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abstract: The tracking of multiple targets becomes more challenging in complex environments due to the additional degrees of nonlinearity in the measurement model. In urban terrain, for example, there are multiple reflection path measurements that need to be exploited since line-of-sight observations are not always available. Multiple target tracking in urban terrain environments is traditionally implemented using sequential Monte Carlo filtering algorithms and data association techniques. However, data association techniques can be computationally intensive and require very strict conditions for efficient performance. This thesis investigates the probability hypothesis density (PHD) method for tracking multiple targets in urban environments. The PHD is based on the theory of random finite sets and it is implemented using the particle filter. Unlike data association methods, it can be used to estimate the number of targets as well as their corresponding tracks. A modified maximum-likelihood version of the PHD (MPHD) is proposed to automatically and adaptively estimate the measurement types available at each time step. Specifically, the MPHD allows measurement-to-nonlinearity associations such that the best matched measurement can be used at each time step, resulting in improved radar coverage and scene visibility. Numerical simulations demonstrate the effectiveness of the MPHD in improving tracking performance, both for tracking multiple targets and targets in clutter. / Dissertation/Thesis / M.S. Electrical Engineering 2011

L’historiographie relative à la première guerre mondiale s’appuie essentiellement sur une abondante bibliographie, dans laquelle il est très difficile de trouver des documents ou études relatifs au rôle du Génie pendant le conflit. Cette thèse a pour objectif de démontrer que, dans la bataille pour Verdun, située dans la période qui va de février 1916 jusqu’en août 1917, le Génie, malgré des effectifs incontestablement très faibles, est un acteur essentiel de la victoire. Il est présent à tous les niveaux, décisionnels comme d’exécution, de la chaîne des ravitaillements qui alimente cette titanesque bataille défensive. Il est également un acteur incontournable de l’organisation du terrain qui est une des clés du succès des engagements sur ce théâtre d’opérations restreint, sur lequel sont engagés des centaines de milliers d’hommes qui se battent sous un déluge permanent d’obus de tous calibres. Enfin, il assure la continuité de l’exercice du commandement par le maintien en état de toutes les communications du champ de bataille (chemins, routes, ponts, communications téléphoniques ou optiques, etc.). Pour être efficace sur l’ensemble du spectre de ses missions, le sapeur doit s’adapter en permanence à des ordres et à des conditions d’emploi auxquels il n’est initialement pas préparé. Le commandement éparpille les capacités du Génie pour une efficacité immédiate réduite, au détriment d’actions d’ensemble beaucoup plus productives mais nécessitant des délais parfois difficilement compatibles avec le rythme des opérations. En dépit d’une action permanente au profit et aux côtés des autres armes, le Génie est trop disséminé pour retenir l’attention du commandement, apparaître dans les communiqués et marquer une mémoire collective forgée par l’image héroïque de milliers de Poilus montant à l’assaut à travers la grêle des balles de mitrailleuses et sous le déluge incessant des obus. / Historiography of the first world war is largely supported by an abundant bibliography in which it is very difficult to find documents or studies relative to the role of the Engineer during the conflict. The aim of this thesis is to demonstrate that, in the battle for Verdun, from February 1916 to August 1917, the Engineer is, despite a strength which was undeniably very weak, an essential agent in the Victory. It is present at all levels of the supply chain, decisional as well as executional, which feeds this tremendous defensive battle. It is also an indispensable actor in the organization of the battlefield which is one of the key elements of success in the engagements in this limited field of operations, in which hundred of thousands of soldiers fight under a constant storm of fire. Finally, it ensures the continuity of the operational command by maintaining all communication lines of the battlefield (paths, roads, bridges, railways, telephone lines, optic communications, etc.). In order to be efficient in the entire spectrum of its missions, the Engineer has to adapt to orders and conditions of engagements for which he is not initially prepared. The commanders spread out the engineers’ capacities for an immediate though reduced efficiency, to the detriment of the more effective collective tasks, which require a longer time frame often incompatible with the rythm of operations. Despite a permanent engagement, for and alongside the other branches, the Engineer is too diluted to gain the attention of the Commandment, be formally acknowledged and be engraved in the Memory of the Nation as are the thousands of « Poilus » rushing towards the Enemy through a hail of machine-gun bullets and shellfire.

