Dissertations / Theses on the topic 'Geometrical calibration'

In the fringe-illumination deflectometry based on reverse-Hartmann-test configuration, ray tracing of the modeled testing system is performed to reconstruct the test surface error. Careful calibration of system geometry is required to achieve high testing accuracy. To realize the high-precision surface testing with reverse Hartmann test, a computer-aided geometrical error calibration method is proposed. The aberrations corresponding to various geometrical errors are studied. With the aberration weights for various geometrical errors, the computer-aided optimization of system geometry with iterative ray tracing is carried out to calibration the geometrical error, and the accuracy in the order of sub-nanometer is achieved.

Tato dizertace je zaměřena na medicínskou zobrazovací modalitu – ultrazvukovou počítačovou tomografii – a algoritmy zlepšující kvalitu zobrazení, zejména kalibraci USCT přístroje. USCT je novou modalitou kombinující ultrazvukový přenos signálů a principy tomografické rekonstrukce obrazů vyvíjených pro jiné tomografické systémy. V principu lze vytvořit kvantitativní 3D obrazové objemy s vysokým rozlišením a kontrastem. USCT je primárně určeno pro diagnózu rakoviny prsu. Autor spolupracoval na projektu Institutu Zpracování dat a Elektroniky, Forschungszentrum Karlsruhe, kde je USCT systém vyvíjen. Jeden ze zásadních problémů prototypu USCT v Karlsruhe byla absence kalibrace. Tisíce ultrazvukových měničů se liší v citlivosti, směrovosti a frekvenční odezvě. Tyto parametry jsou navíc proměnné v čase. Další a mnohem závažnější problém byl v pozičních odchylkách jednotlivých měničů. Všechny tyto aspekty mají vliv na konečnou kvalitu rekonstruovaných obrazů. Problém kalibrace si autor zvolil jako hlavní téma dizertace. Tato dizertace popisuje nové metody v oblastech rekonstrukce útlumových obrazů, kalibrace citlivosti měničů a zejména geometrická kalibrace pozic měničů. Tyto metody byly implementovány a otestovány na reálných datech pocházejících z prototypu USCT z Karlsruhe.

The aim of this work is description of a device developed at Brno University of Technology, Faculty of Civil Engineering, Institute of Geodesy for the purpose of absolute calibration of geodetic GNSS antennas. Thanks to calibration it is possible to remove systematic error of antenna's phase centre. The device consists of moveable arm and processing unit. The moveable arm is able to set up calibrated antenna to required azimuth and elevation angle. This work introduces the issue of absolute calibration, describes the moveable arm and the process of its assembling. Further, it defines geometrical parameters of moveable arm, describes their determination and their independent verification by geodetic method. Finally, the model of movement of antenna's reference point is described.

A multiple-sensor optical shape measurement system (SMS) based on the principle of white-light fringe projection has been developed and commercialised by Loughborough University and Phase Vision Ltd for over 10 years. The use of the temporal phase unwrapping technique allows precise and dense shape measurements of complex surfaces; and the photogrammetry-based calibration technique offers the ability to calibrate multiple sensors simultaneously in order to achieve 360° measurement coverage. Nevertheless, to enhance the applicability of the SMS in industrial environments, further developments are needed (i) to improve the calibration speed for quicker deployment, (ii) to broaden the application range from shape measurement to deformation field measurement, and (iii) to tackle practically-challenging surfaces of which specular components may disrupt the acquired data and result in spurious measurements. The calibration process typically requires manual positioning of an artefact (i.e., reference object) at many locations within the view of the sensors. This is not only timeconsuming but also complicated for an operator with average knowledge of metrology. This thesis introduces an automated artefact positioning system which enables automatic and optimised distribution of the artefacts, automatic prediction of their whereabouts to increase the artefact detection speed and robustness, and thereby greater overall calibration performance. This thesis also describes a novel technique that integrates the digital image correlation (DIC) technique into the present fringe projection SMS for the purpose of simultaneous shape and deformation field measurement. This combined technique offers three key advantages: (a) the ability to deal with geometrical discontinuities which are commonly present on mechanical surfaces and currently challenging to most deformation measurement methods, (b) the ability to measure 3D displacement fields with a basic single-camera single-projector SMS with no additional hardware components, and (c) the simple implementation on a multiple-sensor hardware platform to achieve complete coverage of large-scale and complex samples, with the resulting displacement fields automatically lying in a single global coordinate system. A displacement measurement accuracy of ≃ 1/12,000 of the measurement volume, which is comparable to that of an industry-standard DIC system, has been achieved. The applications of this novel technique to several structural tests of aircraft wing panels on-site at the research centre of Airbus UK in Filton are also presented. Mechanical components with shiny surface finish and complex geometry may introduce another challenge to present fringe projection techniques. In certain circumstances, multiple reflections of the projected fringes on an object surface may cause ambiguity in the phase estimation process and result in incorrect coordinate measurements. This thesis presents a new technique which adopts a Fourier domain ranging (FDR) method to correctly identifying multiple phase signals and enables unambiguous triangulation for a measured coordinate. Experiments of the new FDR technique on various types of surfaces have shown promising results as compared to the traditional phase unwrapping techniques.

A novel lidar ceilometer prototype based on divided lens optics has been designed, built, characterised, and tested. The primary applications for this manufacturable ground-based sensor are the determination of cloud base height and the measurement of vertical visibility. First, the design, which was developed in order to achieve superior performance at a low cost, is described in detail, along with the process used to develop it. The primary design considerations of optical signal to noise ratio, range-dependent overlap of the transmitter and receiver channels, and manufacturability, were balanced to develop an instrument with good signal to noise ratio, fast turn-on of overlap for detection of close range returns, and a minimised number of optical components and simplicity of assembly for cost control purposes. Second, a novel imaging method for characterisation of transmitter-receiver overlap as a function of range is described and applied to the instrument. The method is validated by an alternative experimental method and a geometric calculation that is specific to the unique geometry of the instrument. These techniques allow the calibration of close range detection sensitivity in order to acquire information prior to full overlap. Finally, signal processing methods used to automate the detection process are described. A novel two-part cloud base detection algorithm has been developed which combines extinction-derived visibility thresholds in the inverted cloud return signal with feature detection on the raw signal. In addition, standard approaches for determination of visibility based on an iterative far boundary inversion method, and calibration of attenuated backscatter profile using returns from a fully-attenuating water cloud, have been applied to the prototype. The prototype design, characterisation, and signal processing have been shown to be appropriate for implementation into a commercial instrument. The work that has been carried out provides a platform upon which a wide range of further work can be built.

Robot tasks are becoming more complex, as they can now be coded off-line by integrating the robot mathematical model into the controller. One of the main technological barriers in the robotics industry has been the reduction of discrepancies between the robot mathematical model and the actual robot geometry, by means of a process called geometric calibration. In this work, an inexpensive, time-effective and versatile closed-loop calibration method for serial robots is introduced. Contrary to most calibration methods, the proposed method does not require any external measurement system. The main idea is to fix the end-effector of a seven-degree-of-freedom 3D kinematic chain, formed with the robot joints and, if required, additional passive joints. Then, while performing a self-motion, i.e. changing the posture of the chain without changing its last link pose, the robot joint positions are recorded. Finally, the last link pose, computed using the mathematical model of the chain for the different postures, is subtracted from all others, thereby resulting in an overdetermined non-linear system of equations, from which the robot geometric parameters can be found. Two parameter representations were first chosen and applied to the CUATRO Arm, a serial four-degree-of-freedom redundant positioning robot, and the Thermo CRS A465, a seven-degree-of-freedom industrial robot. A versatile calibration set-up was then designed and manufactured to fix the end-effector of these robots. Moreover, different numerical identification methods were proposed and tested by means of simulation. Finally, the calibration method adopted here was applied to the CUATRO Arm and the Thermo CRS A465 robot. Although the experimental results correlated with the simulation results, the proposed calibration method was found to be highly sensitive to input noise.

