168 research outputs found
Geometric Surface Processing and Virtual Modeling
In this work we focus on two main topics "Geometric Surface Processing" and "Virtual Modeling". The inspiration and coordination for most of the research work contained in the thesis has been driven by the project New Interactive and Innovative Technologies for CAD (NIIT4CAD), funded by the European Eurostars Programme. NIIT4CAD has the ambitious aim of overcoming the limitations of the traditional approach to surface modeling of current 3D CAD systems by introducing new methodologies and technologies based on subdivision surfaces
in a new virtual modeling framework. These innovations will allow designers and engineers to transform quickly and intuitively an idea of shape in a high-quality geometrical model suited for engineering and manufacturing purposes.
One of the objective of the thesis is indeed the reconstruction and modeling of surfaces, representing arbitrary topology objects, starting from 3D irregular curve networks acquired through an ad-hoc smart-pen device.
The thesis is organized in two main parts: "Geometric Surface Processing" and "Virtual Modeling". During the development of the geometric pipeline in our Virtual Modeling system, we faced many challenges that captured our interest and opened new areas of research and experimentation.
In the first part, we present these theories and some applications to Geometric Surface Processing.
This allowed us to better formalize and give a broader understanding on some of the techniques used in our latest advancements on virtual modeling and surface reconstruction.
The research on both topics led to important results that have been published and presented in articles and conferences of international relevance
A comparison of hole-filling methods in 3D
This paper presents a review of the most relevant current techniques that deal with hole-filling in 3D models. Contrary to earlier reports, which approach mesh repairing in a sparse and global manner, the objective of this review is twofold. First, a specific and comprehensive review of hole-filling techniques (as a relevant part in the field of mesh repairing) is carried out. We present a brief summary of each technique with attention paid to its algorithmic essence, main contributions and limitations. Second, a solid comparison between 34 methods is established. To do this, we define 19 possible meaningful features and properties that can be found in a generic hole-filling process. Then, we use these features to assess the virtues and deficiencies of the method and to build comparative tables. The purpose of this review is to make a comparative hole-filling state-of-the-art available to researchers, showing pros and cons in a common framework.• Ministerio de Economía y Competitividad: Proyecto DPI2013-43344-R (I+D+i)
• Gobierno de Castilla-La Mancha: Proyecto PEII-2014-017-PpeerReviewe
Implicit meshes:unifying implicit and explicit surface representations for 3D reconstruction and tracking
This thesis proposes novel ways both to represent the static surfaces, and to parameterize their deformations. This can be used both by automated algorithms for efficient 3–D shape reconstruction, and by graphics designers for editing and animation. Deformable 3–D models can be represented either as traditional explicit surfaces, such as triangulated meshes, or as implicit surfaces. Explicit surfaces are widely accepted because they are simple to deform and render, however fitting them involves minimizing a non-differentiable distance function. By contrast, implicit surfaces allow fitting by minimizing a differentiable algebraic distance, but they are harder to meaningfully deform and render. Here we propose a method that combines the strength of both representations to avoid their drawbacks, and in this way build robust surface representation, called implicit mesh, suitable for automated shape recovery from video sequences. This surface representation lets us automatically detect and exploit silhouette constraints in uncontrolled environments that may involve occlusions and changing or cluttered backgrounds, which limit the applicability of most silhouette based methods. We advocate the use of Dirichlet Free Form Deformation (DFFD) as generic surface deformation technique that can be used to parameterize objects of arbitrary geometry defined as explicit meshes. It is based on the small set of control points and the generalized interpolant. Control points become model parameters and their change causes model's shape modification. Using such parameterization the problem dimensionality can be dramatically reduced, which is desirable property for most optimization algorithms, thus makes DFFD good tool for automated fitting. Combining DFFD as a generic parameterization method for explicit surfaces and implicit meshes as a generic surface representation we obtained a powerfull tool for automated shape recovery from images. However, we also argue that any other avaliable surface parameterization can be used. We demonstrate the applicability of our technique to 3–D reconstruction of the human upper-body including – face, neck and shoulders, and the human ear, from noisy stereo and silhouette data. We also reconstruct the shape of a high resolution human faces parametrized in terms of a Principal Component Analysis model from interest points and automatically detected silhouettes. Tracking of deformable objects using implicit meshes from silhouettes and interest points in monocular sequences is shown in following two examples: Modeling the deformations of a piece of paper represented by an ordinary triangulated mesh; tracking a person's shoulders whose deformations are expressed in terms of Dirichlet Free Form Deformations
Subdivision Shell Elements with Anisotropic Growth
A thin shell finite element approach based on Loop's subdivision surfaces is
proposed, capable of dealing with large deformations and anisotropic growth. To
this end, the Kirchhoff-Love theory of thin shells is derived and extended to
allow for arbitrary in-plane growth. The simplicity and computational
efficiency of the subdivision thin shell elements is outstanding, which is
demonstrated on a few standard loading benchmarks. With this powerful tool at
hand, we demonstrate the broad range of possible applications by numerical
solution of several growth scenarios, ranging from the uniform growth of a
sphere, to boundary instabilities induced by large anisotropic growth. Finally,
it is shown that the problem of a slowly and uniformly growing sheet confined
in a fixed hollow sphere is equivalent to the inverse process where a sheet of
fixed size is slowly crumpled in a shrinking hollow sphere in the frictionless,
quasi-static, elastic limit.Comment: 20 pages, 12 figures, 1 tabl
Surface Reconstruction From 3D Point Clouds
The triangulation of a point cloud of a 3D object is a complex problem, since it
depends on the complexity of the shape of such object, as well as on the density
of points generated by a specific scanner.
