381 research outputs found
Feature correspondences From Multiple Views of Coplanar Ellipses
International audienceWe address the problem of feature correspondences in images of coplanar ellipses with objective to benefit of robust ellipse fitting algorithm. The main difficulty is the lack of projective invariant points immediately available. Therefore, our key idea is to construct virtual line and point features using the property of tangent invariance under perspective projection. The proposed method requires first a robust detection of ellipse edge points to fit a parametric model on each ellipse. The feature lines are then obtained by computing the 4 bitangents to each couple of ellipses. The points are derived by considering the tangent points and the intersection points between bitangents. Results of experimental studies are presented to demonstrate the reliability and robustness of the feature extraction process. Subpixel accuracy is easily achieved. A real application to camera self-calibration is also described
Direct Least-Squares Ellipse Fitting
Many biological and astronomical forms can be best represented by ellipses. While some more complex curves might represent the shape more accurately, ellipses have the advantage that they are easily parameterised and define the location, orientation and dimensions of the data more clearly. In this paper, we present a method of direct least-squares ellipse fitting by solving a generalised eigensystem. This is more efficient and more accurate than many alternative approaches to the ellipse-fitting problem such as fuzzy c-shells clustering and Hough transforms. This method was developed for human body modelling as part of a larger project to design a marker-free gait analysis system which is being undertaken at the National Rehabilitation Hospital, Dublin
Angular variation as a monocular cue for spatial percepcion
Monocular cues are spatial sensory inputs which are picked up exclusively from one eye. They are in majority static features that
provide depth information and are extensively used in graphic art to create realistic representations of a scene. Since the spatial
information contained in these cues is picked up from the retinal image, the existence of a link between it and the theory of direct
perception can be conveniently assumed. According to this theory, spatial information of an environment is directly contained in the
optic array. Thus, this assumption makes possible the modeling of visual perception processes through computational approaches.
In this thesis, angular variation is considered as a monocular cue, and the concept of direct perception is adopted by a computer
vision approach that considers it as a suitable principle from which innovative techniques to calculate spatial information can be
developed.
The expected spatial information to be obtained from this monocular cue is the position and orientation of an object with respect to
the observer, which in computer vision is a well known field of research called 2D-3D pose estimation. In this thesis, the attempt to
establish the angular variation as a monocular cue and thus the achievement of a computational approach to direct perception is
carried out by the development of a set of pose estimation methods. Parting from conventional strategies to solve the pose
estimation problem, a first approach imposes constraint equations to relate object and image features. In this sense, two algorithms
based on a simple line rotation motion analysis were developed. These algorithms successfully provide pose information; however,
they depend strongly on scene data conditions. To overcome this limitation, a second approach inspired in the biological processes
performed by the human visual system was developed. It is based in the proper content of the image and defines a computational
approach to direct perception.
The set of developed algorithms analyzes the visual properties provided by angular variations. The aim is to gather valuable data
from which spatial information can be obtained and used to emulate a visual perception process by establishing a 2D-3D metric
relation. Since it is considered fundamental in the visual-motor coordination and consequently essential to interact with the
environment, a significant cognitive effect is produced by the application of the developed computational approach in environments
mediated by technology. In this work, this cognitive effect is demonstrated by an experimental study where a number of participants
were asked to complete an action-perception task. The main purpose of the study was to analyze the visual guided behavior in
teleoperation and the cognitive effect caused by the addition of 3D information. The results presented a significant influence of the
3D aid in the skill improvement, which showed an enhancement of the sense of presence.Las señales monoculares son entradas sensoriales capturadas exclusivamente por un
solo ojo que ayudan a la percepción de distancia o espacio. Son en su mayoría
características estáticas que proveen información de profundidad y son muy
utilizadas en arte gráfico para crear apariencias reales de una escena. Dado que la
información espacial contenida en dichas señales son extraídas de la retina, la
existencia de una relación entre esta extracción de información y la teoría de
percepción directa puede ser convenientemente asumida. De acuerdo a esta teoría, la
información espacial de todo le que vemos está directamente contenido en el arreglo
óptico. Por lo tanto, esta suposición hace posible el modelado de procesos de
percepción visual a través de enfoques computacionales. En esta tesis doctoral, la
variación angular es considerada como una señal monocular, y el concepto de
percepción directa adoptado por un enfoque basado en algoritmos de visión por
computador que lo consideran un principio apropiado para el desarrollo de nuevas
técnicas de cálculo de información espacial.
