Thesis (MScEng)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: This thesis presents the design and implementation of an autonomous navigational system and the automation of a practical demonstrator vehicle. It validates the proposed navigation architecture using simple functional navigational modules on the said vehicle. The proposed navigation architecture is a hierarchical structure, with a mission planner at the top, followed by the route planner, the path planner and a vehicle controller with the vehicle hardware at the base. A vehicle state estimator and mapping module runs in parallel to provide feedback data. The controls of an all terrain vehicle are electrically actuated and equipped with feedback sensors to form a complete drive-by-wire solution. A steering controller and velocity control state machine are designed and implemented on an existing on-board controller that includes a six degrees-of-freedom kinematic state estimator. A lidar scanner detects obstacles. The lidar data is mapped in real time to a local three-dimensional occupancy grid using a Bayesian update process. Each lidar beam is projected within the occupancy grid and the occupancy state of a ected cells is updated. A lidar simulation environment is created to test the mapping module before practical implementation. For planning purposes, the three-dimensional occupancy grid is converted to a two-dimensional drivability map. The path planner is an adapted rapidly exploring random tree (RRT) planner, that assumes Dubins car kinematics for the vehicle. The path planner optimises a cost function based on path length and a risk factor that is derived from the drivability map. A simple mission planner that accepts user-de ned waypoints as objectives is implemented. Practical tests veri ed the potential of the navigational structure implemented in this thesis. / AFRIKAANSE OPSOMMING: In hierdie tesis word die ontwerp en implementering van 'n outonome navigasiestelsel weergegee, asook die outomatisering van 'n praktiese demonstrasievoertuig. Dit regverdig die voorgestelde navigasie-argitektuur op die bogenoemde voertuig deur gebruik te maak van eenvoudige, funksionele navigasie-modules. Die voorgestelde navigasie-argitektuur is 'n hi erargiese struktuur, met die missie-beplanner aan die bo-punt, gevolg deur die roetebeplanner, die padbeplanner en voertuigbeheerder, met die voertuighardeware as basisvlak. 'n Voertuigtoestandsafskatter en karteringsmodule loop in parallel om terugvoer te voorsien. Die kontroles van 'n vierwiel-motor ets is elektries geaktueer en met terugvoersensors toegerus om volledig rekenaarbeheerd te wees. 'n Stuur-beheerder en 'n snelheid-toestandmasjien is ontwerp en ge mplementeer op 'n bestaande aanboordverwerker wat 'n kinematiese toestandsafskatter in ses grade van vryheid insluit. 'n Lidar-skandeerder registreer hindernisse. Die lidar-data word in re ele tyd na 'n lokale drie-dimensionele besettingsrooster geprojekteer deur middel van 'n Bayesiese opdateringsproses. Elke lidar-straal word in die besettingsrooster geprojekteer en die besettingstoestand van betrokke selle word opdateer. 'n Lidar-simulasie-omgewing is geskep om die karteringsmodule te toets voor dit ge mplementeer word. Die drie-dimensionele besettingsrooster word na 'n twee-dimensionele rybaarheidskaart verwerk vir beplanningsdoeleindes. Die padbeplanner is 'n aangepaste spoedig-ontdekkende-lukrake-boom en neem Dubinskar kinematika vir die voertuig aan. Die padbeplanner optimeer 'n koste-funksie, gebaseer op padlengte en 'n risiko-faktor, wat vanaf die rybaarheidskaart verkry word. 'n Eenvoudige missie-beplanner, wat via-punte as doelstellings neem, is ge mplementeer. Praktiese toetsritte veri eer die potensiaal van die navigasiestruktuur, soos hier beskryf.

Mechanically Stabilized Earth (MSE) walls retain soil on steep, unstable slopes with crest loads. Over the last decade, they are becoming quite popular due to their low cost-to-benefit ratio, design flexibility, and ease of construction. Like any civil infrastructure, MSE walls need to be continuously monitored according to transportation asset management criteria during and after the construction stage to ensure that their expected serviceability measures are met and to detect design and/or construction issues, which could lead to structural failure. Current approaches for monitoring MSE walls are mostly qualitative (e.g., visual inspection or examination). Besides being time consuming, visual inspection might have inconsistencies due to human subjectivity. Other monitoring approaches are based on using total station, geotechnical field instrumentations, and/or Static Terrestrial Laser Scanning (TLS). These instruments are capable of providing highly accurate, reliable performance measures. However, the underlying data acquisition and processing strategies are time-consuming and are not scalable. This research focuses on a comprehensive strategy using a Mobile LiDAR Mapping System (MLS) for the acquisition and processing of point clouds covering the MSE wall. The strategy produces standard serviceability measures, as defined by the American Association of State Highway and Transportation Officials (AASHTO) – e.g., longitudinal and transversal angular distortions. It also delivers a set of recently developed measures (e.g., out-of-plane offsets and 3D position/orientation deviations for individual panels constituting the MSE wall). Moreover, it is also capable of handling MSE walls with smooth or textured panels with the latter being the focus of this research due to its more challenging nature. For this study, an ultra-high-accuracy wheel-based MLS has been developed to efficiently acquire reliable data conducive to the development of the standard and new serviceability measures. To illustrate the feasibility of the proposed acquisition/processing strategy, two case studies in this research have been conducted with the first one focusing on the comparative performance of static and mobile LiDAR in terms of the agreement of the derived serviceability measures. The second case study aims at illustrating the feasibility of the proposed strategy in handling large textured MSE walls. Results from both case studies confirm the potential of using MLS for efficient, economic, and reliable monitoring of MSE walls.