To maximise productivity and reduce scrap in high-value, low-volume production, five-axis machine tool (5A-MT) motion accuracy must be verified quickly and reliably. Numerous metrology instruments have been developed to measure errors arising from geometric imperfections within and between machine tool axes (amongst other sources). One example is the TMBB, which is becoming an increasingly popular instrument to measure both linear and rotary axis errors. This research proposes new TMBB measurement technique to rapidly, accurately and reliably measure all position-independent rotary axis errors in a 5A-MT. In this research two literature reviews have been conducted. The findings informed the subsequent development of a virtual machine tool (VMT). This VMT was used to capture the effects of rotary and linear axis position-independent geometric errors, and apparatus set-up errors on a variety of candidate measurement routines. This new knowledge then informed the design of an experimental methodology to capture specific phenomena that were observed within the VMT on a commercial 5A-MT. Finally, statistical analysis of experimental measurements facilitated a quantification of the repeatability, strengths and limitations of the final testing method concept. The major contribution of this research is the development of a single set-up testing procedure to identify all 5A-MT rotary axis location errors, whilst remaining robust in the presence of set-up and linear axis location errors. Additionally, a novel variance-based sensitivity analysis approach was used to design testing procedures. By considering the effects of extraneous error sources (set-up and linear location) in the design and validation phases, an added robustness was introduced. Furthermore, this research marks the first usage of Monte Carlo uncertainty analysis in conjunction with rotary axis TMBB testing. Experimental evidence has shown that the proposed corrections for set-up and linear axis errors are highly effective and completely indispensable in rotary axis testing of this kind. However, further development of the single set-up method is necessary, as geometric errors cannot always be measured identically at different testing locations. This has highlighted the importance of considering the influences on 5A-MT component errors on testing results, as the machine tool axes cannot necessarily be modelled as straight lines.

Une des conditions fondamentales de la performance des système repose sur leur capacité à généré des déplacement avec précision de positionnement élevée. Cependant, à l'échelle micrométrique, de nombreux paramètres agissent et réduisent cette précision. A cette échelle, il est également particulièrement complexe de mesurer la précision de positionnement d'un système micro ou nanorobotique et donc d'identifier les différentes sources d'imprécision. L'étalonnage géométrique des systèmes micro et nanorobotiques prenant en compte ces différents sources est rarement étudié. Pour ces raisons, l'originalité et les contribution de cette thèse portent sur deux aspects principaux (i) la caractérisation des perperformances des systèmes micro et nanorobotiques et l'analyse des paramètres affectant leur précision de positionnement (ii) l'amélioration des performances de ces robots fondés sur différents types de modèles robotiques.

Abstract Automatic three-dimensional scene reconstruction from multiple images is a central problem in geometric computer vision. This thesis considers topics that are related to this problem area. New models and methods are presented for various tasks in such specific domains as camera calibration, image-based modeling and image matching. In particular, the main themes of the thesis are geometric camera calibration and quasi-dense image matching. In addition, a topic related to the estimation of two-view geometric relations is studied, namely, the computation of a planar homography from corresponding conics. Further, as an example of a reconstruction system, a structure-from-motion approach is presented for modeling sewer pipes from video sequences. In geometric camera calibration, the thesis concentrates on central cameras. A generic camera model and a plane-based camera calibration method are presented. The experiments with various real cameras show that the proposed calibration approach is applicable for conventional perspective cameras as well as for many omnidirectional cameras, such as fish-eye lens cameras. In addition, a method is presented for the self-calibration of radially symmetric central cameras from two-view point correspondences. In image matching, the thesis proposes a method for obtaining quasi-dense pixel matches between two wide baseline images. The method extends the match propagation algorithm to the wide baseline setting by using an affine model for the local geometric transformations between the images. Further, two adaptive propagation strategies are presented, where local texture properties are used for adjusting the local transformation estimates during the propagation. These extensions make the quasi-dense approach applicable for both rigid and non-rigid wide baseline matching. In this thesis, quasi-dense matching is additionally applied for piecewise image registration problems which are encountered in specific object recognition and motion segmentation. The proposed object recognition approach is based on grouping the quasi-dense matches between the model and test images into geometrically consistent groups, which are supposed to represent individual objects, whereafter the number and quality of grouped matches are used as recognition criteria. Finally, the proposed approach for dense two-view motion segmentation is built on a layer-based segmentation framework which utilizes grouped quasi-dense matches for initializing the motion layers, and is applicable under wide baseline conditions.

The thesis deals with the optimal pose selection for geometric and elastostatic calibration for industrial robots employed in machining of large parts. Particular attention is paid to the improvement of robot positioning accuracy after compensation of the geometric and elastostatic errors. To meet the industrial requirements of machining operations, a new approach for calibration experiments design for serial and quasi-serial industrial robots is proposed. This approach is based on a new industry-oriented performance measure that evaluates the quality of calibration experiment plan via the manipulator positioning accuracy after error compensation, and takes into account the particularities of prescribed manufacturing task by introducing manipulator test-poses. Contrary to previous works, the developed approach employs an enhanced partial pose measurement method, which uses only direct position measurements from an external device and allows us to avoid the non-homogeneity of relevant identification equations. In order to consider the impact of gravity compensator that creates closed-loop chains, the conventional stiffness model is extended by including in it some configuration dependent elastostatic parameters, which are assumed to be constant for strictly serial robots. Corresponding methodology for calibration of the gravity compensator models is also proposed. The advantages of the developed calibration techniques are validated via experimental study, which deals with geometric and elastostatic calibration of a KUKA KR-270 industrial robot.

The cone-beam flat panel micro-CT is a high definition imaging system. It acquires projections of an object or animal to reconstruct a 3D image of its internal structure. The device is basically composed by a radiation tube and a detector panel, which are fixed to a gantry that rotates all around the test subject. The micro-CT system is affected by several imperfections and problems, that might lead to serious artifacts that deteriorate the quality of the reconstructed image. In particular, two issues have been discussed in the present work: the source-panel geometric misalignment and the detector lag effect. The first problem concerns the consequences of systems where the different elements are not perfectly aligned to each other. The second issue regards the residual signal, left in the detector's sensor after a projection acquisition, which affects the following frames with ghost images. Both these arguments have been investigated to describe their characteristics and behaviour in a typical acquisition protocol. Then two correction methods have been presented and tested on a real micro-CT device to verify their effectiveness in the artifacts compensation. In the end, a comparison between images before and after the corrections is provided and future prospects are discussed.

Um dos grandes desafios em medidas de espectrometria gama utilizando fontes que não podem ser consideradas pontuais é a determinação da eficiência de detecção do sistema, uma vez que a geometria da fonte impõe complexidades na tarefa como o tratamento do ângulo sólido e da auto-absorção. Alguns métodos para o cálculo dessa eficiência já são bem estabelecidos e podem ser encontrados na literatura. Neste trabalho é proposto um método com características distintas aos já existentes cujas principais vantagens são, não depender de conhecimento prévio da geometria de detecção e da composição química da amostra a ser medida, e permitir o cálculo da eficiência de uma fonte extensa a partir de medidas com fontes padrão em formato pontual. O método proposto foi testado comparando os valores das eficiências obtidas por ele com os valores obtidos usando uma fonte padrão extensa. Para testar o método proposto em diferentes condições foi utilizado solo como matriz para a amostra em duas diferentes espessuras, 1cm e 3cm. Testou-se também o comportamento do método quando a matriz tem número atômico efetivo mais alto (aqui utilizou-se solo misturado à limalha de ferro) e mais baixo (adição de pó de grafite ao solo). Os resultados indicaram que o método é adequado para amostras de solo com espessura mais fina; já para fontes mais espessas, dois dos três resultados indicaram que a eficiência foi subestimada pelo método proposto, sugerindo que uma geometria mais adequada deva ser escolhida para a amostragem das medidas
One of the greatest challenges in gamma spectroscopy measurements using extense sources is the determination of the system\'s detection efficiency, since the source\'s geometry leads to added complexity to the treatment of parameters as geometry and self-absorption. Some well-established methods for the efficiency determination can be found in the literature. In the present work a method with distinct characteristics is proposed with the main advantages that it doesn\'t require previous knowledge of the detection geometry or of the sample composition; moreover, it allows the determination of the detection efficiency for a large sample based only on measurements using a point-like standard source. The proposed method was tested comparing the efficiency values obtained using the method with the values obtained using a real large source with the same composition and geometry. In order to verify the performance of the method under different conditions, soil matrixes of two different thicknesses (1cm and 3cm) were used; also, to asses the method under different sample compositions, 3cm-thick soil matrixes with increased effective atomic number (where iron filings was added) and with reduced effective atomic mass (where graphite powder was added) were used. The results indicate that the proposed method is suitable for thinner soil samples; as for thicker samples, two of the three results showed a subestimation of the detection efficiency value determined, suggesting that a more suitable sampling geometry should be analyzed.