In the literature, there are essentially two approaches to the reconstruction of
surfaces from point clouds: interpolation and approximation. In general, interpolation
approaches are associated with simplicial methods; that is, methods
that directly generate a triangle mesh from a point cloud. On the other hand,
approximation approaches generate a global implicit function — that represents
an implicit surface — from local shape functions, then generating a triangulation
of such implicit surface.
The simplicial methods are divided into two families: Delaunay and mesh growing.
Bearing in mind that the first of the methods presented in this dissertation
falls under the category of mesh growing methods, let us focus our attention
for now on these methods. One of the biggest problems with these methods is
that, in general, they are based on the establishment of dihedral angle bounds
between adjacent triangles, as needed to make the decision on which triangle
to add to the expansion mesh front. Typically, other bounds are also used for
the internal angles of each triangle. In the course of this dissertation, we will
see how this problem was solved.
The second algorithm introduced in this dissertation is also a simplicial method
but does not fit into any of the two families mentioned above, which makes
us think that we are in the presence of a new family: triangulation based on
the atlas of charts or triangle stars. This algorithm generates an atlas of the
surface that consists of overlapping stars of triangles, that is, one produces a
total surface coverage, thus solving one of the common problems of this family
of direct triangulation methods, which is the appearance of holes or incomplete
triangulation of the surface.
The third algorithm refers to an implicit method, but, unlike other implicit
methods, it uses an interpolation approach. That is, the local shape functions
interpolate the points of the cloud. It is, perhaps, one of a few implicit methods
that we can find in the literature that interpolates all points of the cloud.
Therefore, one of the biggest problems of the implicit methods is solved, which
has to do with the smoothing of the surface sharp features resulting from the blending of the local functions into the global function.
What is common to the three methods is the interpolation approach, either in
simple or implicit methods, that is, the linearization of the surface subject to
reconstruction. As will be seen, the linearization of the neighborhood of each
point allows us to solve several problems posed to the surface reconstruction
algorithms, namely: point sub‐sampling, non‐uniform sampling, as well as sharp
features.A triangulação de uma nuvem de pontos de um objeto 3D é um problema complexo,
uma vez que depende da complexidade da forma desse objeto, assim
como da densidade dos pontos extraídos desse objeto através de um scanner 3D
particular.
Na literatura, existem essencialmente duas abordagens na reconstrução de superfícies
a partir de nuvens de pontos: interpolação e aproximação. Em geral, as
abordagens de interpolação estão associadas aos métodos simpliciais, ou seja,
a métodos que geram diretamente uma malha de triângulos a partir de uma
nuvem de pontos. Por outro lado, as abordagens de aproximação estão habitualmente
associadas à geração de uma função implícita global —que representa
uma superfície implícita— a partir de funções locais de forma, para em seguida
gerar uma triangulação da dita superfície implícita.
Os métodos simpliciais dividem‐se em duas famílias: triangulação de Delaunay
e triangulação baseada em crescimento progressivo da triangulação (i.e., mesh
growing). Tendo em conta que o primeiro dos métodos apresentados nesta dissertação
se enquadra na categoria de métodos de crescimento progressivo, foquemos
a nossa atenção por ora nestes métodos. Um dos maiores problemas
destes métodos é que, em geral, se baseiam no estabelecimento de limites de
ângulos diédricos (i.e., dihedral angle bounds) entre triângulos adjacentes, para
assim tomar a decisão sobre qual triângulo acrescentar à frente de expansão da
malha. Tipicamente, também se usam limites para os ângulos internos de cada
triângulo. No decorrer desta dissertação veremos como é que este problema foi
resolvido.
O segundo algoritmo introduzido nesta dissertação também é um método simplicial,
mas não se enquadra em nenhuma das duas famílias acima referidas, o que
nos faz pensar que estaremos na presença de uma nova família: triangulação
baseada em atlas de vizinhanças sobrepostas (i.e., atlas of charts) ou estrelas
de triângulos (i.e., triangle star). Este algoritmo gera um atlas da superfície
que é constituído por estrelas sobrepostas de triângulos, ou seja, produz‐se a
cobertura total da superfície, resolvendo assim um dos problemas comuns desta
família de métodos de triangulação direta que é o do surgimento de furos ou de
triangulação incompleta da superfície.
O terceiro algoritmo refere‐se a um método implícito, mas, ao invés de grande parte dos métodos implícitos, utiliza uma abordagem de interpolação. Ou seja,
as funções locais de forma interpolam os pontos da nuvem. É, talvez, um dos
poucos métodos implícitos que podemos encontrar na literatura que interpola
todos os pontos da nuvem. Desta forma resolve‐se um dos maiores problemas dos
métodos implícitos que é o do arredondamento de forma resultante do blending
das funções locais que geram a função global, em particular ao longo dos vincos
da superfície (i.e., sharp features).
O que é comum aos três métodos é a abordagem de interpolação, quer em
métodos simpliciais quer em métodos implícitos, ou seja a linearização da superfície
sujeita a reconstrução. Como se verá, a linearização da vizinhança de
cada ponto permite‐nos resolver vários problemas colocados aos algoritmos de
reconstrução de superfícies, nomeadamente: sub‐amostragem de pontos (point
sub‐sampling), amostragem não uniforme (non‐uniform sampling), bem como
formas vincadas (sharp features)
A framework for hull form reverse engineering and geometry integration into numerical simulations
The thesis presents a ship hull form specific reverse engineering and CAD integration framework. The reverse engineering part proposes three alternative suitable reconstruction approaches namely curves network, direct surface fitting, and triangulated surface reconstruction. The CAD integration part includes surface healing, region identification, and domain preparation strategies which used to adapt the CAD model to downstream application requirements. In general, the developed framework bridges a point cloud and a CAD model obtained from IGES and STL file into downstream applications
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