3D Surface Mesh Research Articles

Quantitative methods in archaeoseismology

Within the multidisciplinary field of archaeoseismology, quantitative methods have begun to be utilized more prevalently. This paper proposes a scheme of applying quantitative models to test the seismogenic hypothesis of observed damage and gives examples from field cases. The combination of 3D structural models of buildings or their remains based in part on phase shift laserscanner measurements combined with high-resolution digital images allows the construction of a damage and/or deformation inventory and assists archaeological work during an excavation. 3D surface meshes derived from the same scan data are the basis for Finite or Discrete Element models of the structures. The effect of site-specific earthquake-related ground motions, other natural causes, and anthropogenic influences are simulated and ultimately compared with the damage inventory. However, due to the high level of complexity of the problems, definite answers cannot always be achieved.

The spiral facets: A unified framework for the analysis and description of 3D facial mesh surface

In this paper, we describe an original topological framework for encoding 3D facial triangular mesh surface. We derive shape information from the triangular mesh surface by exploiting specific arrangements of facets in the model. We describe the foundations of the framework and show how it can be employed in several original applications including face landmark detection, frontal face extraction, face orientation and facial surface representation. We validate the framework through experimentation with raw 3D face mesh surfaces and demonstrate that the model allows simpler implementation, more compact representation and encompasses rich shape information that can be usefully deployed both locally and globally across the face in comparison to other standard representations.

Möbius Transformations For Global Intrinsic Symmetry Analysis

AbstractThe goal of our work is to develop an algorithm for automatic and robust detection of global intrinsic symmetries in 3D surface meshes. Our approach is based on two core observations. First, symmetry invariant point sets can be detected robustly using critical points of the Average Geodesic Distance (AGD) function. Second, intrinsic symmetries are self‐isometries of surfaces and as such are contained in the low dimensional group of Möbius transformations. Based on these observations, we propose an algorithm that: 1) generates a set of symmetric points by detecting critical points of the AGD function, 2) enumerates small subsets of those feature points to generate candidate Möbius transformations, and 3) selects among those candidate Möbius transformations the one(s) that best map the surface onto itself. The main advantages of this algorithm stem from the stability of the AGD in predicting potential symmetric point features and the low dimensionality of the Möbius group for enumerating potential self‐mappings. During experiments with a benchmark set of meshes augmented with human‐specified symmetric correspondences, we find that the algorithm is able to find intrinsic symmetries for a wide variety of object types with moderate deviations from perfect symmetry.

Developability Optimization Algorithm for 3D Mesh Surfaces

Developable surface has zero Gaussian curvature at every point and has lots of good properties.It has been widely used in various applications in industry.Therefore,it is practically useful and important to approximate mesh surfaces using developable surfaces or near-developable surfaces.This paper presents an efficient algorithm for generating a near developable mesh surface to approximate a given mesh surface as close as possible while preserving the local structures of the surface.First,the initial mesh is obtained by using the least-norm method.The initial mesh has good developability property but it does not preserve the local structure well.Then the as-rigid-as-possible(ARAP) approach is used to optimize the initial mesh by preserving the local structures of the original mesh.This paper proposes two methods,i.e.the cell-based and the triangle-based,to preserve the local structures in the ARAP approach.Both methods work well in above algorithm.The initial mesh and the ARAP optimization can be applied in an iterative way.Experimental results show that the algorithm is convergent has obtained better results with less iterations than the previous methods.

A benchmark for 3D mesh segmentation

This paper describes a benchmark for evaluation of 3D mesh segmentation salgorithms. The benchmark comprises a data set with 4,300 manually generated segmentations for 380 surface meshes of 19 different object categories, and it includes software for analyzing 11 geometric properties of segmentations and producing 4 quantitative metrics for comparison of segmentations. The paper investigates the design decisions made in building the benchmark, analyzes properties of human-generated and computer-generated segmentations, and provides quantitative comparisons of 7 recently published mesh segmentation algorithms. Our results suggest that people are remarkably consistent in the way that they segment most 3D surface meshes, that no one automatic segmentation algorithm is better than the others for all types of objects, and that algorithms based on non-local shape features seem to produce segmentations that most closely resemble ones made by humans.

