Marcelo Siqueira

SMI 2011: Full Paper: Template-based quadrilateral meshing

Generating quadrilateral meshes is a highly non-trivial task, as design decisions are frequently driven by specific application demands. Automatic techniques can optimize objective quality metrics, such as mesh regularity, orthogonality, alignment and adaptivity; however, they cannot make subjective design decisions. There are a few quad meshing approaches that offer some mechanisms to include the user in the mesh generation process; however, these techniques either require a large amount of user interaction or do not provide necessary or easy to use inputs. Here, we propose a template-based approach for generating quad-only meshes from triangle surfaces. Our approach offers a flexible mechanism to allow external input, through the definition of alignment features that are respected during the mesh generation process. While allowing user inputs to support subjective design decisions, our approach also takes into account objective quality metrics to produce semi-regular, quad-only meshes that align well to desired surface features.

Technical Section: A new construction of smooth surfaces from triangle meshes using parametric pseudo-manifolds

We introduce a new manifold-based construction for fitting a smooth surface to a triangle mesh of arbitrary topology. Our construction combines in novel ways most of the best features of previous constructions and, thus, it fills the gap left by them. We also introduce a theoretical framework that provides a sound justification for the correctness of our construction. Finally, we demonstrate the effectiveness of our manifold-based construction with a few concrete examples.

Making 3D Binary Digital Images Well-Composed

A 3D binary digital image is said to be well-composed if and only if the set of points in the faces shared by the voxels of foreground and background points of the image is a 2D manifold. Well-composed images enjoy important topological and geometric properties; in particular, there is only one type of connected component in any well-composed image, as 6-, 14-, 18-, and 26-connected components are equal. This implies that several algorithms used in computer vision, computer graphics, and image processing become simpler. For example, thinning algorithms do not suffer from the irreducible thickness problem if the image is well-composed, and the extraction of isosurfaces from well-composed images using the Marching Cubes (MC) algorithm or some of its enhanced variations can be simplified, as only six out of the fourteen canonical cases of cube-isosurface intersection can occur. In this paper, we introduce a new randomized algorithm for making 3D binary digital images that are not well-composed into well-composed ones. We also analyze the complexity and convergence of our algorithm, and present experimental evidence of its effectiveness when faced with practical medical imaging data.

The J1a triangulation: An adaptive triangulation in any dimension

Abstract Spatial sampling methods have acquired great popularity due to the number of applications that need to triangulate portions of space in various dimensions. One limitation of the current techniques is the handling of the final models, which are large, complex and need to register neighborhood relationships explicitly. Additionally, most techniques are limited to Euclidean bi-dimensional or tri-dimensional spaces and many do not handle adaptive refinement well. This work presents a novel method for spatial decomposition based on simplicial meshes (the J 1 a triangulation) that is generally defined for Euclidean spaces of any dimension and is intrinsically adaptive. Additionally, it offers algebraic mechanisms for the decomposition itself and for indexing of neighbors that allow to recover all the information on the resulting mesh via a set of rules. With these mechanisms it is possible to save storage space by calculating the needed information instead of storing it.

CONSTRAINED QUADRILATERAL MESHES OF BOUNDED SIZE

We introduce a new algorithm to convert triangular meshes of polygonal regions, with or without holes, into strictly convex quadrilateral meshes of small bounded size. Our algorithm includes all vertices of the triangular mesh in the quadrilateral mesh, but may add extra vertices (called Steiner points). We show that if the input triangular mesh has t triangles, our algorithm produces a mesh with at most quadrilaterals by adding at most t+2 Steiner points, one of which may be placed outside the triangular mesh domain. We also describe an extension of our algorithm to convert constrained triangular meshes into constrained quadrilateral ones. We show that if the input constrained triangular mesh has t triangles and its dual graph has h connected components, the resulting constrained quadrilateral mesh has at most quadrilaterals and at most t+3h Steiner points, one of which may be placed outside the triangular mesh domain. Examples of meshes generated by our algorithm, and an evaluation of the quality of these meshes with respect to a quadrilateral shape quality criterion are presented as well.