L'apparition récente de microphones numériques MEMS a ouvert de nouvelles perspectives pour le développement de systèmes d'acquisition acoustiques massivement multi-canaux de grande envergure. De tels systèmes permettent de localiser des sources acoustiques avec de bonnes performances. En revanche, de nouvelles contraintes se posent. La première est le flux élevé de données issues de l'antenne, devant être traitées en un temps raisonnable. La deuxième contrainte est de connaître la position des nombreux microphones déployés in situ. Ce manuscrit propose des méthodes répondant à ces deux contraintes. Premièrement, une étude du système d'acquisition est présentée. On montre que les microphones MEMS sont adaptés pour des applications d'antennerie. Ensuite, un traitement en temps réel des signaux acquis via une implémentation parallèle sur GPU est proposé. Cette stratégie répond au problème de flux de données. On dispose ainsi d'un outil d'imagerie temps réel de sources large bande, permettant d'établir un diagnostic dynamique de la scène sonore.Deuxièmement, différentes méthodes de calibration géométrique pour la détermination de la position des microphones sont exposées. Dans des conditions réelles d'utilisation, les méthodes actuelles sont inefficaces pour des antennes étendues et à grand nombre de microphones. Ce manuscrit propose des techniques privilégiant la robustesse du processus de calibration. Les méthodes proposées couvrent différents environnements acoustiques réels, du champ libre au champ réverbérant. Leur efficacité est prouvée par différentes campagnes expérimentales
Recently, digital MEMS microphones came out and have opened new perspectives. One of them is the design of large-aperture and massively multichannel acoustical acquisition systems. Such systems meet good requirements for efficient source localization. However, new problems arise. First, an important data flow comes from the array, and must be processed fast enough. Second, if the large array is set up in situ, retrieving the position of numerous microphones becomes a challenging task. This thesis proposes methods addressing these two problems. The first part exhibits the description of the acquisition system, which has been developed during the thesis. First, we show that MEMS microphone characteristics are suitable for array processing applications. Then, real-time processing of channel signals is achieved by a parallel GPU implementation. This strategy is one solution to the heavy data flow processing issue. In this way, a real-time acoustic imaging tool was developed, and enables a dynamic wide-band diagnosis, for an arbitrary duration.The second part presents several robust geometric calibration methods: they retrieve microphone positions, based only on the array acoustic signals. Indeed, in real-life conditions, the state of the art methods are inefficient with large arrays. This thesis proposes techniques that guarantee the robustness of the calibration process. The proposed methods allow calibration in the different existing soundscapes, from free field to reverberant field. Various experimental scenarios prove the efficiency of the methods

Road safety is one of the most important problems in our society. It causes hundreds of fatalities every year worldwide. A road accident may be caused by several concurrent factors. The most common are human and infrastructure. Their interaction is important too, which has been studied in-depth for years. Therefore, there is a better knowledge about the driving task. In several cases, these advances are still not included in road guidelines. Some of these advances are centered on explaining the underlying cognitive processes of the driving task. Some others are related to the analysis of drivers’ response or a better estimation of road crashes. The concept of design consistency is related to all of them. Road design consistency is the way how road alignment fits drivers’ expectancies. Hence, drivers are surprised at inconsistent roads, presenting a higher crash risk potential. This PhD presents a new, operating speed-based global consistency model. It is based on the analysis of more than 150 two-lane rural homogeneous road segments of the Valencian Region (Spain). The final consistency parameter was selected as the combination of operational parameters that best estimated the number of crashes. Several innovative auxiliary tools were developed for this process. One example is a new tool for recreating the horizontal alignment of two-lane rural roads by means of an analytic-heuristic process. A new procedure for determining road homogeneous segments was also developed, as well as some expressions to accurately determine the most adequate design speed. The consistency model can be integrated into safety performance functions in order to estimate the amount of road crashes. Finally, all innovations are combined into a new road design methodology. This methodology aims to complement the existing guidelines, providing to road safety a continuum approach and giving the engineers tools to estimate how safe are their road designs.
Camacho Torregrosa, FJ. (2015). DEVELOPMENT AND CALIBRATION OF A GLOBAL GEOMETRIC DESIGN CONSISTENCY MODEL FOR TWO-LANE RURAL HIGHWAYS, BASED ON THE USE OF CONTINUOUS OPERATING SPEED PROFILES [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48543
TESIS

Unmanned aerial vehicles (UAV) have become an interesting and active research topic for photogrammetry. Current research is based on images acquired by an UAV, which have a high ground resolution and good spectral and radiometrical resolution, due to the low flight altitudes combined with a high resolution camera. UAV image flights are also cost effective and have become attractive for many applications including, change detection in small scale areas. One of the main problems preventing full automation of data processing of UAV imagery is the degradation effect of blur caused by camera movement during image acquisition. This can be caused by the normal flight movement of the UAV as well as strong winds, turbulence or sudden operator inputs. This blur disturbs the visual analysis and interpretation of the data, causes errors and can degrade the accuracy in automatic photogrammetric processing algorithms. The detection and removal of these images is currently achieved manually, which is both time consuming and prone to error, particularly for large image-sets. To increase the quality of data processing an automated process is necessary, which must be both reliable and quick. This thesis proves the negative affect that blurred images have on photogrammetric processing. It shows that small amounts of blur do have serious impacts on target detection and that it slows down processing speed due to the requirement of human intervention. Larger blur can make an image completely unusable and needs to be excluded from processing. To exclude images out of large image datasets an algorithm was developed. The newly developed method makes it possible to detect blur caused by linear camera displacement. The method is based on human detection of blur. Humans detect blurred images best by comparing it to other images in order to establish whether an image is blurred or not. The developed algorithm simulates this procedure by creating an image for comparison using image processing. Creating internally a comparable image makes the method independent of additional images. However, the calculated blur value named SIEDS (saturation image edge difference standard-deviation) on its own does not provide an absolute number to judge if an image is blurred or not. To achieve a reliable judgement of image sharpness the SIEDS value has to be compared to other SIEDS values of the same dataset. This algorithm enables the exclusion of blurred images and subsequently allows photogrammetric processing without them. However, it is also possible to use deblurring techniques to restor blurred images. Deblurring of images is a widely researched topic and often based on the Wiener or Richardson-Lucy deconvolution, which require precise knowledge of both the blur path and extent. Even with knowledge about the blur kernel, the correction causes errors such as ringing, and the deblurred image appears muddy and not completely sharp. In the study reported in this paper, overlapping images are used to support the deblurring process. An algorithm based on the Fourier transformation is presented. This works well in flat areas, but the need for geometrically correct sharp images for deblurring may limit the application. Another method to enhance the image is the unsharp mask method, which improves images significantly and makes photogrammetric processing more successful. However, deblurring of images needs to focus on geometric correct deblurring to assure geometric correct measurements. Furthermore, a novel edge shifting approach was developed which aims to do geometrically correct deblurring. The idea of edge shifting appears to be promising but requires more advanced programming.

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Um sistema câmera-projetor é capaz de capturar informação geométrica tridimensional de objetos e ambientes do mundo real. A captura de geometria em tal sistema baseia-se na projeção de luz estruturada sobre um objeto através do projetor, e na captura da cena modulada através da câmera. Com o sistema previamente calibrado, a deformação da luz projetada causada pelo objeto fornece a informação necessária para reconstruir a geometria do mesmo por meio de triangulação. Este trabalho descreve o desenvolvimento de um digitalizador câmera-projetor de alta definição (com resoluções de até 1920x1080 e 1280x720); são detalhadas as etapas e processos que conduzem à reconstrução de geometria, como calibração câmera-projetor, calibração de cores, processamento da imagem capturada e triangulação. O digitalizador desenvolvido utiliza a codificação de luz estruturada (b; s)-BCSL, que emprega a projeção de uma sequência de faixas verticais coloridas sobre a cena. Este esquema de codificação flexível oferece um número variado de faixas para projeção: quanto maior o número de faixas, mais detalhada a geometria capturada. Um dos objetivos deste trabalho é estimar o número limite de faixas (b,s)-BCSL possível dentro das resoluções atuais de vídeo de alta definição. Este número limite é aquele que provê reconstrução densa da geometria alvo, e ao mesmo tempo possui baixo nível de erro. Para avaliar a geometria reconstruída pelo digitalizador para os diversos números de faixas, é proposto um protocolo para avaliação de erro. O protocolo desenvolvido utiliza planos como objetos para mensurar a qualidade de reconstrução geométrica. A partir da nuvem de pontos gerada pelo digitalizador, a equação do plano para a mesma é estimada por meio de mínimos quadrados. Para um número fixo de faixas, são feitas cinco digitalizações independentes do plano: cada digitalização leva a uma equação; também é computado o plano médio, estimado a partir da união das cinco nuvens de pontos. Uma métrica de distância no espaço projetivo é usada para avaliar a precisão e a acurácia de cada número de faixas projetados. Além da avaliação quantitativa, a geometria de vários objetos é apresentada para uma avaliação qualitativa. Os resultados demonstram que a quantidade de faixas limite para vídeos de alta resolução permite uma grande densidade de pontos mesmo em superfícies com alta variação de cores.
A camera-projector system is capable of capturing three-dimensional geometric information of objects and real-world environments. The capture of geometry in such system is based on the projection of structured light over an object by the projector, and the capture of the modulated scene through the camera. With a calibrated system, the deformation of the projected light caused by the object provides the information needed to reconstruct its geometry through triangulation. The present work describes the development of a high definition camera-projector system (with resolutions up to 1920x1080 and 1280x720). The steps and processes that lead to the reconstruction of geometry, such as camera-projector calibration, color calibration, image processing and triangulation, are detailed. The developed scanner uses the (b; s)-BCSL structured light coding, which employs the projection of a sequence of colored vertical stripes on the scene. This coding scheme offers a flexible number of stripes for projection: the higher the number of stripes, more detailed is the captured geometry. One of the objectives of this work is to estimate the limit number of (b; s)-BCSL stripes possible within the current resolutions of high definition video. This limit number is the one that provides dense geometry reconstruction, and at the same has low error. To evaluate the geometry reconstructed by the scanner for a different number of stripes, we propose a protocol for error measurement. The developed protocol uses planes as objects to measure the quality of geometric reconstruction. From the point cloud generated by the scanner, the equation for the same plane is estimated by least squares. For a fixed number of stripes, five independent scans are made for the plane: each scan leads to one equation; the median plane, estimated from the union of the five clouds of points, is also computed. A distance metric in the projective space is used to evaluate the precision and the accuracy of each number of projected stripes. In addition to the quantitative evaluation, the geometry of many objects are presented for qualitative evaluation. The results show that the limit number of stripes for high resolution video allows high density of points even on surfaces with high color variation.