YIA Abstracts: Best abstracts on clinical studies

YIA Abstracts: Best abstracts on clinical studies

Direct sampling on surfaces for high quality remeshing

Isotropic point distribution is crucial in remeshing process to generate a high-quality mesh. In this paper, we present a novel algorithm of isotropic sampling on two-manifold mesh surface. Our main contribution lies in the successful generalization of a 2D fast Poisson disk sampling algorithm, which makes it able to sample directly 3D mesh surfaces, including feature edges. We adopt geodesic distance as the distance metric for sampling algorithm in 3D to better capture the geometry information. Given a density function over the surface, we derive a close analytic form of the available boundary, which makes our algorithm support efficient adaptive sampling. To further improve the isotropy of point distribution, Lloyd relaxation is performed locally to optimize the location of sampling points. The whole process guarantees that new vertices lie on the original surface. Mutual tessellation is utilized to reconstruct the connectivity of new vertices, which guarantees the fidelity and validity of topology. Experiments show that our algorithm is able to remesh an arbitrary closed manifold into a high-quality mesh with large minimal angles and small number of irregular vertices.

Pattern of hippocampal shape and volume differences in blind subjects

Numerous studies in animals and humans have shown that the hippocampus (HP) is involved in spatial navigation and memory. Blind subjects, in particular, must memorize extensive information to compensate for their lack of immediate updating of spatial information. Increased demands on spatial cognition and memory may be associated with functional and structural HP plasticity.Here we examined local size and shape differences in the HP of blind and sighted individuals. A 3D parametric mesh surface was generated to represent right and left HPs in each individual, based on manual segmentations of 3D volumetric T1-weighted MR images of 22 blind subjects and 28 matched controls. Using a new surface mapping algorithm described in (Shi, Y., Thompson, P.M., de Zubicaray, G.I., Rose, S.E., Tu, Z., Dinov, I., Toga, A.W., Direct mapping of hippocampal surfaces with intrinsic shape context, NeuroImage, Available online May 24, (In Press).), we created an average hippocampal surface for the controls, and computed its normal distance to each individual surface. Statistical maps were created to visualize systematic anatomical differences between groups, and randomization tests were performed to correct for multiple comparisons.In both scaled and unscaled data, the anterior right HP was significantly larger, and the posterior right HP significantly smaller in blind individuals. No significant differences were found for left HP. These differences may reflect adaptive responses to sensory deprivation, and/or increased functional demands on memory systems. They offer a neuroanatomical substrate for future correlations with measures of navigation performance or functional activations related to variations in cognitive strategies.

Characterization of 3D shape parts for semantic annotation

3D content stored in big databases or shared on the Internet is a precious resource for several applications, but unfortunately it risks being underexploited due to the difficulty of retrieving it efficiently. In this paper we describe a system called the “ShapeAnnotator” through which it is possible to perform non-trivial segmentations of 3D surface meshes and annotate the detected parts through concepts expressed by an ontology. Each part is connected to an instance that can be stored in a knowledge base to ease the retrieval process based on semantics. Through an intuitive interface, users create such instances by simply selecting proper classes in the ontology; attributes and relations with other instances can be computed automatically based on a customizable analysis of the underlying topology and geometry of the parts. We show how our part-based annotation framework can be used in two scenarios, namely for the creation of avatars in emerging Internet-based virtual worlds, and for product design in e-manufacturing.

Randomized cuts for 3D mesh analysis

The goal of this paper is to investigate a new shape analysis method based on randomized cuts of 3D surface meshes. The general strategy is to generate a random set of mesh segmentations and then to measure how often each edge of the mesh lies on a segmentation boundary in the randomized set. The resulting "partition function" defined on edges provides a continuous measure of where natural part boundaries occur in a mesh, and the set of "most consistent cuts" provides a stable list of global shape features. The paper describes methods for generating random distributions of mesh segmentations, studies sensitivity of the resulting partition functions to noise, tessellation, pose, and intra-class shape variations, and investigates applications in mesh visualization, segmentation, deformation, and registration.

Mapping local hippocampal changes in Alzheimer's disease and normal ageing with MRI at 3 Tesla

