Towards shape representation using trihedral mesh projections

This paper explores the possibility of approximating a surface by a trihedral polygonal mesh plus some triangles at strategic places. The presented approximation has attractive properties. It turns out that the Z-coordinates} of the vertices are completely governed by the Z-coordinates assigned to four selected ones. This allows describing the spatial polygonal mesh with just its 2D projection plus the heights of four vertices. As a consequence, these projections essentially capture the “spatial meaning” of the given surface, in the sense that, whatever spatial interpretations are drawn from them, they all exhibit essentially the same shape.This work was supported by the project 'Resolución de sistemas de ecuaciones cinemáticas para la simulación de mecanismos, posicionado interactivo de objetos y conformación de moléculas' (070-722).Peer Reviewe

Fast Mesh-based physical optics for large-scale electromagnetic analysis

Thesis (DPhil)--Stellenbosch University, 2016.ENGLISH ABSTRACT: At sufficiently high frequencies, the electrical size of scattering objects become very large. The electromagnetic field simulation of such objects becomes prohibitively expensive with physically rigorous (full wave) computational electromagnetics methods. In such cases, methods based on asymptotic assumptions can be employed instead, to approximately solve Maxwell’s equations. The physical optics (PO) approximation for a conducting surface, is a well-known asymptotic assumption. The multiple-reflection PO (MRPO) method is obtained by applying the PO approximation recursively, to model multiple reflections occurring internally to an object. The overall research goal of this work is to significantly accelerate the mesh-based MRPO for electromagnetic scattering analysis. A standard representation was chosen for the surface current, namely Rao- Wilton-Glisson (RWG) basis functions on a mesh of triangle elements. Since the MRPO is an extension of the single-reflection PO (SRPO), the main bottleneck in the SRPO, namely incident field shadowing determination, is addressed first. An adaptive, multilevel, buffer-based shadowing determination algorithm is developed which is robustly optimal, yielding O(N) time-scaling results for extreme test cases (N denotes the number of mesh elements). Secondly, the first ever, comprehensively accelerated version of the meshbased MRPO method (which rigorously takes internal shadowing into account), denoted fast MRPO (FMRPO), is developed. The FMRPO uses the multi-level, fast multipole method (MLFMM) to accelerate internal reflected field calculations. The inter-group interaction criterion of the MLFMM is altered to account for shadowing. Inter-group shadowing status flags are efficiently evaluated. The runtime scaling of the conventional MRPO is O(Nˆ2), while the runtime of the FMRPO scales as quasi-O(N log N), depending on the specific geometry. Results are presented for practical geometries with larger electrical sizes than have ever before been considered with the MRPO, but which can now for the first time be solved in realistically fast runtimes. With the FMRPO there is no fundamental limit to the electrical size of the scattering objects that can be solved.AFRIKAANSE OPSOMMING: By genoegsaam hoë frekwensies is die elektriese grootte van verstrooiingsvoorwerpe baie groot. Die elektromagnetiese veldsimulasie van sulke voorwerpe met fisies omvattende (volgolf) numeriese elektromagnetika metodes word dan te duur. In sulke gevalle kan metodes gebaseer op asimptotiese aannames eerder ingespan word, om Maxwell se vergelykings by benadering op te los. Die fisiese optika (FO) benadering vir ’n geleidende oppervlak is ’n welbekende asimptotiese aanname. Die multi-refleksie FO (MRFO) metode word verkry deur die FO benadering rekursief toe te pas, om veelvoudige refleksies te modelleer wat intern tot ’n voorwerp plaasvind. Die hoof navorsingsdoelwit van hierdie werk is om die maas-gebaseerde MRFO noemenswaardig te versnel vir elektromagnetiese verstrooiingsanalise. ’n Standaard voorstelling is gekies vir die oppervlaktestroomdigtheid, naamlik Rao-Wilton-Glisson (RWG) basisfunksies op ’n maas van driehoek elemente. Gegee dat MRFO ’n uitbreiding van enkel-refleksie FO (ERFO) is, word die hoof bottelnek van die ERFO, naamlik invallende-veld skaduweebepaling, eerste aangespreek. ’n Aanpassingsvaardige, multivlak, buffer-gebaseerde, skaduweebepalingsalgoritme is ontwikkel wat robuust optimaal is, met O(N) tydskaleringsresultate vir uiterste toetsgevalle (N verwys na die aantal maaselemente). Tweedens is die heel eerste, omvattend versnelde weergawe van die maas-gebaseerde MRFO metode (wat interne skaduwees streng in ag neem), genoem vinnige MRFO (VMRFO), ontwikkel. Die VMRFO inkorporeer die multivlak, vinnige multipool metode (MVVMM) om interne, weerkaatste veldberekeninge te versnel. Die intergroep interaksiekriterium van die MVVMM is aangepas om skaduwees in ag te neem. Intergroep skadustatusvlaggies word doeltreffend bepaal. Die berekeningstyd van die konvensionele MRFO skaleer as O(Nˆ2), terwyl die berekeningstyd van die VMRFO skaleer as kwasi-O(N log N), na gelang van die spesifieke geometrie. Resultate word getoon vir praktiese verstrooiingsvoorwerpe wat elektries groter is as wat ooit vantevore met die MRFO aangepak is, wat nou vir die eerste keer opgelos kan word in realisties vinnige berekeningstye. Met die VMRFO is daar geen fundamentele beperking op die elektriese grootte van die verstrooiingsvoorwerpe wat kan opgelos word nie