Orientador: Antonio Maria Garcia Tommaselli
Resumo: A combinação de duas lentes com FOV hiper-hemisférico em posição opostas pode gerar um sistema omnidirecional (FOV 360°) leve, compacto e de baixo custo, como Ricoh Theta S e GoPro Fusion. Entretanto, apenas algumas técnicas e modelos matemáticos para a calibração um sistema com duas lentes hiper-hemisféricas são apresentadas na literatura. Nesta pesquisa, é avaliado e definido um modelo geométrico para calibração de sistemas omnidirecionais compostos por duas lentes hiper-hemisféricas e apresenta-se algumas aplicações com esse tipo de sistema. A calibração das câmaras foi realizada no programa CMC (calibração de múltiplas câmeras) utilizando imagens obtidas a partir de vídeos feitos com a câmara Ricoh Theta S no campo de calibração 360°. A câmara Ricoh Theta S é composto por duas lentes hiper-hemisféricas fisheye que cobrem 190° cada uma. Com o objetivo de avaliar as melhorias na utilização de pontos em comum entre as imagens, dois conjuntos de dados de pontos foram considerados: (1) apenas pontos no campo hemisférico, e (2) pontos em todo o campo de imagem (isto é, adicionar pontos no campo de imagem hiper-hemisférica). Primeiramente, os modelos ângulo equisólido, equidistante, estereográfico e ortogonal combinados com o modelo de distorção Conrady-Brown foram testados para a calibração de um sensor da câmara Ricoh Theta S. Os modelos de ângulo-equisólido e estereográfico apresentaram resultados melhores do que os outros modelos. Portanto, esses dois modelos de projeção for... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The arrangement of two hyper-hemispherical fisheye lenses in opposite position can design a light weight, small and low-cost omnidirectional system (360° FOV), e.g. Ricoh Theta S and GoPro Fusion. However, only a few techniques are presented in the literature to calibrate a dual-fisheye system. In this research, a geometric model for dual-fisheye system calibration was evaluated, and some applications with this type of system are presented. The calibrating bundle adjustment was performed in CMC (calibration of multiple cameras) software by using the Ricoh Theta video frames of the 360° calibration field. The Ricoh Theta S system is composed of two hyper-hemispherical fisheye lenses with 190° FOV each one. In order to evaluate the improvement in applying points in the hyper-hemispherical image field, two data set of points were considered: (1) observations that are only in the hemispherical field, and (2) points in all image field, i.e. adding points in the hyper-hemispherical image field. First, one sensor of the Ricoh Theta S system was calibrated in a bundle adjustment based on the equidistant, equisolid-angle, stereographic and orthogonal models combined with Conrady-Brown distortion model. Results showed that the equisolid-angle and stereographic models can provide better solutions than those of the others projection models. Therefore, these two projection models were implemented in a simultaneous camera calibration, in which the both Ricoh Theta sensors were considered i... (Complete abstract click electronic access below)
Mestre

A camera calibration procedure corresponds to determine the digital geometric and optical characteristics of the camera from a known initial data set. This problem can be divided into three steps: a) acquisition of initial data; b) calibration process itself; and c) optimization. This work presents the development of a calibration tool based on a generic architecture for any calibration approach. For this aim, the presented system allows the personalization of each calibration step. In the proposed tool new calibration procedures are introduced dynamically, allowing a better integration between the modules of the system.
Fundação de Amparo a Pesquisa do Estado de Alagoas
Um processo de calibração de câmera consiste no problema de determinar as características geométricas digitais e ópticas da câmera a partir de um conjunto de dados iniciais. Este problema pode ser dividido em três etapas: aquisição de dados iniciais, o processo de calibração em si e otimização. Este trabalho propõe o desenvolvimento de uma ferramenta de calibração baseada em uma arquitetura genérica para qualquer processo de calibração. Para este propósito, o sistema apresentado neste trabalho permite a personalização de cada etapa da calibração. A inclusão de novos métodos de calibração é realizada de forma dinâmica, permitindo assim maior integração e flexibilidade entre os módulos do sistema.

Tradicionalment, la reproducció del mon real se'ns ha mostrat a traves d'imatges planes. Aquestes imatges se solien materialitzar mitjançant pintures sobre tela o be amb dibuixos. Avui, per sort, encara podem veure pintures fetes a ma, tot i que la majoria d'imatges s'adquireixen mitjançant càmeres, i es mostren directament a una audiència, com en el cinema, la televisió o exposicions de fotografies, o be son processades per un sistema computeritzat per tal d'obtenir un resultat en particular. Aquests processaments s'apliquen en camps com en el control de qualitat industrial o be en la recerca mes puntera en intel·ligència artificial. Aplicant algorismes de processament de nivell mitja es poden obtenir imatges 3D a partir d'imatges 2D, utilitzant tècniques ben conegudes anomenades Shape From X, on X es el mètode per obtenir la tercera dimensió, i varia en funció de la tècnica que s'utilitza a tal nalitat. Tot i que l'evolució cap a la càmera 3D va començar en els 90, cal que les tècniques per obtenir les formes tridimensionals siguin mes i mes acurades. Les aplicacions dels escàners 3D han augmentat considerablement en els darrers anys, especialment en camps com el lleure, diagnosi/cirurgia assistida, robòtica, etc. Una de les tècniques mes utilitzades per obtenir informació 3D d'una escena, es la triangulació, i mes concretament, la utilització d'escàners laser tridimensionals. Des de la seva aparició formal en publicacions científiques al 1971 [SS71], hi ha hagut contribucions per solucionar problemes inherents com ara la disminució d'oclusions, millora de la precisió, velocitat d'adquisició, descripció de la forma, etc. Tots i cadascun dels mètodes per obtenir punts 3D d'una escena te associat un procés de calibració, i aquest procés juga un paper decisiu en el rendiment d'un dispositiu d'adquisició tridimensional. La nalitat d'aquesta tesi es la d'abordar el problema de l'adquisició de forma 3D, des d'un punt de vista total, reportant un estat de l'art sobre escàners laser basats en triangulació, provant el funcionament i rendiment de diferents sistemes, i fent aportacions per millorar la precisió en la detecció del feix laser, especialment en condicions adverses, i solucionant el problema de la calibració a partir de mètodes geomètrics projectius.
Traditionally, the reproduction of the real world has been shown to us by means of at images. These images used to be materialised by means of paint on canvas, drawings or the like. Today, we still see hand made pictures, by fortune, although most of the images are acquired by cameras and they are either directly shown to an audience, like in the cinema, television or photographs, or they are processed by a computer system in order to obtain a particular result, like in industrial quality assurance or bleeding edge artificial intelligence research. Applying mid-level processing algorithms, 3D images can be obtained from 2D ones, using well known techniques called Shape From X, where X is the method for obtaining the 3rd dimension. While the evolution to the 3D camera begun in the 90s, the techniques for obtaining the most accurate 3D shape need to be continuously improving. The application of 3D scanners has spread signi cantly in the recent years, specially in elds like entertainment, assisted diagnosis/ surgery, robotics, etc. One of the most used techniques to obtain 3D information from a scene is triangulation, and more concretely, triangulationbased laser scanners. Since their formal appearance in scienti c publications, in 1971 [SS71], there have been contributions for solving inherent problems like occlusion avoidance, accuracy improvement, acquisition speed, shape description, etc. All of the methods for obtaining 3D points of a scene is accompained with a calibration procedure, and this procedure plays a decisive role in the performance of the acquisition device. The goal of this thesis is to provide a holistic approach to the problem of shape acquisition, giving a wide survey of triangulation laser scanners, testing the performance of di erent systems, and to give contributions for both improving acquisition accuracy under adverse conditions and solving the calibration problem. In addition, the calibration approach is based on previous works that used projective geometry to this end.