Histological studies have suggested differing involvement of the hippocampal subfields in ageing and in Alzheimer's disease. The aim of this study was to assess in vivo local hippocampal changes in ageing and Alzheimer's disease based on high resolution MRI at 3 Tesla. T(1)-weighted images were acquired from 19 Alzheimer's disease patients [age 76 +/- 6 years, three males, Mini-Mental State Examination 13 +/- 4] and 19 controls (age 74 +/- 5 years, 11 males, Mini-Mental State Examination 29 +/- 1). The hippocampal formation was isolated by manual tracing. Radial atrophy mapping was used to assess group differences and correlations by averaging hippocampal shapes across subjects using 3D parametric surface mesh models. Percentage difference, Pearson's r, and significance maps were produced. Hippocampal volumes were inversely correlated with age in older healthy controls (r = 0.56 and 0.6 to the right and left, respectively, P < 0.05, corresponding to 14% lower volume for every 10 years of older age from ages 65 to 85 years). Ageing-associated atrophy mapped to medial and lateral areas of the tail and body corresponding to the CA1 subfield and ventral areas of the head corresponding to the presubiculum. Significantly increased volume with older age mapped to a few small spots mainly located to the CA1 sector of the right hippocampus. Volumes were 35% and 30% smaller in Alzheimer's disease patients to the right and left (P < 0.0005). Alzheimer's disease-associated atrophy mapped not only to CA1 areas of the body and tail corresponding to those also associated with age, but also to dorsal CA1 areas of the head unaffected by age. Regions corresponding to the CA2-3 fields were relatively spared in both ageing and Alzheimer's disease. Hippocampal atrophy in Alzheimer's disease maps to areas in the body and tail that partly overlap those affected by normal ageing. Specific areas in the anterior and dorsal CA1 subfield involved in Alzheimer's disease were not in normal ageing. These patterns might relate to differential neural systems involved in Alzheimer's disease and ageing.

The effects of multiview depth video compression on multiview rendering

This article investigates the interaction between different techniques for depth compression and view synthesis rendering with multiview video plus scene depth data. Two different approaches for depth coding are compared, namely H.264/MVC, using temporal and inter-view reference images for efficient prediction, and the novel platelet-based coding algorithm, characterized by being adapted to the special characteristics of depth-images. Since depth-images are a 2D representation of the 3D scene geometry, depth-image errors lead to geometry distortions. Therefore, the influence of geometry distortions resulting from coding artifacts is evaluated for both coding approaches in two different ways. First, the variation of 3D surface meshes is analyzed using the Hausdorff distance and second, the distortion is evaluated for 2D view synthesis rendering, where color and depth information are used together to render virtual intermediate camera views of the scene. The results show that—although its rate-distortion (R-D) performance is worse—platelet-based depth coding outperforms H.264, due to improved sharp edge preservation. Therefore, depth coding needs to be evaluated with respect to geometry distortions.

Accuracy and repeatability of cone-beam computed tomography (CBCT) measurements used in the determination of facial indices in the laboratory setup

To assess the three dimensional (3D) surface accuracy of a phantom's face acquired from a cone-beam computed tomography (CBCT) scan and to determine the reliability of selected cephalometric measurements performed with Maxilim software (Medicim N.V., Mechelen, Belgium). A mannequin head was imaged with a CBCT (I-CAT, Imaging Sciences International, Inc., Hatfield, USA). The data were used to produce 3D surface meshes (Maxilim and Mimics, Materialise N.V., Leuven, Belgium) which were compared with an optical surface scan of the head using Focus Inspection software (Metris N.V., Leuven, Belgium). The intra- and inter-observer reliability for the measurement of distances between facial landmarks with Maxilim 3D cephalometry were determined by calculating Pearson correlation coefficients and intraclass correlation (ICC). The Dahlberg formula was used to assess the method error (ME). (1) The maximal range of the 3D mesh deviations was 1.9 mm for Maxilim, and 1.8mm for Mimics segmentation. (2) Test-retest and inter-observer reliability were high; Pearson's correlation coefficient was 1.000 and the ICC was 0.9998. The ME of the vertical measurements was a little larger than that calculated for the width measurements. Maximum ME was 1.33 mm. The 3D surface accuracy of CBCT scans segmented with Maxilim and Mimics software is high. Maxilim also shows satisfactory intra- and inter-assessor reliability for measurement of distances on a rigid facial surface.