Technical Section: Adaptive multi-chart and multiresolution mesh representation

In this paper, we present an adaptive multi-chart and multiresolution mesh representation suitable for both the CPU and the GPU. We build our representation by simplifying a dense-polygon mesh to a base mesh and storing the original geometry in an atlas structure. For both simplification and resolution control, we extend a hierarchical method based on stellar operators to the GPU context. During simplification, we compute local parametrizations to generate charts and an atlas structure to be used later in multiresolution management. Unlike previous approaches, we employ the simplified mesh as our base domain in a novel atlas descriptor combined with a specialized halfedge data structure, achieving superior geometric accuracy while adding a low additional storage. Finally, we show that our mesh representation can be used to adaptively control the mesh resolution in the CPU and the GPU at the same time in a broad range of applications, from mesh editing to rendering.

Template-based quadrilateral mesh generation from imaging data

This paper describes a novel template-based meshing approach for generating good quality quadrilateral meshes from 2D digital images. This approach builds upon an existing image-based mesh generation technique called Imeshp, which enables us to create a segmented triangle mesh from an image without the need for an image segmentation step. Our approach generates a quadrilateral mesh using an indirect scheme, which converts the segmented triangle mesh created by the initial steps of the Imesh technique into a quadrilateral one. The triangle-to-quadrilateral conversion makes use of template meshes of triangles. To ensure good element quality, the conversion step is followed by a smoothing step, which is based on a new optimization-based procedure. We show several examples of meshes generated by our approach, and present a thorough experimental evaluation of the quality of the meshes given as examples.

Topological Well-Composedness and Glamorous Glue: A Digital Gluing Algorithm for Topologically Constrained Front Propagation

We propose a new approach to front propagation algorithms based on a topological variant of well-composedness which contrasts with previous methods based on simple point detection. This provides for a theoretical justification, based on the digital Jordan separation theorem, for digitally “gluing” evolved well-composed objects separated by well-composed curves or surfaces. Additionally, our framework can be extended to more relaxed topologically constrained algorithms based on multisimple points. For both methods this framework has the additional benefit of obviating the requirement for both a user-specified connectivity and a topologically-consistent marching cubes/squares algorithm in meshing the resulting segmentation.

Template-Based Remeshing for Image Decomposition

This paper presents a novel quad-based remeshing scheme, which can be regarded as a replacement for the triangle-based improvement step of an existing image-based mesh generation technique called Imesh. This remeshing scheme makes it possible for the algorithm to generate good quality quadrilateral meshes directly from imaging data. The extended algorithm combines two ingredients: (1) a template-based triangulation-to-quadrangulation conversion strategy and (2) an optimization-based smoothing procedure. Examples of meshes generated by the extended algorithm, and an evaluation of the quality of those meshes are presented as well.

Good Random Multi-Triangulation of Surfaces

We introduce the Hierarchical Poisson Disk Sampling Multi-Triangulation (HPDS-MT) of surfaces, a novel structure that combines the power of multi-triangulation (MT) with the benefits of Hierarchical Poisson Disk Sampling (HPDS). MT is a general framework for representing surfaces through variable resolution triangle meshes, while HPDS is a well-spaced random distribution with blue noise characteristics. The distinguishing feature of the HPDS-MT is its ability to extract adaptive meshes whose triangles are guaranteed to have good shape quality. The key idea behind the HPDS-MT is a preprocessed hierarchy of points, which is used in the construction of a MT via incremental simplification. In addition to proving theoretical properties on the shape quality of the triangle meshes extracted by the HPDS-MT, we provide an implementation that computes the HPDS-MT with high accuracy. Our results confirm the theoretical guarantees and outperform similar methods. We also prove that the Hausdorff distance between the original surface and any (extracted) adaptive mesh is bounded by the sampling distribution of the radii of Poisson-disks over the surface. Finally, we illustrate the advantages of the HPDS-MT in some typical problems of geometry processing.