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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.
1

Collision detection for ellipsoids and other quadrics

Choi, Yi-king., 蔡綺瓊. January 2008 (has links)
The Best PhD Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,2007-2008 / published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy
2

Sensory coding of complex visual motion in the locust (Locusta migratoria)

2013 September 1900 (has links)
The visual environment of any animal is a complex amalgamation of sensory information (Lochmann and Deneve, 2011); however, it is adaptive for an animal to only react to salient cues (Zupanc, 2010). For many organisms, the detection of an approaching object, such as an oncoming conspecific or a predator, is particularly important. An approaching object with constant velocity is called looming, and has been widely studied for evoking avoidance behaviours in a number of animal species (Gibson, 1958). The migratory locust, Locusta migratoria, has been used extensively as a model system for visually guided behaviour, due to its robust collision-avoidance behaviours and its tractable nervous system (Schlotterer, 1977). The Lobula Giant Movement Detector (LGMD) and the Descending Contralateral Movement Detector (DCMD) constitute one pathway in the locust visual system that integrates the entire field of view that has been implicated in coordinating these types of behaviours (Santer et al., 2006). Previous studies have found that the LGMD/DCMD pathway responds to many visual stimuli, including complex scenes (Rind and Simmons, 1992), approaching paired objects (Guest and Gray, 2006), objects with compound shapes (Guest and Gray, 2006), and objects that follow compound trajectories (McMillan and Gray, 2012). These findings suggest that this pathway is capable of encoding complex motion such as exists in the locust’s natural environment. In my first objective (Chapter 2), I tested the response of the locust DCMD to increasingly complex motion. Using computer generated disks that followed compound trajectories with different velocities, I demonstrate that the DCMD is capable of encoding the location, trajectory, and velocity of an approaching object through aspects of the response profile over time. The motor systems of invertebrates are often controlled by ensembles of neurons working together (Dubuc et al., 2008; Hedrich et al., 2011; Gonzalez-Bellido et al., 2013). The locust visual system has at least five identified descending neurons, beyond the DCMD, that respond to visual motion (Rowell, 1971; Griss and Rowell, 1986; Gray et al., 2010). Due to the tractability of extracellular recordings of the DCMD, these neurons remain relatively little studied. Furthermore, their responses to stimuli have not been investigated concurrently. With recent advancements in multichannel recordings and spike sorting algorithms, it is now possible to explore the responses of multiple neurons in the locust system together. In my second objective (Chapter 3), I recorded from the connective of the locust using multichannel electrodes while challenging it with a wide array of visual stimuli. Preliminary results of these experiments identified as many as five neuronal units with distinctive firing patterns, some which appear to be novel. Together, these results illustrate that the locust visual system is more complex than previously thought, through both the abilities of a single neuron to encode many aspects of visual motion and the presence of multiple unique, visually-sensitive neurons.
3

Collision detection for ellipsoids and other quadrics

Choi, Yi-king. January 2008 (has links)
Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 133-141) Also available in print.
4

Cloth simulation and collision detection using geometry images

07 June 2012 (has links)
M.Sc. (Computer Science) / A challenge faced when simulating the complex behaviour of cloth, especially at interactive frame rates, is maintaining an acceptable level of realism while keeping computation time to a minimum. A common method used to increase the performance is to decrease the number of nodes controlling the cloth's movement. This results in a significant decrease in the time taken to calculate each frame of the animation, but at the cost of sacrificing detail that can only be obtained using a dense discretisation of the cloth. A simple, efficient and popular method to simulate cloth is the mass-spring system, which utilises a regular grid of vertices representing discrete points along the cloth's surface. The structure of geometry images is similar, which makes them an ideal choice for representing arbitrary surface meshes in a cloth simulator whilst retaining the effciency of a mass-spring system. This dissertation presents a novel method of applying geometry images to cloth simulation in order to obtain cloth motion for surface meshes while retaining the simplicity of a massspring model. By adapting an implicit/explicit integration scheme, and utilising the regular structure of geometry images, an improvement in performance is achieved. Additionally, the cloth is able to drape over other objects, also represented as geometry images. The proposed method is efficient enough to allow fairly dense cloth meshes to be simulated in real-time.
5

