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

VLSI Routing for Advanced Technology

Routing is a major step in VLSI design, the design process of complex integrated circuits (commonly known as chips). The basic task in routing is to connect predetermined locations on a chip (pins) with wires which serve as electrical connections. One main challenge in routing for advanced chip technology is the increasing complexity of design rules which reflect manufacturing requirements. In this thesis we investigate various aspects of this challenge. First, we consider polygon decomposition problems in the context of VLSI design rules. We introduce different width notions for polygons which are important for width-dependent design rules in VLSI routing, and we present efficient algorithms for computing width-preserving decompositions of rectilinear polygons into rectangles. Such decompositions are used in routing to allow for fast design rule checking. A main contribution of this thesis is an O(n) time algorithm for computing a decomposition of a simple rectilinear polygon with n vertices into O(n) rectangles, preseverving two-dimensional width. Here the two-dimensional width at a point of the polygon is defined as the edge length of a largest square that contains the point and is contained in the polygon. In order to obtain these results we establish a connection between such decompositions and Voronoi diagrams. Furthermore, we consider implications of multiple patterning and other advanced design rules for VLSI routing. The main contribution in this context is the detailed description of a routing approach which is able to manage such advanced design rules. As a main algorithmic concept we use multi-label shortest paths where certain path properties (which model design rules) can be enforced by defining labels assigned to path vertices and allowing only certain label transitions. The described approach has been implemented in BonnRoute, a VLSI routing tool developed at the Research Institute for Discrete Mathematics, University of Bonn, in cooperation with IBM. We present experimental results confirming that a flow combining BonnRoute and an external cleanup step produces far superior results compared to an industry standard router. In particular, our proposed flow runs more than twice as fast, reduces the via count by more than 20%, the wiring length by more than 10%, and the number of remaining design rule errors by more than 60%. These results obtained by applying our multiple patterning approach to real-world chip instances provided by IBM are another main contribution of this thesis. We note that IBM uses our proposed combined BonnRoute flow as the default tool for signal routing

Using an anisotropic diffusion scale-space for the detection and delineation of shacks in informal settlement imagery

PhD, Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2010Informal settlements are a growing world-wide phenomenon. Up-to-date spatial information mapping settlements is essential for a variety of end-user applications from planning settlement upgrading to monitoring expansion and infill. One method of gathering this information is through the analysis of nadir-view aerial imagery and the automated or semi-automated extraction of individual shacks. The problem of shack detection and delineation in, particularly South African, informal settlements is a unique and difficult one. This is primarily due to the inhomogeneous appearance of shack roofs, which are constructed from a variety of disparate materials, and the density of shacks. Previous research has focused mostly on the use of height data in conjunction with optical images to perform automated or semi-automated shack extraction. In this thesis, a novel approach to automating shack extraction is presented and prototyped, in which the appearance of shack roofs is homogenised, facilitating their detection. The main features of this strategy are: construction of an anisotropic scale-space from a single source image and detection of hypotheses at multiple scales; simplification of hypotheses' boundaries through discrete curve evolution and regularisation of boundaries in accordance with an assumed shack model - a 4-6 sided, compact, rectilinear shape; selection of hypotheses competing across scales using fuzzy rules; grouping of hypotheses based on their support for one another, and localisation and re-regularisation of boundaries through the incorporation of image edges. The prototype's performance is evaluated in terms of standard metrics and is analysed for four different images, having three different sets of imaging conditions, and containing well over a hundred shacks. Detection rates in terms of building counts vary from 83% to 100% and, in terms of roof area coverage, from 55% to 84%. These results, each derived from a single source image, compare favourably with those of existing shack detection systems, especially automated ones which make use of richer source data. Integrating this scale-space approach with height data offers the promise of even better results