A economia mundial, cada vez mais competitiva, impulsiona o acelerado desenvolvimento tecnológico e conseqüentemente promove o crescente uso de Máquinas de Medir a Três Coordenadas (MM3Cs). A preferência por essas máquinas pode ser justificada pela sua grande flexibiÍidade e produtividade e é uma tentativa de melhorar a área de inspeção dimensional do processo produtivo. Um grande esforço no desenvolvimento de novas metodologias se realiza para se obter e modelar os erros de MM3Cs. Padrões para calibração de MM3Cs foram sugeridos e colocados em uso através dos diferentes anos, com a finalidade de utilizá-los em testes de aceitação e verificação periódica da incerteza de medição de MM3Cs. Novos artefatos para a calibração indireta de MM3Cs visam melhorar os procedimentos de calibração para uso em sistemas de compensação de erros. Diante do exposto acima, este trabalho tem como objetivo desenvolver um Procedimento de Calibração Indireta de MM3Cs com o Esquadro Mecânico de Esferas aliado a um Modelo Reduzido de Sintetização de Erros (MRSE) para uso em um Sistema de Compensação de Erros. O procedimento possibilita maior rapidez na obtenção dos valores e comportamentos dos erros quando comparado com outros procedimentos de calibração indireta. Aliado a um MRSE, o procedimento proposto tem como vantagem o uso de um único artefato para medir todos os termos das componentes do erro volumétrico, nas direções X, Y e Z de uma MM3C.
The increasingly competitive world economy promotes the technological development and, as a consequence, the growing use of Coordinate Measuring Machines (CMMs). The predilection for CMMs can be justified by their great flexibility and productivity and is also an attempt to improve the dimerisional inspection quality of the productive process. Considerable effort was made on the development of new methodologies to obtain and model CMMs errors. Calibration standards were suggested and employed for years aiming at acceptance tests and periodic verification of measurement uncertainty of CMMs. The development of new artefacts for CMM indirect calibration seeks to enhance calibration procedures for error compensation systems. Therefore, this work aims at the development of an indirect CMM calibration procedure using a mechanical ball square and the Error Synthesization Reduced Model (ESRM) for an error compensation system. The procedure allows faster obtaining of error values and behaviour if compared with other indirect calibration procedures. The proposed procedure, along with the ESRM, is advantageous since only one artefact is employed to measure all the terms of the volumetric error components m directions X, Y and Z of the CMM.

The main theme of this master thesis is the design of technological process measurement and processing of measured data entered crane tracks to determine the geometric parameters of these crane tracks. Diploma thesis further describes the procedure for testing and possible rectification surveying equipment and instrumentation. The thesis is divided of 7 parts, contains 31 images, 4 graphs, 44 tables and 13 attachments. The theoretical part of this thesis contains information about several types of cranes, methods of measurement and processing, as well information on legal and technical regulations related to this topic of the thesis. The fourth and fifth parts of this thesis provides information on selected crane tracks on which the measurements were taken, the choice of methods of measurement, processing technique and the results obtained. The final part of the thesis includes evaluation of the results obtained, comparing methods of measurement, processing, evaluation and design of a technique of determining the geometric parameters of crane tracks.

Gegenstand der vorliegenden Dissertation ist die Entwicklung von Kalibrierverfahren und Algorithmen zur Bildverarbeitung im Kontext von Multiprojektorsystemen mit dem Ziel, die Einsatzmöglichkeiten von derartigen Anlagen zu erweitern und die Nutzerakzeptanz solcher Systeme zu steigern. Die Arbeit konzentriert sich dabei insbesondere auf (annähernd) planare Mehrsegment-Projektionsanlagen, die aus preisgünstigen, nicht speziell für den Visualisierungbereich konzipierten Consumer- und Office-Projektoren aufgebaut werden. Im ersten Teil der Arbeit werden bestehende Verfahren zur geometrischen Kalibrierung, zum Edge-Blending sowie zur Helligkeits- und Farbanpassung auf ihre Eignung im Hinblick auf die Anforderungen untersucht und Erweiterungen entwickelt. Für die kamerabasierte Geometrie- Kalibrierung wird mit Lininenpattern gearbeitet, wobei ein effizienter rekursiver Algorithmus zur Berechnung der Schnittpunkte bei leicht gekrümmten Oberflächen vorgestellt wird. Für das Edge-Blending wird ein generalisiertes Modell entwickelt, das mehrere bestehende Ansätze kombiniert und erweitert. Die vorgenommene Modifikation der Distanzfunktion erlaubt insbesondere die bessere Steuerung des Helligkeitsverlaufs und ermöglicht weichere Übergänge an den Grenzen der Überlappungszonen. Es wird weiterhin gezeigt, dass das Edge-Blending mit bestehenden Ansätzen zum Ausgleich der Helligkeitsunterschiede wie Luminance Attenutation Maps kombiniert werden kann. Für die photometrische Kalibrierung ist die Kenntnis der Farb-Transferfunktion, also der Abbildung der Eingabe-Farbwerte auf die tatsächlich vom Projektor erzeugten Ausgaben, unerlässlich. Die herkömmlichen Ansätze betrachten dabei vorwiegend RGB-Projektoren, bei denen die dreidimensionale Transferfunktion in drei eindimensionale Funktionen für jeden Farbkanal zerlegt werden kann. Diese Annahme trifft jedoch auf die betrachteten Projektoren meist nicht zu. Insbesondere DLP-Projektoren mit Farbrad verfügen oft über zusätzliche Grundfarben, so dass der Farbraum deutlich von einem idealen RGB-Modell abweicht. In dieser Arbeit wird zunächst ein empirisches Modell einer Transferfunktion vorgestellt, das sich für derartige Projektoren besser eignet, allerdings die Helligkeit der Projektoren nicht vollständig ausnutzt. Im zweiten Teil der Arbeit wird ein kamerabasiertes Messverfahren entwickelt, mit dem direkt die dreidimensionale Farb-Transferfunktion ermittelt werden kann. Gegenüber bestehenden Verfahren werden tausende von Farbsamples gleichzeitig erfasst, so dass die erreichbare Sampledichte unter praxisrelevanten Messbedingungen von 17x17x17 auf 64x64x64 erhöht und damit die Qualität der photometrischen Kalibrierung signifikant gesteigert werden kann. Weiterhin wird ein Schnellverfahren entwickelt, dass die Messungsdauer bei 17x17x17 Samples von mehreren Stunden mit bisherigen Verfahren auf weniger als 30 Minuten reduziert. Im dritten Teil werden Algorithmen zur effizienten Bildverarbeitung entwickelt, die der GPU-basierten Anwendung der Kalibrierparameter auf die darzustellenden Bilddaten in Echtzeit dienen. Dabei werden die Möglichkeiten zur Vermeidung redundanter Berechnungsschritte beim Einsatz Stereoskopie-fähiger Projektoren ausgenutzt. Weiterhin wird das eigentliche Kalibrierverfahren effizient mit Verfahren zur Konvertierung von stereoskopischen Bildverfahren kombiniert. Es wird gezeigt, dass ein einzelner PC aus Standardkomponenten zur Ansteuerung einer Mehrsegment-Projektionsanlage mit bis zu 6 Projektoren ausreicht. Die Verwendung von DVI-Capture-Karten ermöglicht dabei den Betrieb einer solchen Anlage wie einen "großen Monitor" für beliebige Applikationen und Betriebssysteme.