Swept areas and collision detection with application to autonomous vehicles

Sundberg, Sofia January 2005 (has links)
This thesis presents an algorithm for collision detection for an autonomous articulated vehicle following pregenerated paths in a mining environment. Two types of vehicles are studied. The tricycle vehicle and the articulated vehicle. The characteristics of the mine is presented. A way of using these characteristics is studied. An algorithm for collision detection using the swept area of the vehicle following a pregenerated path is given. As proof of concept a small implementation is also given along, with a few examples. / Validerat; 20101217 (root)
6

Développement d'un système d'avertissemment sonore, validé par EEG, basé sur des approches vision et acoustique pour la detection de véhicules approchants des véhicules moteur deux roues / Visual and acoustic techniques for motorcycle collision warning system with EEG validation

Muzammel, Muhammad 03 July 2018 (has links)
Dans de nombreux pays, le taux de mortalité des motocyclistes est beaucoup plus élevé que celui des autres conducteurs de véhicules. Parmi de nombreux autres facteurs, les collisions arrière des motocyclettes contribuent fortement à ces décès de motards. Les systèmes de détection de collision peuvent être utilisés pour minimiser ces accidents mortels. Cependant, la plupart des systèmes de détection de collision existants n'identifient pas le type de danger potentiel auquel sont exposés les motocyclistes. Chaque système d'alerte de collision utilise une technique de détection de collision distincte, ce qui limite ses performances et rend impératif l'étude de son efficacité. Malheureusement, aucun travail de ce type n'a été signalé dans ce domaine particulier pour les motocyclistes. Par conséquent, il est important d'étudier la réponse physiologique du motocycliste contre ces systèmes d'alerte de collision. Dans cette recherche, une méthode de détection et de classification des véhicules approchant par l'arrière est présentée. Pour la détection de collision, une approche basee vision et la technique basee sur le son ont été utilisées. Pour les techniques visuelles et acoustiques, des caractéristiques d'apparence et de spectre de puissance ont été utilisées, respectivement, pour détecter le véhicule qui s'approche à l'extrémité arrière de la motocyclette. En ce qui concerne la classification des véhicules, seule une technique acoustique est utilisée; un spectre de puissance acoustique et des caractéristiques énergétiques sont utilisés pour classer les véhicules qui approchent. Deux types d'ensembles de données, à savoir des ensembles de données acquises durant ce travail (obtenues en plaçant une caméra à l'arrière d'une motocyclette) et des ensembles de données disponibles telechargeables (pour la détection visuelle et pour la classification audio des véhicules) sont utilisés pour la validation. La méthodologie proposée a permis de détecter et de classer les véhicules pour des ensembles de données acquises durent cette these. De même, pour les ensembles de données disponibles , le taux positif vrai le plus élevé et le taux de détection faux le plus faible ont été atteints par rapport aux méthodes de l etat de l art. En outre, une étude physiologique basée sur le potentiel lié à l'événement (ERP) a été réalisée sur les motocyclistes afin d'étudier leurs réponses vis-à-vis du système d'alerte de collision arrière. Deux types d'avertissements auditifs (c'est-à-dire verbal et buzzer) sont utilisés pour ce système d'avertissement. Pour étudier la réponse des motocyclistes, les composantes N1, N2, P3 et N400 ont été extraits des données d'électroencéphalographie (EEG). Ces systèmes d avertissement ont montré des effets positifs au niveau des neuronal sur les motocyclistes et réduisent leur temps de réaction et les ressources attentionnelles nécessaires pour traiter correctement la cible. En résumé, le système d'avertissement de collision par l'arrière proposé avec des avertissements verbaux auditifs augmente considérablement la vigilance du motocycliste et peut être utile pour éviter les scénarios possibles de collision arrière. / In many countries, motorcyclist fatality rate is much higher than that of other vehicle drivers. Among many other factors, motorcycle rear-end collisions are also contributing to these biker fatalities. Collision detection systems can be used to minimize these fatalities. However, most of the existing collision detection systems do not identify the type of potential hazard faced by motorcyclists. Every collision warning system used a distinctive collision detection technique, which limits its performance and makes it imperative to study its effectiveness. Unfortunately, no such work has been reported in that particular domain for motorcyclists. Therefore, it is important to study the physiological response of the motorcyclist against these collision warning systems. In this research, a rear end vehicle detection and classification method is presented for motorcyclists. For collision detection, vision technique and acoustic technique have been used. For visual and acoustic techniques, appearance features and power spectrum have been used, respectively, to detect the approaching vehicle at the rear end of the motorcycle. As for the vehicle classification, only an acoustic technique is utilized; an acoustic power spectrum and energy features are used to classify the approaching vehicles. Two types of datasets which are comprised of self-recorded datasets (obtained by placing a camera at the rear end of a motorcycle) and online datasets (for vision-based vehicle detection and for audio based vehicle classification techniques) are used for validation. Proposed methodology successfully detected and classified the vehicle for self-recorded datasets. Similarly, for online datasets, the higher true positive rate and less false detection rate has been achieved as compared to the existing state of the art methods. Moreover, an event-related potential (ERP) based physiological study has been performed on motorcyclists to investigate their responses towards the rear end collision warning system. Two types of auditory warnings (i.e., verbal and buzzer) are used for this warning system. To study the response of the motorcyclists, the N1, N2, P3, and N400 components have been extracted from the Electroencephalography (EEG) data. These introduced systems have shown positive effects at neural levels on motorcyclists and reduce their reaction time and attentional resources required for processing the target correctly. In summary, the proposed rear-end collision warning system with auditory verbal warnings significantly increases the alertness of the motorcyclist and can be helpful to avoid the possible rear-end collision scenarios.
7

