A review of point set registration: from pairwise registration to groupwise registration

Abstract: This paper presents a comprehensive literature review on point set registration. The state-of-the-art modeling methods and algorithms for point set registration are discussed and summarized. Special attention is paid to methods for pairwise registration and groupwise registration. Some of the most prominent representative methods are selected to conduct qualitative and quantitative experiments. From the experiments we have conducted on 2D and 3D data, CPD-GL pairwise registration algorithm [1] and JRMPC groupwise registration algorithm [2,3] seem to outperform their rivals both in accuracy and computational complexity. Furthermore, future research directions and avenues in the area are identified

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

A critical analysis of local and global cultural factors in graphic wayfinding design: a case study of Beijing

The main intentions of this thesis are to analyse and explain changes in the function and graphic components of Beijing s wayfinding systems and to explain how the systems construct multiple cultural and political identities at different historical periods and in changing local/global contexts. In the thesis, the oversimplified one-way theory of the global-local dichotomy, in which the global power of the West is overwhelming and constantly dominant, and the local system of non-Western countries is passive and fragile, is challenged. Instead, this thesis seeks to examine the interactivity and correlation of the local and the global from two perspectives: mobility and reversibility. Looking at mobility is to consider the local and global and their nexus as different interconnections and networks that are constantly and unevenly changing. Reversibility, with which this thesis is most concerned, deals primarily with the reversible relationship of the local and global, namely, that either the local or the global can be dominant. This point is well illustrated by the evolution of Beijing s graphic wayfinding systems function and appearance. Beijing, as the capital of China, has undergone a radical transformation from the fall of the last Empire Qing (1912) to the establishment of the People s Republic of China (1949). The meaning of Beijing varies in accordance with the changes in its political and social structures. There have been five phases in Beijing s development: a well-planned imperial city; a capital city with a republican spirit; a totally industrialised but relatively isolated capital of a socialist country; an open and modernised Chinese-style socialist city; and a cosmopolitan city. In the course of this metamorphosis, what took place was a series of collisions, exchanges, fusions, and re-collisions between local power and global power. Along with the immense changes in Beijing, the role and appearance of the graphic wayfinding systems have also changed, especially those of road signs and doorplates, whose roles have been transformed from that of initial household register to orientation reference, to effective propaganda tool, and then on to the regeneration of a city. Finally, Beijing s graphic wayfinding design within its urban development has been reconfirmed as a useful instrument to support the new forms of visual narratives and consolidate the city brand of Beijing in the 21st century. This study probes into the political and cultural significances behind the changes of the graphic wayfinding systems of Beijing, as well as the interaction between the local and the global as reflected in the formation of these findings. The mutable and reversible relationship between the local and the global is illustrated and clarified through analysis and comparison of various functions and visual elements between Beijing s present graphic wayfinding systems and its early wayfinding signs, as well as decoding the different mainstream political or cultural ideologies that have deeply affected the function and design of Beijing graphic wayfinding systems at different periods