L'analyse des cernes de croissance des arbres peut être un outil utile pour dater les événements géomorphologiques dans les régions où les données historiques sont rares ou manquantes. Dans cette étude, deux glissements de terrain rétrogressifs de la région de Fort McPherson, T.N.O, ont été étudiés par l’analyse dendrochronologique des épinettes noires (Picea mariana (Mill) BSP)) endommagées par l’évènement. Le mouvement a incliné de nombreux arbres, a endommagé leurs systèmes racinaires et les a déplacé de leur position initiale. Une trentaine d’épinettes perturbées, sur deux sites (Mélanie et Charas), ont été échantillonnées le long de la coulée de boue ainsi qu’aux limites de cette même coulée, certaines retrouvées à la verticale dans le plancher du glissement, et d’autres dans un ancien chenal abandonné. En outre, 35 épinettes bien droites, debout, intactes et non perturbées ont également été échantillonnées sur les sites afin d'établir une série de référence maitresse. Dans le premier cas, au site Mélanie, une analyse des cernes des arbres perturbés a révélé des anomalies dans la croissance des arbres. Plus précisément, une réduction des cernes de croissance a été remarquée dans les dernières années de la vie des arbres. Par ailleurs, une augmentation brutale de la largeur des cernes au même endroit a été retrouvée sur des arbres inclinés (bois de réaction). D’après des résultats, le glissement de terrain à ce site est considéré avoir eu lieu en 2002. Au deuxième site (site des Charas), en raison du nombre limité d’arbres laissés sur le terrain en plus d’une répartition spatiale assez grande, la dendrochronologie ne peut pas identifier avec précision l’année initiale du glissement de terrain du site des Charas. Les arbres se trouvant dans le sens de l'écoulement n’ont pas toujours représenté des signes de perturbation au cours d'une année en particulier, même si nous sommes convaincus qu'ils doivent avoir été localisés dans la zone touchée par l'événement. Bref, les données montrent que les perturbations à ce site se sont étalées sur plusieurs années -ce n'est donc pas un événement unique- et que tous les arbres n'ont pas tous été impactés au même degré et dans la même année.

Open-world video games give players a large environment to explore along with increased freedom to navigate and manipulate that environment. These requirements pose several problems that must be addressed by a game's graphics engine. Often there are a large number of visible objects, such as all of the trees in a forest, as well as objects comprised of large amounts of geometry, such as terrain. An open-world graphics engine must be able to render large environments at varying levels of detail and smoothly transition between detail levels to provide a believable experience. Often this involves finding a way to both store and generate the large amounts of geometry that represent the environment. In this thesis we present a system for generating and rendering large exterior environments, with a focus on terrain and vegetation. We use a region-based procedural generation algorithm to create environments of varying types. This algorithm produces content that can be rendered at multiple levels of detail. The terrain is rendered volumetrically to support caves, overhangs, and cliffs, but is also rendered using heightmaps to allow for large view distances. Vegetation is implemented using procedurally generated meshes and impostors. The volumetric terrain is editable in real time, which limits our ability to pre-generate or cache large amounts of geometry, and also limits the number of assumptions we can make with regard to visibility. We support a view distance of at least 25 miles in each direction, though distant objects are rendered at low resolution. The heightmap terrain used to achieve this view distance consists of over 360,000 triangles. Our system runs at 180 frames per second on commodity desktop hardware.

This thesis deals with rendering of large scale terrain. The first part describes theory of terrain rendering and particular level of detail techniques. Three modern intriguing algorithms are briefly depicted after this theoretical part. Main work insists on description of Geometry Clipmaps algorithm along with its optimized version GPU-Based Geometry Clipmaps. Implementation of this optimized algorithm is depicted in detail. Main advantage of this approach is incremental update of vertex data, which allows to offload overhead from CPU to GPU. In the last chapter performance of my implementation is analysed using simple benchmark.