Aquesta tesi s'emmarca dins del projecte CICYT TAP 1999-0443-C05-01. L'objectiu d'aquest projecte és el disseny, implementació i avaluació de robots mòbils, amb un sistema de control distribuït, sistemes de sensorització i xarxa de comunicacions per realitzar tasques de vigilància. Els robots han de poder-se moure per un entorn reconeixent la posició i orientació dels diferents objectes que l'envolten. Aquesta informació ha de permetre al robot localitzar-se dins de l'entorn on es troba per poder-se moure evitant els possibles obstacles i dur a terme la tasca encomanada. El robot ha de generar un mapa dinàmic de l'entorn que serà utilitzat per localitzar la seva posició. L'objectiu principal d'aquest projecte és aconseguir que un robot explori i construeixi un mapa de l'entorn sense la necessitat de modificar el propi entorn.
Aquesta tesi està enfocada en l'estudi de la geometria dels sistemes de visió estereoscòpics formats per dues càmeres amb l'objectiu d'obtenir informació geomètrica 3D de l'entorn d'un vehicle. Aquest objectiu tracta de l'estudi del modelatge i la calibració de càmeres i en la comprensió de la geometria epipolar. Aquesta geometria està continguda en el que s'anomena emph{matriu fonamental}. Cal realitzar un estudi del càlcul de la matriu fonamental d'un sistema estereoscòpic amb la finalitat de reduir el problema de la correspondència entre dos plans imatge. Un altre objectiu és estudiar els mètodes d'estimació del moviment basats en la geometria epipolar diferencial per tal de percebre el moviment del robot i obtenir-ne la posició. Els estudis de la geometria que envolta els sistemes de visió estereoscòpics ens permeten presentar un sistema de visió per computador muntat en un robot mòbil que navega en un entorn desconegut. El sistema fa que el robot sigui capaç de generar un mapa dinàmic de l'entorn a mesura que es desplaça i determinar quin ha estat el moviment del robot per tal de emph{localitzar-se} dins del mapa.
La tesi presenta un estudi comparatiu dels mètodes de calibració de càmeres més utilitzats en les últimes dècades. Aquestes tècniques cobreixen un gran ventall dels mètodes de calibració clàssics. Aquest mètodes permeten estimar els paràmetres de la càmera a partir d'un conjunt de punts 3D i de les seves corresponents projeccions 2D en una imatge. Per tant, aquest estudi descriu un total de cinc tècniques de calibració diferents que inclouen la calibració implicita respecte l'explicita i calibració lineal respecte no lineal. Cal remarcar que s'ha fet un gran esforç en utilitzar la mateixa nomenclatura i s'ha estandaritzat la notació en totes les tècniques presentades. Aquesta és una de les dificultats principals a l'hora de poder comparar les tècniques de calibració ja què cada autor defineix diferents sistemes de coordenades i diferents conjunts de paràmetres. El lector és introduït a la calibració de càmeres amb la tècnica lineal i implícita proposada per Hall i amb la tècnica lineal i explicita proposada per Faugeras-Toscani. A continuació es passa a descriure el mètode a de Faugeras incloent el modelatge de la distorsió de les lents de forma radial. Seguidament es descriu el conegut mètode proposat per Tsai, i finalment es realitza una descripció detallada del mètode de calibració proposat per Weng. Tots els mètodes són comparats tant des del punt de vista de model de càmera utilitzat com de la precisió de la calibració. S'han implementat tots aquests mètodes i s'ha analitzat la precisió presentant resultats obtinguts tant utilitzant dades sintètiques com càmeres reals.
Calibrant cada una de les càmeres del sistema estereoscòpic es poden establir un conjunt de restriccions geomètri ques entre les dues imatges. Aquestes relacions són el que s'anomena geometria epipolar i estan contingudes en la matriu fonamental. Coneixent la geometria epipolar es pot: simplificar el problema de la correspondència reduint l'espai de cerca a llarg d'una línia epipolar; estimar el moviment d'una càmera quan aquesta està muntada sobre un robot mòbil per realitzar tasques de seguiment o de navegació; reconstruir una escena per aplicacions d'inspecció, propotipatge o generació de motlles. La matriu fonamental s'estima a partir d'un conjunt de punts en una imatges i les seves correspondències en una segona imatge. La tesi presenta un estat de l'art de les tècniques d'estimació de la matriu fonamental. Comença pels mètode lineals com el dels set punts o el mètode dels vuit punts, passa pels mètodes iteratius com el mètode basat en el gradient o el CFNS, fins arribar las mètodes robustos com el M-Estimators, el LMedS o el RANSAC. En aquest treball es descriuen fins a 15 mètodes amb 19 implementacions diferents. Aquestes tècniques són comparades tant des del punt de vista algorísmic com des del punt de vista de la precisió que obtenen. Es presenten el resultats obtinguts tant amb imatges reals com amb imatges sintètiques amb diferents nivells de soroll i amb diferent quantitat de falses correspondències.
Tradicionalment, l'estimació del moviment d'una càmera està basada en l'aplicació de la geometria epipolar entre cada dues imatges consecutives. No obstant el cas tradicional de la geometria epipolar té algunes limitacions en el cas d'una càmera situada en un robot mòbil. Les diferencies entre dues imatges consecutives són molt petites cosa que provoca inexactituds en el càlcul de matriu fonamental. A més cal resoldre el problema de la correspondència, aquest procés és molt costós en quant a temps de computació i no és gaire efectiu per aplicacions de temps real. En aquestes circumstàncies les tècniques d'estimació del moviment d'una càmera solen basar-se en el flux òptic i en la geometria epipolar diferencial. En la tesi es realitza un recull de totes aquestes tècniques degudament classificades. Aquests mètodes són descrits unificant la notació emprada i es remarquen les
semblances i les diferencies entre el cas discret i el cas diferencial de la geometria epipolar. Per tal de poder aplicar aquests mètodes a l'estimació de moviment d'un robot mòbil, aquest mètodes generals que estimen el moviment d'una càmera amb sis graus de llibertat, han estat adaptats al cas d'un robot mòbil que es desplaça en una superfície plana. Es presenten els resultats obtinguts tant amb el mètodes generals de sis graus de llibertat com amb els adaptats a un robot mòbil utilitzant dades sintètiques i seqüències d'imatges reals.
Aquest tesi finalitza amb una proposta de sistema de localització i de construcció d'un mapa fent servir un sistema estereoscòpic situat en un robot mòbil. Diverses aplicacions de robòtica mòbil requereixen d'un sistema de localització amb l'objectiu de facilitar la navegació del vehicle i l'execució del les trajectòries planificades. La localització es sempre relativa al mapa de l'entorn on el robot s'està movent. La construcció de mapes en un entorn desconegut és una tasca important a realitzar per les futures generacions de robots mòbils. El sistema que es presenta realitza la localització i construeix el mapa de l'entorn de forma simultània. A la tesi es descriu el robot mòbil GRILL, que ha estat la plataforma de treball emprada per aquesta aplicació, amb el sistema de visió estereoscòpic que s'ha dissenyat i s'ha muntat en el robot. També es descriu tots el processos que intervenen en el sistema de localització i construcció del mapa. La implementació d'aquest processos ha estat possible gràcies als estudis realitzats i presentats prèviament (calibració de càmeres, estimació de la matriu fonamental, i estimació del moviment) sense els quals no s'hauria pogut plantejar aquest sistema. Finalment es presenten els mapes en diverses trajectòries realitzades pel robot GRILL en el laboratori.
Les principals contribucions d'aquest treball són:
·Un estat de l'art sobre mètodes de calibració de càmeres. El mètodes són comparats tan des del punt de vista del model de càmera utilitzat com de la precisió dels mètodes.
·Un estudi dels mètodes d'estimació de la matriu fonamental. Totes les tècniques estudiades són classificades i descrites des d'un punt de vista algorísmic.
·Un recull de les tècniques d'estimació del moviment d'una càmera centrat en el mètodes basat en la geometria epipolar diferencial. Aquestes tècniques han estat adaptades per tal d'estimar el moviment d'un robot mòbil.
·Una aplicació de robòtica mòbil per tal de construir un mapa dinàmic de l'entorn i localitzar-se per mitja d'un sistema estereoscòpic. L'aplicació presentada es descriu tant des del punt de vista del maquinari com del programari que s'ha dissenyat i implementat.
Human eyes have been widely studied by the scientific community so that its operation principle is widely known. Computer vision tries to copy the way human beings perceive visual information by means of using cameras acting as eyeballs and computers aspiring to process this information in an --intelligent way". The complex task of being conscious of reality is obviously divided into a set of simpler problems which covers from image acquisition to scene description. One of the main applications is robot perception in which a mobile robot is equipped with a computer vision system. Robots may be able to navigate around an unknown structured environment acquiring visual information of their surroundings with the aim of estimating the position and orientation of every obstacle. Moreover, the pose of the vehicle has to be estimated as accurate as possible. Hence, the motion of the vehicle might be also computed allowing the localization of the vehicle with respect to the 3D map.
This thesis is focused on the study of the geometry involved in stereo vision systems composed by two cameras with the aim of obtaining 3D geometric information of the vehicle surroundings. This objective deals to the study of camera modelling and calibration and the comprehension of the epipolar geometry. Then, the computation of the fundamental matrix of a stereoscopic system is surveyed with the aim of reducing the correspondence problem between both image planes. An accurate estimation of the fundamental matrix allows us not only to compute 3D information of the vehicle environments, but to validate it. Nevertheless, the traditional case of the epipolar geometry has some limitations in the common case of a single camera attached to a mobile robot. Disparities between two consecutive images are rather small at common image rates leading to numerical inaccuracies on the computation of the fundamental matrix. Then, another objective is the study of general vision-based egomotion estimation methods based on the differential epipolar constraint with the aim of perceiving the robot movement instead of its position.
The study of the geometry involved in stereo vision systems leads us to present a computer vision system mounted on a vehicle which navigates in an unknown environment. Two main tasks are faced: a) the localization of the vehicle; and b) the building of an absolute 3D map.
El sistema de visión humano ha sido ampliamente estudiado por la comunidad científica de forma que su principio de funcionamiento es profundamente conocido. La Visión por Computador trata de copiar la forma que nosotros los humanos percibimos la información visual por medio del uso de cámaras actuando como ojos y un ordenador aspirando a procesar toda la información de "forma inteligente". La compleja tarea de ser consciente de la realidad es obviamente dividida en un conjunto de problemas mucho más simples, los cuales abarcan des de la adquisición de la imagen a la descripción de la escena. Una de las numerosas aplicaciones es la percepción por parte de un robot, donde un robot móvil es equipado con un sistema informático de visión por computador. Estos robots deben ser capaces de navegar a lo largo de un entorno estructurado desconocido mediante la adquisición de información visual de su alrededor, con el objetivo de estimar la posición y orientación de todos los obstáculos. Además, la posición del vehículo debe ser estimada de la forma más precisa posible. De esta forma, el movimiento del vehículo puede ser también calculado lo que permite la localización del vehículo con respeto al mapa 3D.
Esta tesis profundiza en el estudio de la geometría existente en los sistemas de visión estéreo compuestos por dos cámaras con la intención de obtener información geométrica 3D del entorno del vehículo. Este objetivo lleva consigo la necesidad inicial de realizar un estudio de modelado de la cámara y calibración, y la compensación de la geometría epipolar. A continuación, el cálculo de la matriz fundamental de un sistema esteresocópico es analizado para reducir el problema de la correspondencia entre ambos planos de la imagen. Una estimación precisa de la matriz fundamental nos permite no solamente obtener la información 3D del entorno, sino también validar la misma. No obstante, la geometría epipolar tradicional sufre algunas limitaciones en el caso de una cámara montada en un robot móvil. La disparidad entre dos imágenes consecutivas es realmente mínima trabajando a velocidad estándar lo que conlleva a errores numéricos en el cálculo de la matriz fundamental. Por esta razón, otro objetivo es el estudio de los métodos de estimación del movimiento basados en la geometría epipolar diferencial con el objetivo de pervivir el movimiento del robot y su posición.
El estudio de la geometría inmersa en los sistemas de visión estéreo nos lleva a presentar un sistema de visión por computador montado en un vehículo capaz de navegar en un entorno desconocido. Dos tareas básicas son consideradas: a) la localización del vehículo; y b) la construcción de un mapa 3D absoluto.