Real Time Sequential Non Rigid Structure from motion using a single camera

En la actualidad las aplicaciones que basan su funcionamiento en una correcta localización y reconstrucción dentro de un entorno real en 3D han experimentado un gran interés en los últimos años, tanto por la comunidad investigadora como por la industrial. Estas aplicaciones varían desde la realidad aumentada, la robótica, la simulación, los videojuegos, etc. Dependiendo de la aplicación y del nivel de detalle de la reconstrucción, se emplean diversos dispositivos, algunos específicos, más complejos y caros como las cámaras estéreo, cámara y profundidad (RGBD) con Luz estructurada y Time of Flight (ToF), así como láser y otros más avanzados. Para aplicaciones sencillas es suficiente con dispositivos de uso común, como los smartphones, en los que aplicando técnicas de visión artificial, se pueden obtener modelos 3D del entorno para, en el caso de la realidad aumentada, mostrar información aumentada en la ubicación seleccionada.En robótica, la localización y generación simultáneas de un mapa del entorno en 3D es una tarea fundamental para conseguir la navegación autónoma. Este problema se conoce en el estado del arte como Simultaneous Localization And Mapping (SLAM) o Structure from Motion (SfM). Para la aplicación de estas técnicas, el objeto no ha de cambiar su forma a lo largo del tiempo. La reconstrucción es unívoca salvo factor de escala en captura monocular sin referencia. Si la condición de rigidez no se cumple, es porque la forma del objeto cambia a lo largo del tiempo. El problema sería equivalente a realizar una reconstrucción por fotograma, lo cual no se puede hacer de manera directa, puesto que diferentes formas, combinadas con diferentes poses de cámara pueden dar proyecciones similares. Es por esto que el campo de la reconstrucción de objetos deformables es todavía un área en desarrollo. Los métodos de SfM se han adaptado aplicando modelos físicos, restricciones temporales, espaciales, geométricas o de otros tipos para reducir la ambigüedad en las soluciones, naciendo así las técnicas conocidas como Non-Rigid SfM (NRSfM).En esta tesis se propone partir de una técnica de reconstrucción rígida bien conocida en el estado del arte como es PTAM (Parallel Tracking and Mapping) y adaptarla para incluir técnicas de NRSfM, basadas en modelo de bases lineales para estimar las deformaciones del objeto modelado dinámicamente y aplicar restricciones temporales y espaciales para mejorar las reconstrucciones, además de ir adaptándose a cambios de deformación que se presenten en la secuencia. Para ello, hay que realizar cambios de manera que cada uno de sus hilos de ejecución procesen datos no rígidos.El hilo encargado del seguimiento ya realizaba seguimiento basado en un mapa de puntos 3D, proporcionado a priori. La modificación más importante aquí es la integración de un modelo de deformación lineal para que se realice el cálculo de la deformación del objeto en tiempo real, asumiendo fijas las formas básicas de deformación. El cálculo de la pose de la cámara está basado en el sistema de estimación rígido, por lo que la estimación de pose y coeficientes de deformación se hace de manera alternada usando el algoritmo E-M (Expectation-Maximization). También, se imponen restricciones temporales y de forma para restringir las ambigüedades inherentes en las soluciones y mejorar la calidad de la estimación 3D.Respecto al hilo que gestiona el mapa, se actualiza en función del tiempo para que sea capaz de mejorar las bases de deformación cuando éstas no son capaces de explicar las formas que se ven en las imágenes actuales. Para ello, se sustituye la optimización de modelo rígido incluida en este hilo por un método de procesamiento exhaustivo NRSfM, para mejorar las bases acorde a las imágenes con gran error de reconstrucción desde el hilo de seguimiento. Con esto, el modelo se consigue adaptar a nuevas deformaciones, permitiendo al sistema evolucionar y ser estable a largo plazo.A diferencia de una gran parte de los métodos de la literatura, el sistema propuesto aborda el problema de la proyección perspectiva de forma nativa, minimizando los problemas de ambigüedad y de distancia al objeto existente en la proyección ortográfica. El sistema propuesto maneja centenares de puntos y está preparado para cumplir con restricciones de tiempo real para su aplicación en sistemas con recursos hardware limitados

Statistical shape modelling: automatic shape model building

Statistical Shape Models (SSM) have wide applications in image segmentation, surface registration and morphometry. This thesis deals with an important issue in SSM, which is establishing correspondence between a set of shape surfaces on either 2D or 3D. Current methods involve either manual annotation of the data (current ‘gold standard’); or establishing correspondences by using segmentation or registration algorithms; or using an information technique, Minimum Description Length (MDL), as an objective function that measures the utility of a model (the state-of-the-art). This thesis presents in principle another framework for establishing correspondences completely automatically by treating it as a learning process. Shannon theory is used extensively to develop an objective function, which measures the performance of a model along each eigenvector direction, and a proper weighting is automatically calculated for each energy component. Correspondence finding can then be treated as optimizing the objective function. An efficient optimization method is also incorporated by deriving the gradient of the cost function. Experimental results on various data are presented on both 2D and 3D. In the end, a quantitative evaluation between the proposed algorithm and MDL shows that the proposed model has better Generalization Ability, Specificity and similar Compactness. It also shows a good potential ability to solve the so-called “Pile Up” problem that exists in MDL. In terms of application, I used the proposed algorithm to help build a facial contour classifier. First, correspondence points across facial contours are found automatically and classifiers are trained by using the correspondence points found by the MDL, proposed method and direct human observer. These classification schemes are then used to perform gender prediction on facial contours. The final conclusion for the experiments is that MEM found correspondence points built classification scheme conveys a relatively more accurate gender prediction result. Although, we have explored the potential of our proposed method to some extent, this is not the end of the research for this topic. The future work is also clearly stated which includes more validations on various 3D datasets; discrimination analysis between normal and abnormal subjects could be the direct application for the proposed algorithm, extension to model-building using appearance information, etc

Trinity College Bulletin, 2010-2011 (Catalogue Issue)

https://digitalrepository.trincoll.edu/bulletin/1561/thumbnail.jp