Collision Detection for Moving Polyhedra

Canny, John 01 October 1984 (has links)
We consider the problem of moving a three dimensional solid object among polyhedral obstacles. The traditional formulation of configuration space for this problem uses three translational parameters and three angles (typically Euler angles), and the constraints between the object and obstacles involve transcendental functions. We show that a quaternion representation of rotation yields constraints which are purely algebraic in a higher-dimensional space. By simple manipulation, the constraints may be projected down into a six dimensional space with no increase in complexity. Using this formulation, we derive an efficient exact intersection test for an object which is translating and rotating among obstacles.
8

An evaluation of grid based broad phase collision detection for real time interactive environments

Liljeby, Jonas January 2011 (has links)
Detailed and exact collision detection for large amounts of objects has for a long time been a non real-time affair because of the immense amount of computations necessary. This was however not only because of the complexity of the algorithms but also because discussed of the computations would not have had to be done in the first place. This paper has through literature research and empirical testing examined two different broad phase approaches to object culling in a three dimensional environment. The aim of such a broad phase algorithm is to decrease the amount of computation heavy narrow phase collision detection checks and thus enhancing application performance. Potential weaknesses of these approaches were addressed and possible solutions discussed. Performance comparisons were made to give a better overview of what kind of performance enhancements can be expected and to give a theoretical base for further research.
9

Development and Evaluation of a Virtual Haptic Environment

Lin, Chun-yu 13 July 2004 (has links)
As the progress of computer, virtual reality has become a more and more widespread technology and is applied extensively in entertainment, training, or medical science. To increase the interaction and reality of the virtual technology, the development of haptic feedback improves rapidly in recent years. This paper focuses on judgment existing collision detection algorithms, virtual wall models, and friction models from the view point of man-machine interface. A virtual environment interface with force feedback by using a joystick for computer game as a haptic device is established. A virtual environment is also built by employing the DirectX, a 3D computer graphic software developed by Microsoft Corp. Three virtual wall models are compared and four operational experiments are conducted to explore the influence of force feedback on operation task in virtual environment.
10

A Hierarchical Hexagon Data Structure for Collision Detection

Kang, Ting-wei 28 July 2001 (has links)
In this paper, hexagonal grid is extended to hierarchical structure. This technique can be applied to collision detection. By using concept of node, we develop an effectually linear decode called ¡§HCD¡¨. To develop to three dimensions, the structure of octahedron is applied to develop hexagonal hierarchical structure in three dimensions. This is helpful to simulate objects and approximate objects. The object¡¦s data is commonly deposited in float. In this paper, Symmetrical Hexagonal Frame makes whole object to be deposited in integer. So the data of object can be compressed to smaller size. Otherwise, by concept of k-dops, we can close to object¡¦s real surfaces with hierarchical hexagonal structures at low level.

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