碩士
中華大學
電機工程學系碩士在職專班
101
An ideal lens system can show the image the same as the scene no matter the object in the scene is located at the center or the edge of the image. However, practical lenses system has distortion more or less, but we can sense it or not. Generally, the lens system with large field of view has obvious distortion, e.g., fish-eye lens and wide-angle lens. In this experiment, we measure and analyze the geometric distortion of a fish-eye lens system. The lens system is calibrated and a distorted test image is corrected. Most of the distortion of a fish-eye lens is radial distortion, i.e., the distortion is related with the distance from the image center. We assume a polynomial function in terms of the distance from the image center to describe the distortion. The result shows that fourth order polynomial is good enough to correct the image.

碩士
中華大學
電機工程學系碩士班
102
When the picture of an object is not perpendicularly taken by a camera, the captured image is distorted due to the view angle and the magnifying power that depends on object distance. For an example, if a circle is shot with a small tilt angle, its captured image resembles an ellipse due to view angle. If it is shot with a large tilt angle, its captured image apparently does not resemble an ellipse due to magnifying power in addition to view angle. This thesis measured and analyzed the geometric distortions of images due to the tilt angle. The images are calibrated and recovered. A restoration function based on the distance from the center point of the image is defined. We showed that images can be recovered with this restoration distortion. But for the case with a large tilt angle, the recovered image is blurred due to the limited depth of field. For the experimental condition of this thesis, the recovered image is poor for the tilt angle larger than about 60 degrees.

This paper describes a simple method for internal camera calibration for computer vision. This method is based on tracking image features through a sequence of images while the camera undergoes pure rotation. The location of the features relative to the camera or to each other need not be known and therefore this method can be used both for laboratory calibration and for self calibration in autonomous robots working in unstructured environments. A second method of calibration is also presented. This method uses simple geometric objects such as spheres and straight lines to The camera parameters. Calibration is performed using both methods and the results compared.

碩士
國立臺灣大學
資訊工程學研究所
94
In the thesis I focus on solving the geometric and photometric problems, especially the photometric problem, when building a seamless large display by tiling multiple projectors. Previous work related to photometric calibration mainly addresses either color gamut matching, or luminance balancing while the chrominance variation problem was ignored. Here, a two-phase approach for photometric calibration is proposed to achieve not only chrominance consistency but also perceptual luminance uniformity across the multi-projector display. In the first phase, we present an approach similar to Stone''s work on color gamut matching. Different to Stone''s work is that we derive the color gamut of the display based on preserving the maximum luminance for each projector. Afterward, the second phase eliminates the variance in luminance by using a perceptual method proposed by Majumder and Stevens. However, our method is more efficient because it only needs to generate one luminance attenuation map, rather than deals with each channel separately. The experimental results show that our work successfully deals with both color matching and luminance balancing with high display quality. Even though the tiled display is composed of projectors of different models, our method can also achieve a seamless result. Our method has great potential for many applications that require large and high-resolution displays, such as scientific visualizations and visual display walls.

Wu, Dan.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2008.
Includes bibliographical references (leaves 62-63).
Abstracts in English and Chinese.
Chapter 1 --- Introduction --- p.6
Chapter 2 --- Calibrated Geometry --- p.9
Chapter 2.1 --- Theory of calibrations --- p.9
Chapter 2.2 --- Two classical examples --- p.14
Chapter 2.3 --- Calibrations and the VCP-forms --- p.19
Chapter 3 --- Constructing Calibrations --- p.23
Chapter 3.1 --- Clifford algebra and Spin groups --- p.23
Chapter 3.2 --- Calibrations and spinors --- p.30
Chapter 4 --- Calibrations in Exceptional Geometry --- p.39
Chapter 4.1 --- G2 calibration --- p.40
Chapter 4.2 --- Cayley calibration --- p.49
Bibliography --- p.62

Road safety is an evolving area of research that underpins the continuous attempt to build safe and cost-efficient roads. Despite the considerable growth of the road safety literature, some concern remains regarding the safety level associated with standard geometric design models. The central concern is that the level of safety delivered by design standards is implicit and largely unknown. Accordingly, it remains difficult to form a judgment regarding the acceptability and the consistency of the safety level built in design standards. In order to account for the previous concern, road safety is quantified in the present practice by explicitly developed analytical tools or safety evaluation models. Those analytical tools, to some extent, guide the designer in investigating the safety consequences of different dimensioning scenarios for a highway design. However, in order to elicit and examine the implicit safety level in design standards, a quantifiable measure must be used to assess road safety. A parallel system is formulated for the assessment of safety levels in standard design outputs by tracing the propagation of uncertainty. Uncertainty can be incorporated into the design process through a probabilistic framework. Reliability theory, a subset of probability theory, offers a rational foundation for calculating the propagation of uncertainty throughout the design process. The main proposition that underlies the analysis presented in this thesis is that design safety level associated with standard design outputs should be consistent and close to a premeditated level. Several discussions are presented that suggest different methods of selecting a target design safety level. A general framework for calibrating standard design models is presented in accordance with the previous preposition. The thesis contains an application of the calibration framework to the standard design model of crest vertical curves. In order to study the effect of model uncertainty, represented by the combination of horizontal and vertical curves, a new sight distance model is formulated that enables the calculation of available sight distance in three-dimensional environment. The sight distance model is further augmented to the process of reliability analysis. The calibrated design charts are constructed in order to yield consistent design safety level.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