Motion Structures

Motion structures are simply assemblies of resistant bodies connected by movable joints. Unlike conventional structures, they allow large shape transformations to satisfy practical requirements and they can be used in:shelters, emergency structures and exhibition standsaircraft morphing wingssatellite solar panels and space antennasmorphing core m

Design and application of microstrip leaky wave antennas for radar sensing

textThis dissertation investigates the application of the frequency-scanned beam of a microstrip leaky wave antenna (LWA) to track humans in the two-dimensional (2-D) range-azimuth plane. The history, operating principles and frequency-scanned properties of a microstrip LWA are first reviewed. The basic concept of using a microstrip LWA to track humans is verified by designing, building and testing a broadband microstrip LWA, developing the necessary processing algorithm, and collecting data using a vector network analyzer. A number of topics are then investigated to further advance the concept. First, the idea of combining the frequency-scanned antenna with a short-pulse ultra-wideband (UWB) radar is developed to realize a portable, real-time system for human tracking. The radar concept and the components of the system are discussed in detail. Line-of-sight and through-wall measurements of a human subject are carried out to demonstrate the performance. Second, a new LWA structure is proposed to achieve a narrower azimuth beam, which requires both a small leaky-wave attenuation constant and a long aperture. The transverse resonance method (TRM) is applied to analyze the proposed structure and the results are verified with measurements of a built prototype. Third, a new signal processing technique, compressive sensing, is applied to further improve the resolution in both the azimuth and down range dimensions. The technique is tested with simulation and measurement data and is shown to produce sharper target responses in both the down range and azimuth dimensions. Lastly, the radar cross-section (RCS) of a microstrip LWA is studied. The antenna mode scattering and structural mode scattering are modeled separately. A ray picture is provided to explain the observed time-domain features using the group delay of the leaky wave.Electrical and Computer Engineerin

Motion Structures

Motion structures are simply assemblies of resistant bodies connected by movable joints. Unlike conventional structures, they allow large shape transformations to satisfy practical requirements and they can be used in:shelters, emergency structures and exhibition standsaircraft morphing wingssatellite solar panels and space antennasmorphing core m

Modeling 3D objects with free-form surfaces using 2D sketches

Ankara : The Department of Computer Engineering and the Graduate School of Engineering and Science, Bilkent University, 2011.Thesis (Master's) -- Bilkent University, 2011.Includes bibliographical refences.Using sketches for 3D modelling is a popular research area, which is expected since using 2D sketches feels natural to most of the artists. Many techniques have been proposed to enable an intuitive and competent tool for 3D object creation. In the light of the previous research in this area, we designed a system that enables creation of 3D free-form objects with details. Our system aims to enable users to easily create simple free-form objects using strokes and perturb their surfaces using sketches that provide contours of details and shading information. We provide the user with the ability to create a 3D simple object just by drawing its silhouette. We take this stroke input and create a simple 3D object. Then we allow the user to shade the parts of the 2D silhouette drawn before. We take the shading information and use shape from shading techniques to create a height map and apply the height map on the surface of the object to construct a perturbed surface for the previously created mesh. With our system, it is possible to create and modify 3D meshes easily and intuitively.Akatürk, EmreM.S

Applying image processing techniques to pose estimation and view synthesis.

