using relatively simple means. A concept has been built around a narrow-beam altimeter, measuring the depth directly beneath the vehicle as it moves ahead. To estimate the vehicle location, based on the depth measurements, a particle filter algorithm has been implemented. A number of MATLAB simulations have given a qualitative evaluation of the chosen algorithm. In order to acquire data from actual underwater terrain, a small area of the Swedish lake, Lake Vättern has been charted. Results from simulations made on this data strongly indicate that the particle filter performs surprisingly well, also within areas containing relatively modest terrain variation.
269

Interactive Editing Of Complex Terrains On Parallel Graphics Architectures

Gun, Ufuk 01 September 2009 (has links) (PDF)
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.
270

Object-based Classification Of Landforms Based On Their Local Geometry And Geomorphometric Context

Gercek, Deniz 01 April 2010 (has links) (PDF)
Terrain as a continuum can be categorized into landform units that exhibit common physiological and morphological characteristics which might serve as a boundary condition for a wide range of application domains. However, heterogeneous views, definitions and applications on landforms yield inconsistent and incompatible nomenclature that lack interoperability. Yet, there is still room for developing methods for establishing a formal background for general type of classification models to provide different disciplines with a basis of landscape description that is also commonsense to human insight. This study proposes a method of landform classification that reveals general geomorphometry of the landscape. Landform classes that are commonsense to human insight and relevant to various disciplines is adopted to generate landforms at the landscape scale. Proposed method integrates local geometry of the surface with geomorphometric context. A set of DTMs at relevant scale are utilized where local geometry is represented with morphometric DTMs, and geomorphometric context is incorporated through relative terrain position and terrain network. &ldquo / Object-based image analysis (OBIA)&rdquo / tools that have the ability to segment DTMs into more representative terrain objects and connect those objects in a multi-level hierarchy is adopted. A fuzzy classification approach is utilized via semantic descriptions to represent ambiguities both in attribute and geographical space. Method is applied at different case areas to evaluate the efficiency and stability of the classification. Outcomes portray reasonable amount of consistency where the results can be utilized as general or multi-purpose regarding some ambiguity that is inherent in landforms as well.

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