Tese de doutoramento em Engenharia Electrotécnica e de Computadores, no ramo de Especialização em Automação e Robótica, apresentada ao Departamento de Engenharia Electrotécnica e de Computadores da Universidade de Coimbra
This thesis addresses minimal problems that involve multiple cameras or a combination of cameras with other sensors, particularly focusing on four cases: extrinsic calibration between a camera and a laser rangefinder (LRF); full calibration of an ultrasound array (US) with a camera; full calibration of a camera within a calibrated network; relative pose between axial systems. The first problem (LRF-Camera) is highly important in the context of mobile robotics in order to fuse the information of an LRF and a Camera in localization maps. The second problem (US-Camera) is becoming increasingly relevant in the context of medical imaging to perform guided intervention and 3D reconstruction with US probes. Both these problems use a planar calibration target to obtain a minimal solution from 3 and 4 correspondences respectively. They are formulated as the registration between planes detected by the camera and lines detected by either the LRF or the US. The third problem (Camera-Network) is concerned with two application scenarios: addition of a new camera to a calibrated network, and tracking of a hand-held camera within the field of view of a calibrated network. The last problem (Axial System) has its main application in motion estimation of stereo camera pairs. Both these problems introduce a 5-dimensional linear subspace to model line incidence relations of an axial system, of which a pair of calibrated cameras is a particular example. In the Camera-Network problem a generalized fundamental matrix is derived to obtain a 11-correspondence minimal solution. In the Axial System problem a generalized essential matrix is derived to obtain a 10-correspondence non-minimal solution. Although it should be possible to solve this last problem with as few as 6 correspondences, the proposed solution is the closest to minimal in the literature. Additionally this thesis addresses the use of the RANSAC framework in the context of the problems mentioned above. While RANSAC is the most widely used method in computer vision for robust estimation when minimal solutions are available, it cannot be applied directly to some of the problems discussed here. A new framework -- multi-RANSAC -- is presented as an adaptation of RANSAC to problems with multiple sampling datasets. Problems with multiple cameras or multiple sensors often fall in this category and thus this new framework can greatly improve their results. Its applicability is demonstrated in both the US-Camera and the Camera-Network problems.
Esta tese aborda os problemas mínimos no contexto de visão por computador, isto é, problemas com o mesmo número de restrições e de parâmetros desconhecidos, para os quais existe um conjunto finito e discreto de soluções. A tese foca-se em particular nos seguintes problemas: calibração extrínseca entre uma câmara e um sensor laser rangefinder (LRF); calibração completa de uma sonda ultrasom (US) com uma câmara; calibração completa de uma câmara dentro de uma rede calibrada; estimação de pose relativa entre sistema axiais. O primeiro problema (LRF-Camera) é extremamente importante no contexto de robótica móvel para fundir a informação de um sensor LRF e uma câmara em mapas de localização. O segundo problema (US-Camera) está-se a tornar cada vez mais relevante no contexto de imagiologia médica para realizar intervenções guiadas e reconstrução 3D com sondas ecográficas. Ambos os problemas usam um alvo de calibração planar para obter uma solução mínima usando 3 e 4 correspondências respectivamente, e são formulados como o registo 3D entre planos detectados pela câmara e linhas detectadas pelo LRF ou US. O terceiro problema (Camera-Network) tem duas aplicações em mente: a introdução de uma nova câmara numa rede calibrada, e o seguimento de uma câmara guiada manualmente dentro do campo de visão de uma rede calibrada. O último problema (Axial System) tem a sua maior aplicação na estimação de pose relativa entre pares de câmaras estéreo. Em ambos os problemas é introduzido um subespaço linear em 5 dimensões que modela as relações de incidência de linhas num sistema axial, do qual as câmaras estéreo são um caso particular. No problema Camera- Network é introduzida uma generalização da matriz fundamental que permite obter uma solução mínima com 11 correspondências. No problema Axial System é introduzida uma generalização da matrix essencial que permite obter uma solução não mínima com 10 correspondências. Apesar de ser possível, em teoria, resolver este último problema com apenas 6 correspondências, a solução apresentada nesta tese usa um menor número de correspondências que as alternativas existentes. Adicionalmente esta tese aborda o uso de RANSAC no contexto dos problemas anteriormente descritos. O RANSAC é o estimador robusto mais utilizado em visão por computador quando existem soluções mínimas para um determinado problema, no entanto não pode ser aplicado directamente em algumas das aplicações aqui descritas. Um novo método é proposto – multiset-RANSAC – que adapta o RANSAC para situações que envolvem a amostragem de múltiplos conjuntos de dados. Os problemas com múltiplas câmaras ou múltiplos sensores encontram-se mutas vezes nesta categoria, tornando o multiset-RANSAC numa ferramenta que pode melhorar bastante os resultados em alguns dos problemas focados nesta tese. A utilidade deste método é demonstrada nos problemas US-Camera e Camera-Network.

博士
國立成功大學
工程科學系
107
With the advancement of precision manufacturing, the precision requirements of the manufacturing equipment are constantly increasing. The finished products are moved toward two trends: one is that the product size is downsized into micro-/nano-meter scale, the other one is the product size is enlarged. Regardless of which situation, the inspection technology of the manufacturing equipment is regarded as an important issue. Most errors in a manufacturing equipment system come from the assembly process and component quality. The aims of this study is to develop a high accuracy, high efficiency, and low cost inspection system which is used to inspect or measure various degrees of freedom (DOF) errors and assembly errors. In terms of multi-DOF error inspection, the main purpose of this research is to develop a measurement system which can measure the multi-degree of freedom error caused by the manufacturing equipment during assembly and movement processes. Three kinds of high-precision detection systems are constructed, including a geometric error measurement system for linear guideway assembly and calibration, the machine tool bi-axial straightness error detection system, and the machine tool rotary axis angle error detection system. The proposed system can be applied for detecting and analysis of motion errors such as machine tools, three-dimensional measuring beds, high-precision X-Y platforms, and linear slides. The developed detection system mainly integrates optical design, electronic signal processing and mathematical simulation analysis. It can be applied to the detection of related equipment such as precision machinery, optoelectronic industry and semiconductor industry.

碩士
中華大學
機械與航太工程研究所
93
Recently, 3D computer vision has been widely used in the application areas like robot vision, industrial metrology, and measurement of deformations in material. Hence camera calibration techniques were developed to acquire the relationship between the 3D object coordinates and the image coordinates. In the paper a new method of camera calibration is proposed to calibrate a stereo vision to measure the deformation field of a material with micron measurement accuracy. The center positions of circle dots were used as calibration points. Since the projection of the circle dot on the image plane is an ellipse, the relationship between the center of the circle dot and the center of the ellipse was obtained mathematically in the paper to reduce the bias between the camera model and the observed center of the ellipses. In addition, both of the radial and decentering lens distortions are included in the camera model equation to improve the accuracy of the model equation. After camera calibration, the tensile tests on the double dots specimen, the dot grids specimen, and the random pattern specimen were conducted and the calibrated stereo vision was used to measure the deformation field of the specimens and calculate the axial strain, lateral strain, and Poisson’s ratio to evaluate the ability of the stereo vision to measure a deformed body.

碩士
國立中正大學
機械工程學系
85
There are two categories to improve the machining accuracy for industry machine tools. One is using high accuracy machine tools, the other is error calibration and error compensation. The purpose of this research is to find out the geometric errors with a fast error calibration system, which can automatically track the laser path.Works of this research include: 1) the derivation of volumetric error model, 2) the computer simulation of straightness error calculation, 3) experimental results of volumetric error model.

碩士
國立成功大學
測量及空間資訊學系碩博士班
95
Ground-based LiDAR(Light Detection and Ranging) has became a novel instrument to applications of engineering because of its advantages of high accuracy and efficiency for 3D measuring. Related applications include civil engineering, building reconstruction, deformation monitoring, architecture maintaining, and so on. The collected data, called point clouds, may introduce systematic errors if the LiDARs are not well calibrated, which would influence the positioning accuracy. Although sending the instrument back to the factory for calibration is a way to solve the questions, it is inefficient and uneconomic. In this paper, we propose a standard procedure of ground-based LiDAR calibration. By the designed calibration field, the mathematic model of systematic error would be established and applied to eliminate possible systematic errors. The indoor and outdoor calibration fields are established by attaching reflecting targets on walls and pillars of buildings. The 3D coordinates of targets are derived from both total station and ground-based LiDAR measurements, and transform into union coordinate system through 3D coordinate transformation. The adjustment of six-parameters and seven-parameters transformation with additional error parameters would be employed to model possible systematic errors to find out error sources. To analysis RMSEs of adjustment, the experiment result shows that the accuracy can acquire improvement after calibration. It proves that the proposed method is feasible and gets the expected result.