Building Footprint Extraction from LiDAR Data and Imagery Information

This study presents an automatic method for regularisation of building outlines. Initially, building segments are extracted using a new fusion method. Data- and model-driven approaches are then combined to generate approximate building polygons. The core part of the method includes a novel data-driven algorithm based on likelihood equation derived from the geometrical properties of a building. Finally, the Gauss-Helmert and Gauss-Markov models adjustment are implemented and modified for regularisation of building outlines considering orthogonality constraints

Light scattering in a turbulent cloud: Simulations to explore cloud-chamber experiments

Radiative transfer through clouds can be impacted by variations in particle number size distribution, but also in particle spatial distribution. Due to turbulent mixing and inertial effects, spatial correlations often exist, even on scales reaching the cloud droplet separation distance. The resulting clusters and voids within the droplet field can lead to deviations from exponential extinction. Prior work has numerically investigated these departures from exponential attenuation in absorptive and scattering media; this work takes a step towards determining the feasibility of detecting departures from exponential behavior due to spatial correlation in turbulent clouds generated in a laboratory setting. Large Eddy Simulation (LES) is used to mimic turbulent mixing clouds generated in a laboratory convection cloud chamber. Light propagation through the resulting polydisperse and spatially correlated particle fields is explored via Monte Carlo ray tracing simulations. The key finding is that both mean radiative flux and standard deviation about the mean differ when correlations exist, suggesting that an experiment using a laboratory convection cloud chamber could be designed to investigate non-exponential behavior. Total forward flux is largely unchanged (due to scattering being highly forward-dominant for the size parameters considered), allowing it to be used for conditional sampling based on optical thickness. Direct and diffuse forward flux means are modified by approximately one standard deviation. Standard deviations of diffuse forward and backward fluxes are strongly enhanced, suggesting that fluctuations in the scattered light are a more sensitive metric to consider. The results also suggest the possibility that measurements of radiative transfer could be used to infer the strength and scales of correlations in a turbulent cloud, indicating entrainment and mixing effects

Flight Dynamics Nonlinearity Assessment Across a New Aerodynamic Attitude Flight Envelope

A new asymmetric level aerodynamic attitude flight envelope is introduced in this dissertation. The aerodynamic attitude envelope is an angle of attack vs. sideslip angle region which describes the extent of where an aircraft can sustain a steady slipping horizontal flight condition. The new envelope is thus an extension of the more common speed-altitude symmetric level flight envelope. This new envelope can be used for design requirements, dynamic analysis, control synthesis, or performance comparison. Moreover, this envelope provides enhanced insight into trimability-controllability limitations within the aircraft design model. The aerodynamic attitude flight envelope is constructed for a six degree of freedom nonlinear simulation model of a high-performance aircraft. The constructed envelope is found to be asymmetric with respect to positive vs. negative sideslip values, due to the inherent asymmetry in the aerodynamic model database. Asymmetry and offset in the force and moment coefficient data could originate from experimental error, from model fabrication imperfections, from vortex-dominated flow, from data reduction flaws, or from other sources. The literature shows that vortex-dominated flow can cause significant side force, rolling moment, and yawing moment coefficient asymmetries. Details concerning the removal of asymmetry and offset in the aerodynamic data are given. The purpose behind removing the asymmetry and offset is to facilitate analysis of the new aerodynamic attitude flight envelope with an ideal aircraft model so that fundamental relationships can be more easily observed, and to provide a comparison with the non-ideal case previously computed. Based on the adapted and symmetrized aerodynamic data, a new aerodynamic attitude asymmetric level flight envelope is constructed and introduced. Further, the six degree of freedom aircraft simulation model is analyzed with nonlinear index theory across this nontraditional flight envelope. Aircraft dynamic properties often change in a nonlinear way across operating conditions. Nonlinear index theory provides a new concept for measuring the strength of these changes for a given set of coordinates and is applied to the asymmetric aerodynamic attitude envelope with the original and the adapted and symmetrized aerodynamic data. This analysis provides new methodology and new insights into aircraft dynamics and control. The index analysis exposes certain flight condition regions in which nonlinearity strength is high. These regions are further investigated with both linear and nonlinear simulations. Because the nonlinearity index is based on the matrix two-norm, the index can sometimes overestimate the nonlinear strength. To circumvent this behavior, indices based on system matrix partitions and normalized state formulations are explored. Nonlinearity is a function of the coordinates used to express the dynamic system. Therefore, the nonlinearity index is also applied to the aircraft model, expressed with three different frame of reference sets for kinetics and kinematics, in order to determine the best, or most linear, coordinates among the three investigated sets