Fung Yiu-fai Phineas.Thesis (M.Phil.)--Chinese University of Hong Kong, 1999.Includes bibliographical references (leaves 142-148).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Model-based Pose Estimation --- p.3Chapter 1.1.1 --- Application - 3D Motion Tracking --- p.4Chapter 1.2 --- Image-based View Synthesis --- p.4Chapter 1.3 --- Thesis Contribution --- p.7Chapter 1.4 --- Thesis Outline --- p.8Chapter 2 --- General Background --- p.9Chapter 2.1 --- Notations --- p.9Chapter 2.2 --- Camera Models --- p.10Chapter 2.2.1 --- Generic Camera Model --- p.10Chapter 2.2.2 --- Full-perspective Camera Model --- p.11Chapter 2.2.3 --- Affine Camera Model --- p.12Chapter 2.2.4 --- Weak-perspective Camera Model --- p.13Chapter 2.2.5 --- Paraperspective Camera Model --- p.14Chapter 2.3 --- Model-based Motion Analysis --- p.15Chapter 2.3.1 --- Point Correspondences --- p.16Chapter 2.3.2 --- Line Correspondences --- p.18Chapter 2.3.3 --- Angle Correspondences --- p.19Chapter 2.4 --- Panoramic Representation --- p.20Chapter 2.4.1 --- Static Mosaic --- p.21Chapter 2.4.2 --- Dynamic Mosaic --- p.22Chapter 2.4.3 --- Temporal Pyramid --- p.23Chapter 2.4.4 --- Spatial Pyramid --- p.23Chapter 2.5 --- Image Pre-processing --- p.24Chapter 2.5.1 --- Feature Extraction --- p.24Chapter 2.5.2 --- Spatial Filtering --- p.27Chapter 2.5.3 --- Local Enhancement --- p.31Chapter 2.5.4 --- Dynamic Range Stretching or Compression --- p.32Chapter 2.5.5 --- YIQ Color Model --- p.33Chapter 3 --- Model-based Pose Estimation --- p.35Chapter 3.1 --- Previous Work --- p.35Chapter 3.1.1 --- Estimation from Established Correspondences --- p.36Chapter 3.1.2 --- Direct Estimation from Image Intensities --- p.49Chapter 3.1.3 --- Perspective-3-Point Problem --- p.51Chapter 3.2 --- Our Iterative P3P Algorithm --- p.58Chapter 3.2.1 --- Gauss-Newton Method --- p.60Chapter 3.2.2 --- Dealing with Ambiguity --- p.61Chapter 3.2.3 --- 3D-to-3D Motion Estimation --- p.66Chapter 3.3 --- Experimental Results --- p.68Chapter 3.3.1 --- Synthetic Data --- p.68Chapter 3.3.2 --- Real Images --- p.72Chapter 3.4 --- Discussions --- p.73Chapter 4 --- Panoramic View Analysis --- p.76Chapter 4.1 --- Advanced Mosaic Representation --- p.76Chapter 4.1.1 --- Frame Alignment Policy --- p.77Chapter 4.1.2 --- Multi-resolution Representation --- p.77Chapter 4.1.3 --- Parallax-based Representation --- p.78Chapter 4.1.4 --- Multiple Moving Objects --- p.79Chapter 4.1.5 --- Layers and Tiles --- p.79Chapter 4.2 --- Panorama Construction --- p.79Chapter 4.2.1 --- Image Acquisition --- p.80Chapter 4.2.2 --- Image Alignment --- p.82Chapter 4.2.3 --- Image Integration --- p.88Chapter 4.2.4 --- Significant Residual Estimation --- p.89Chapter 4.3 --- Advanced Alignment Algorithms --- p.90Chapter 4.3.1 --- Patch-based Alignment --- p.91Chapter 4.3.2 --- Global Alignment (Block Adjustment) --- p.92Chapter 4.3.3 --- Local Alignment (Deghosting) --- p.93Chapter 4.4 --- Mosaic Application --- p.94Chapter 4.4.1 --- Visualization Tool --- p.94Chapter 4.4.2 --- Video Manipulation --- p.95Chapter 4.5 --- Experimental Results --- p.96Chapter 5 --- Panoramic Walkthrough --- p.99Chapter 5.1 --- Problem Statement and Notations --- p.100Chapter 5.2 --- Previous Work --- p.101Chapter 5.2.1 --- 3D Modeling and Rendering --- p.102Chapter 5.2.2 --- Branching Movies --- p.103Chapter 5.2.3 --- Texture Window Scaling --- p.104Chapter 5.2.4 --- Problems with Simple Texture Window Scaling --- p.105Chapter 5.3 --- Our Walkthrough Approach --- p.106Chapter 5.3.1 --- Cylindrical Projection onto Image Plane --- p.106Chapter 5.3.2 --- Generating Intermediate Frames --- p.108Chapter 5.3.3 --- Occlusion Handling --- p.114Chapter 5.4 --- Experimental Results --- p.116Chapter 5.5 --- Discussions --- p.116Chapter 6 --- Conclusion --- p.121Chapter A --- Formulation of Fischler and Bolles' Method for P3P Problems --- p.123Chapter B --- Derivation of z1 and z3 in terms of z2 --- p.127Chapter C --- Derivation of e1 and e2 --- p.129Chapter D --- Derivation of the Update Rule for Gauss-Newton Method --- p.130Chapter E --- Proof of (λ1λ2-λ 4）>〉0 --- p.132Chapter F --- Derivation of φ and hi --- p.133Chapter G --- Derivation of w1j to w4j --- p.134Chapter H --- More Experimental Results on Panoramic Stitching Algorithms --- p.138Bibliography --- p.14