Realistic models of landscapes are frequently needed for 3D renderings, VFX work or video games. However, modelling landscapes can be a complicated and labour-intensive task, and for this reason many algorithms have been proposed to automate the process. Among the many possible ways to create a synthetic landscape, the most common one is to simulate the various types of erosions (e.g. erosion caused by glaciers and rivers) that create real eroded landscapes, like the Grand Canyon. Many solutions have been published to simulate such terrain erosion processes in computer graphics. However the authors usually only focus on recreating a landscape at geometry level, and ignore the shading level. But surface colours and textures that match the coarse geometric features created by the erosion simulation are also essential ingredients for a believable result. And obtaining detailed surface textures by running a simulation that is able to catch all the micro-details involved is usually technically infeasible due to the involved complexity. The method that we propose attempts to get around this barrier by applying suitable detail shaders to the results of a coarse-grid erosion simulation. Specifically, we will work with a dictionary of pre-generated shaders for landscape appearance: these will be both "plain" colour...

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.

The vertical force generated from terrain-tire interaction has long been of interest for vehicle dynamic simulations and chassis development. As the terrain serves as the main excitation to the suspension system through pneumatic tire, proper terrain and tire models are required to produce reliable vehicle response. Due to the high complexity of the tire structure and the immense size of a high fidelity terrain profile, it is not efficient to calculate the terrain-tire interaction at every location. The use of a simpler tire model (e.g. point follower tire model) and a pre-filtered terrain profile as equivalent input will considerably reduce the simulation time. The desired produced responses would be nearly identical to the ones using a complex tire model and unfiltered terrain, with a significant computational efficiency improvement. In this work, a terrain pre-filtering technique is developed to improve simulation efficiency while still providing reliable load prediction. The work is divided into three parts. First a stochastic gridding method is developed to include the measurement uncertainties in the gridded terrain profile used as input to the vehicle simulation. The obtained uniformly spaced terrain is considered probabilistic, with a series of gridding nodes with heights represented by random variables. Next, a constraint mode tire model is proposed to emulate the tire radial displacement and the corresponding force given the terrain excitation. Finally, based on the constraint mode tire model, the pre-filtering technique is developed. At each location along the tire's path, the tire center height is adjusted until the spindle load reaches a pre-designated constant load. The resultant tire center trajectory is the pre-filtered terrain profile and serves as an equivalent input to the simple tire model. The vehicle response produced by using the pre-filtered terrain profile and the simple tire model is analyzed for accuracy assessment. The computational efficiency improvement is also examined. The effectiveness of the pre-filtering technique is validated on probabilistic terrain by using different realizations of terrain profiles. It is shown through multiple profiles that the computational efficiency can be improved by three orders of magnitude with no statistically significant change in resulting loading. / Ph. D.

Military unmanned aerial vehicles (UAVs) perform missions in airspace where one of the mission goals may be radar-detection avoidance. The research conducted aimed at determining optimum flight-path routes that make maximum utilization of UAV terrain masking opportunities and flight range capability in avoiding radar detection. The problem was formulated as one of constrained optimization in three dimensions and advantageous solutions were identified using Algorithm A*. The study conducted extended the substantial existing literature on radar-detection avoidance for UAVs in three significant ways: First, it explicitly modeled prominent terrain cover, such as forests and urban areas, in masking radar detection through the adaptation of a ray-casting technique in order to determine if expanded flight path cells were visible to any nearby radar. Any existing terrain cover masking prospects were exploited by the algorithm to avoid radar detection, in addition to prospects arising for terrain masking through topographical features. Second, it explicitly modeled the trade-off between detection risk and flight-path length by using a weighted average of the total flight-path length and the radar detectable flightpath length as the objective function to be minimized. The relative importance of detection risk and flight-path length is captured by adjusting the weights. Third, a mission planning process was obtained allowing route selection based on the characteristics of a portfolio of parameters and options, including radar detection exposure, the total distance traveled on a respective flight path, and a computed missile shoot-down risk benchmark for each option. The benchmark estimates the likelihood of aircraft destruction from missile impact subsequent to an integrated air defense system detection, acquisition, tracking, and missile launch sequence. The model was further extended to include provisions for preferred altitude ranges, adjustable aircraft climb and descent rate envelopes, fractional detection probability based movement costs (accounting for simultaneous detection by multiple radars), radar horizon masking, and a perspective based ellipsoidal radar cross section model. Resulting routes can be executed at a significantly lower expected cost than the alternative of using a human piloted stealth aircraft that may be required for a similar mission in the absence of intelligent route-planning.