La información espacial esperada a obtener de esta señal monocular es la posición y
orientación de un objeto con respecto al observador, lo cual en visión por computador
es un conocido campo de investigación llamado estimación de la pose 2D-3D. En esta
tesis doctoral, establecer la variación angular como señal monocular y conseguir un
modelo matemático que describa la percepción directa, se lleva a cabo mediante el
desarrollo de un grupo de métodos de estimación de la pose. Partiendo de estrategias
convencionales, un primer enfoque implanta restricciones geométricas en ecuaciones
para relacionar características del objeto y la imagen. En este caso, dos algoritmos
basados en el análisis de movimientos de rotación de una línea recta fueron
desarrollados. Estos algoritmos exitosamente proveen información de la pose. Sin
embargo, dependen fuertemente de condiciones de la escena. Para superar esta
limitación, un segundo enfoque inspirado en los procesos biológicos ejecutados por el
sistema visual humano fue desarrollado. Está basado en el propio contenido de la
imagen y define un enfoque computacional a la percepción directa.
El grupo de algoritmos desarrollados analiza las propiedades visuales suministradas
por variaciones angulares. El propósito principal es el de reunir datos de importancia
con los cuales la información espacial pueda ser obtenida y utilizada para emular
procesos de percepción visual mediante el establecimiento de relaciones métricas 2D-
3D. Debido a que dicha relación es considerada fundamental en la coordinación
visuomotora y consecuentemente esencial para interactuar con lo que nos rodea, un
efecto cognitivo significativo puede ser producido por la aplicación de métodos de
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estimación de pose en entornos mediados tecnológicamente. En esta tesis doctoral, este
efecto cognitivo ha sido demostrado por un estudio experimental en el cual un número
de participantes fueron invitados a ejecutar una tarea de acción-percepción. El
propósito principal de este estudio fue el análisis de la conducta guiada visualmente en
teleoperación y el efecto cognitivo causado por la inclusión de información 3D. Los
resultados han presentado una influencia notable de la ayuda 3D en la mejora de la
habilidad, así como un aumento de la sensación de presencia
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On the capture and representation of fonts
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The commercial need to capture, process and represent the shape and form of an outline has lead to the development of a number of spline routines. These use a mathematical curve format that approximates the contours of a given shape. The modelled outline lends itself to be used on, and for, a variety of purposes. These include graphic screens, laser printers and numerically controlled machines. The latter can be employed for cutting foil, metal. plastic and stone. One of the most widely used software design packages has been the lKARUS system. This, developed by URW of Hamburg (Gennany), employs a number of mathematical descriptions that facilitate the process of both modelling and representation of font characters. It uses a variety of curve formats, including Bezier cubics, general conics and parabolics. The work reported in this dissertation focuses on developing improved techniques, primarily. for the lKARUS system. This includes two algorithms
which allow a Bezier cubic description, two for a general conic representation and, yet another, two for the parabolic case. In addition, a number of algorithms are presented which promote conversions between these mathematical forms; for example, Bezier cubics to a general conic form. Furthennore, algorithms are developed to assist the process of rasterising both cubic and quadratic arcs.This study was partly funded by the Science and Education Research Council (SERC)
New Confocal Hyperbola-based Ellipse Fitting with Applications to Estimating Parameters of Mechanical Pipes from Point Clouds
This manuscript presents a new method for fitting ellipses to two-dimensional
data using the confocal hyperbola approximation to the geometric distance of
points to ellipses. The proposed method was evaluated and compared to
established methods on simulated and real-world datasets. First, it was
revealed that the confocal hyperbola distance considerably outperforms other
distance approximations such as algebraic and Sampson. Next, the proposed
ellipse fitting method was compared with five reliable and established methods
proposed by Halir, Taubin, Kanatani, Ahn and Szpak. The performance of each
method as a function of rotation, aspect ratio, noise, and arc-length were
examined. It was observed that the proposed ellipse fitting method achieved
almost identical results (and in some cases better) than the gold standard
geometric method of Ahn and outperformed the remaining methods in all
simulation experiments. Finally, the proposed method outperformed the
considered ellipse fitting methods in estimating the geometric parameters of
cylindrical mechanical pipes from point clouds. The results of the experiments
show that the confocal hyperbola is an excellent approximation to the true
geometric distance and produces reliable and accurate ellipse fitting in
practical settings
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