Heterogeneous Self-Reconfiguring Robotics

Self-reconfiguring (SR) robots are modular systems that can autonomously change shape, or reconfigure, for increased versatility and adaptability in unknown environments. In this thesis, we investigate planning and control for systems of non-identical modules, known as heterogeneous SR robots. Although previous approaches rely on module homogeneity as a critical property, we show that the planning complexity of fundamental algorithmic problems in the heterogeneous case is equivalent to that of systems with identical modules. Primarily, we study the problem of how to plan shape changes while considering the placement of specific modules within the structure. We characterize this key challenge in terms of the amount of free space available to the robot and develop a series of decentralized reconfiguration planning algorithms that assume progressively more severe free space constraints and support reconfiguration among obstacles. In addition, we compose our basic planning techniques in different ways to address problems in the related task domains of positioning modules according to function, locomotion among obstacles, self-repair, and recognizing the achievement of distributed goal-states. We also describe the design of a novel simulation environment, implementation results using this simulator, and experimental results in hardware using a planar SR system called the Crystal Robot. These results encourage development of heterogeneous systems. Our algorithms enhance the versatility and adaptability of SR robots by enabling them to use functionally specialized components to match capability, in addition to shape, to the task at hand

Conservative From-Point Visibility.

Visibility determination has been an important part of the computer graphics research for several decades. First studies of the visibility were hidden line removal algorithms, and later hidden surface removal algorithms. Today’s visibility determination is mainly concentrated on conservative, object level visibility determination techniques. Conservative methods are used to accelerate the rendering process when some exact visibility determination algorithm is present. The Z-buffer is a typical exact visibility determination algorithm. The Z-buffer algorithm is implemented in practically every modern graphics chip. This thesis concentrates on a subset of conservative visibility determination techniques. These techniques are sometimes called from-point visibility algorithms. They attempt to estimate a set of visible objects as seen from the current viewpoint. These techniques are typically used with real-time graphics applications such as games and virtual environments. Concentration is on the view frustum culling and occlusion culling. View frustum culling discards objects that are outside of the viewable volume. Occlusion culling algorithms try to identify objects that are not visible because they are behind some other objects. Also spatial data structures behind the efficient implementations of view frustum culling and occlusion culling are reviewed. Spatial data structure techniques like maintaining of dynamic scenes and exploiting spatial and temporal coherences are reviewed.1. Introduction.............................................................................................................1 2. Visibility Problem...................................................................................................3 3. Scene Organization...............................................................................................10 3.1. Bounding Volume Hierarchies and Scene Graphs.................................10 3.2. Spatial Data Structures ...............................................................................13 3.3. Regular Grids...............................................................................................14 3.4. Quadtrees and Octrees ...............................................................................15 3.5. KD-Trees.......................................................................................................20 3.6. BSP-Trees......................................................................................................23 3.7. Exploiting Spatial and Temporal Coherence ..........................................27 3.8. Dynamic Scenes...........................................................................................30 3.9. Summary ......................................................................................................34 4. View Frustum Culling .........................................................................................35 4.1. View Frustum Construction ......................................................................36 4.2. View Frustum Test......................................................................................37 4.3. Hierarchical View Frustum Culling .........................................................41 4.4. Optimizations ..............................................................................................42 4.5. Summary ......................................................................................................44 5. Occlusion Culling .................................................................................................45 5.1. Fundamental Concepts...............................................................................45 5.2. Occluder Selection.......................................................................................46 5.3. Hardware Occlusion Queries....................................................................49 5.4. Object-Space Methods ................................................................................50 5.5. Image-Space Methods ................................................................................55 5.6. Summary ......................................................................................................64 6. Conclusion.............................................................................................................66 References .................................................................................................................... 7

Granite: A scientific database model and implementation

The principal goal of this research was to develop a formal comprehensive model for representing highly complex scientific data. An effective model should provide a conceptually uniform way to represent data and it should serve as a framework for the implementation of an efficient and easy-to-use software environment that implements the model. The dissertation work presented here describes such a model and its contributions to the field of scientific databases. In particular, the Granite model encompasses a wide variety of datatypes used across many disciplines of science and engineering today. It is unique in that it defines dataset geometry and topology as separate conceptual components of a scientific dataset. We provide a novel classification of geometries and topologies that has important practical implications for a scientific database implementation. The Granite model also offers integrated support for multiresolution and adaptive resolution data. Many of these ideas have been addressed by others, but no one has tried to bring them all together in a single comprehensive model. The datasource portion of the Granite model offers several further contributions. In addition to providing a convenient conceptual view of rectilinear data, it also supports multisource data. Data can be taken from various sources and combined into a unified view. The rod storage model is an abstraction for file storage that has proven an effective platform upon which to develop efficient access to storage. Our spatial prefetching technique is built upon the rod storage model, and demonstrates very significant improvement in access to scientific datasets, and also allows machines to access data that is far too large to fit in main memory. These improvements bring the extremely large datasets now being generated in many scientific fields into the realm of tractability for the ordinary researcher. We validated the feasibility and viability of the model by implementing a significant portion of it in the Granite system. Extensive performance evaluations of the implementation indicate that the features of the model can be provided in a user-friendly manner with an efficiency that is competitive with more ad hoc systems and more specialized application specific solutions