Voronoi diagram of orthogonal polyhedra in two and three dimensions

Τα διαγράμματα Voronoi αποτελούν μία θεμελιώδη γεωμετρική δομή δεδομένων και έκφραζουν αποστάσεις σημείων στο χώρο από ένα σύνολο αντικειμένων. Θεωρούμε ορθογώνια πολύεδρα ευθυγραμμισμένα με τους άξονες. Πρόκειται για πολύεδρα των οποίων οι έδρες σχηματίζουν ορθές γωνίες, και οι ακμές είναι παράλληλες προς τους άξονες ενός καρτεσιανού συστήματος συντεταγμένων. Κατασκευάζουμε το διάγραμμα Voronoi στο εσωτερικό ενός ορθογώνιου πολυέδρου με τρύπες που ορίζονται από αντίστοιχα πολύεδρα, χρησιμοποιώντας την max-νόρμα. Πρόκειται για έναν συνδυασμό που βρίσκει πολλές εφαρμογές σε τομείς όπως τα raster graphics και ο σχεδιασμός κυκλωμάτων VLSI. Παρουσιάζουμε έναν αλγόριθμο για την κατασκευή αυτών των διαγραμμάτων Voronoi σε δύο και τρεις διαστάσεις. Ακολουθούμε τη μέθοδο υποδιαίρεσης και βασιζόμαστε σε μία δομή δεδομένων από bounding-volumes: πρόκειται για μία μή τετριμμένη προσέγγιση του προβλήματος. Επιπλέον αναλύουμε την πολυπλοκότητα του αλγορίθμου, η οποία είναι γραμμική κάτω από μία υπόθεση ομοιόμορφα κατανεμημένης εισόδου. Μέρος της παρούσας εργασίας πρόκειται να δημοσιευθεί στα πρακτικά του συνεδρίου SEA^2 2019 (Special Event on Analysis of Experimental Algorithms).Voronoi diagrams are a fundamental geometric data structure for obtaining proximity relations. We consider axis-aligned orthogonal polyhedra in two and three-dimensional space. These are polyhedra whose faces meet at right angles and their edges are aligned with the axes of a coordinate system. We construct the exact Voronoi diagram inside an axis-aligned orthogonal polyhedron with holes defined by such polyhedra, under the max-norm. This is a particularly useful scenario in certain application domains, including raster graphics and VLSI design. Our approach avoids creating full-dimensional elements on the Voronoi diagram and yields a skeletal representation of the input object, equivalent to the straight skeleton. We introduce a complete algorithm in 2D and 3D that follows the subdivision paradigm relying on a bounding-volume hierarchy; this is an original approach to the problem. The algorithm reads in a region bounding the input polyhedron and performs a recursive subdivision into cells (using quadtrees and octrees for 2D and 3D resp.). Then, a reconstruction technique is applied to produce an isomorphic representation of the Voronoi diagram. An hierarchical data structure of bounding volumes is used to accelerate the 2D algorithm for certain inputs and is necessary for the efficiency of the 3D algorithm. The complexity is adaptive and comparable to that of previous methods. Under a mild assumption it is O(n / D+1 / D^2) in 2D or O(n a ^2 / D^2+1 / D^3) in 3D, where n is the number of sites, namely edges or facets respectively, D is the maximum cell size for the subdivision to stop (and is <1 under the appropriate scaling), and a bounds vertex cardinality per facet. We also provide a numerically stable, open-source implementation in Julia, illustrating the practical nature of our algorithm. Part of the current thesis is given in the paper "Voronoi diagram of orthogonal polyhedra in two and three dimensions", co-authored with Prof. Ioannis Z. Emiris, that is about to appear in Proceedings of SEA^2 2019 (Special Event on Analysis of Experimental Algorithms)

Urban ground-based thermography

Urban climates are driven by micro-meteorological processes associated with the complex urban form, materials, and land cover patterns. Given its close link to the surface energy balance, surface temperature observations are key to the improvement and evaluation of models. This work contributes to the application of ground-based thermography in urban settings as an observational method to further our understanding of urban climate processes. In this thesis, ground-based thermography observations are collected and interpreted in a unique way so that they are relatable to scales used by urban climate models and earth observation (EO) satellites. At two measurement sites (simplified outdoor scale model and complex central urban setting), variations in surface temperature are quantitatively linked to micro-scale features such as shadow patterns and material characteristics at unprecedented levels of detail. Previous studies with low level of detail have inferred these properties. The detected upwelling longwave radiation is corrected to surface temperature (Ts) using a novel, high-resolution three-dimensional (3D) radiative transfer (RT) approach. From multi-day observational evaluation, the atmospheric correction has 0.39 K mean absolute error. Ground-based observations are combined with a comprehensive 3D radiative transfer model, enabling detailed simulation of EO land surface temperature (TsEO). For a mainly clear-sky summer day, TsEO at night underestimates the unbiased “complete” surface temperature (Tc) by 0.5 – 1 K, is similar to Tc during morning and evening, and for other times varies significantly with view angle (up to 5.1 K). Generally, view angle variation is smaller than prior studies as they typically use simpler geometry and temperature descriptions, and lack vegetation. Here, the observational basis and high-resolution modelling in a real central urban setting serves as a benchmark for future improvements of simplified model parameterisations

Sliceforms: Deployable structures from interlocking slices

A sliceform is a volumetric, honeycomb-like structure assembled from an array of cross-sectional planar slices that are interlocked via pairs of complementary slots placed along each intersection. If the slices are thin, these slotted intersections function as revolute joints, and the sliceform is foldable if the geometry of the embedded spatial linkage permits it, for example a lattice sliceform (LS) is bi-directionally flat-foldable. This thesis concerns a study of such sliceforms toward the design of novel deployable structures. A sliceform torus, composed of two sets of inclined slices arranged at regular intervals about a central axis of symmetry, has been discovered to exhibit a surprising and intriguing folding action whereby its incomplete form can be collapsed to a flat-folded stack of coplanar slices. On deployment, the assembly expands smoothly about an arc until the slices have rotated to their design inclination, then, without reaching any apparent physical limit, abruptly ‘locks out’. With a full complement of slices, the outermost intersections can be interlocked to complete and rigidify the ring. The torus is an example of a rotational sliceform (RS), and analysis of these structures proceeds by noting that their structural geometry comprises an array of pyramidal cells that is commensurate to a spherical scissor grid. The conditions for flat-foldability are determined by examination of the intrinsic geometry of each cell; the incompatibility of the slices with apparent rigid-folding revealed by assessment of the extrinsic motion of the slices. Investigation of their compliant kinematics reveals the articulation to be a bistable transition admitted by small transverse deflections of the slices. This structural form is generalised by development of a technique for generating sliceforms along a smooth spatial curve – curve sliceforms (CS). Their synthesis is more involved than for an RS, but a range of sliceform ‘tubes’ are generated and manufactured. Each example retains the flat-foldable, deployable characteristic of an RS, despite the apparent intrinsic rigidity of each constituent skew cell. Examination of the small-scale models indicates that deployable motion is achieved via imperfect action of the slots, and a simple model of the articulation of a single cell is constructed to investigate how this proceeds, verifying that motion is kinematically admissible via local deformations

Towards automatic modeling of buildings in informal settlements from aerial photographs using deformable active contour models (snakes)

Bibliography: leaves 177-187.This dissertation presents a novel system for semi-automatic modeling of buildings in informal settlement areas from aerial photographs. The building extraction strategy is developed and implememed with the aim of generatinga a desk top Informal Settlement Geographic lnformation System (ISGIS) using felf developed and available PC-based GIS tools to serve novice users informal settlement areas

Architectural Digital Photogrammetry

This study is to exploit texturing techniques of a common modelling software in the way of creating virtual models of an exist architectures using oriented panoramas. In this research, The panoramic image-based interactive modelling is introduced as assembly point of photography, topography, photogrammetry and modelling techniques. It is an interactive system for generating photorealistic, textured 3D models of architectural structures and urban scenes. The technique is suitable for the architectural survey because it is not a «point by point» survey, and it exploit the geometrical constraints in the architecture to simplify modelling. Many factors are presented to be critical features that affect the modelling quality and accuracy, such as the way and the position in shooting the photos, stitching the multi-image panorama photos, the orientation, texturing techniques and so on. During the last few years, many Image-based modelling programmes have been released. Whereas, in this research, the photo modelling programs was not in use, it meant to face the fundamentals of the photogrammetry and to go beyond the limitations of such software by avoiding the automatism. In addition, it meant to exploit the potent commands of a program as 3DsMax to obtain the final representation of the Architecture. Such representation can be used in different fields (from detailed architectural survey to an architectural representation in cinema and video games), considering the accuracy and the quality which they are vary too. After the theoretical studies of this technique, it was applied in four applications to different types of close range surveys. This practice allowed to comprehend the practical problems in the whole process (from photographing all the way to modelling) and to propose the methods in the ways to improve it and to avoid any complications. It was compared with the laser scanning to study the accuracy of this technique. Thus, it is realized that not only the accuracy of this technique is linked to the size of the surveyed object, but also the size changes the way in which the survey to be approached. Since the 3D modelling program is not dedicated to be used for the image-based modelling, texturing problems was faced. It was analyzed in: how the program can behave with the Bitmap, how to project it, how it could be an interactive projection, and what are the limitations

Large bichromatic point sets admit empty monochromatic 4-gons

We consider a variation of a problem stated by Erd˝os and Szekeres in 1935 about the existence of a number fES(k) such that any set S of at least fES(k) points in general position in the plane has a subset of k points that are the vertices of a convex k-gon. In our setting the points of S are colored, and we say that a (not necessarily convex) spanned polygon is monochromatic if all its vertices have the same color. Moreover, a polygon is called empty if it does not contain any points of S in its interior. We show that any bichromatic set of n ≥ 5044 points in R2 in general position determines at least one empty, monochromatic quadrilateral (and thus linearly many).Postprint (published version