SU-GG-T-56: Planning Target Volume Adaptation Using Convex Hull of CTVs for Cervix Cancer Patients

Purpose: Adaptive IMRT planning studies have shown that intra‐ and inter‐fractional organ motion can significantly decrease the coverage of the clinical target volume (CTV) for cervix cancer patients. Adaptive mid‐treatment re‐planning was effective in minimizing CTV underdosage, but this strategy only worked for patients with consistent bladder filling. This study investigated planning target volume (PTV) adaptation using a convex hull (CH) technique for patients whose bladder filling is variable over the course of radiation treatment.Method and Materials: Nine cervix cancer patients with variable bladder filling during the treatment were selected from 35 patients enrolled in an adaptive IMRT planning study. All patients were MR‐scanned once for planning and weekly during treatment. CTV and organs at risk (OAR) were contoured on each MR scan fused to planning CT with bony alignment. Contours were converted to 3D surface meshes for deformation analysis considering tissuebiomechanics. Two MR scans with full/empty bladder were identified and an adaptive PTV was found using a convex hull algorithm in the research planning software. IMRT plans were generated on the CH PTV and accumulated dose on deformed organs were simulated. Results: The average volume of CH PTV was 16% larger than that of small margin (3mm) PTV (477vs411cc). Most of the volume increase was found in the area of rectum where the concavity of the CTV was largest. The CH PTV had a non‐uniform margin around CTV representing patient‐specific CTV motion and deformation. The CH plan maintained target coverage but increased dose at OARs compared to adaptive mid‐treatment re‐planning. Discussion: Adaptive planning strategy using convex hull of CTVs demonstrates good target coverage for cervix cancer patients with variable bladder filling. Refindment of the CH to spare OARs might allow a reduction in critical organdose while still maintaining target coverage.

An extended advancing front technique for closed surfaces mesh generation

AbstractAn extended advancing front technique (AFT) with shift operations and Riemann metric named as shifting‐AFT is presented for finite element mesh generation on 3D surfaces, especially 3D closed surfaces. Riemann metric is used to govern the size and shape of the triangles in the parametric space. The shift operators are employed to insert a floating space between real space and parametric space during the 2D parametric space mesh generation. In the previous work of closed surface mesh generation, the virtual boundaries are adopted when mapping the closed surfaces into 2D open parametric domains. However, it may cause the mesh quality‐worsening problem. In order to overcome this problem, the AFT kernel is combined with the shift operator in this paper. The shifting‐AFT can generate high‐quality meshes and guarantee convergence in both open and closed surfaces. For the shifting‐AFT, it is not necessary to introduce virtual boundaries while meshing a closed surface; hence, the boundary discretization procedure is largely simplified, and moreover, better‐shaped triangles will be generated because there are no additional interior constraints yielded by virtual boundaries. Comparing with direct methods, the shifting‐AFT avoids costly and unstable 3D geometrical computations in the real space. Some examples presented in this paper have demonstrated the advantages of shift‐AFT in 3D surface mesh generation, especially for the closed surfaces. Copyright © 2007 John Wiley &amp; Sons, Ltd.

A robust backward search method based on walk‐through for point location on a 3D surface mesh

AbstractPoint location is one of the most basic searching problems in computational geometry. It has been largely studied on the aspect of query time in the worst case, and many methods have been proposed, such as counter clockwise wise search and barycentric coordinates search. However, most of them aim at the convex field. For a non‐convex problem, such as a concave field or a convex field with holes, these searching schemes may fail. The numerical experience shows that, even for a convex problem, the searching path may lead to an infinite loop for some special case and may not find the element containing the query point. In this paper, a robust backward search method based on Walk‐through algorithm is proposed to deal with the searching problems in non‐convex fields and to avoid the problems of infinite loop. Another important improvement is to locate the query point on a 3D surface mesh. Several examples demonstrate that the present method is efficient and robust for the workpieces of complex geometry. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Fast example-based surface texture synthesis via discrete optimization

We synthesize and animate general texture patterns over arbitrary 3D mesh surfaces. The animation is controlled by flow fields over the target mesh, and the texture can be arbitrary user input as long it satisfies the Markov-Random-Field assumptions. We achieve this by extending the texture optimization framework over 3D mesh surfaces. We propose an efficient discrete solver inspired by k-coherence search, allowing interactive flow texture animation while avoiding the blurry blending problem for the least square solver in previous work. Our technique has potential applications ranging from simulation, visualization, and special effects.

3D mapping of ventricular and corpus callosum abnormalities in HIV/AIDS

Objective: 40 million people worldwide are now infected with HIV/AIDS, an illness that often leads to rapidly progressing dementia and death. Even so, little is known about how AIDS affects the brain. Using computational anatomy techniques, we mapped how AIDS impacts the corpus callosum (CC) and ventricular system, two systems that show prominent changes on MRI. We (1) identified regions with greatest differences between AIDS patients and healthy controls and (2) correlated specific 3D patterns of structural differences with measures of immune system deterioration and cognitive decline. Methods: 51 3D brain MRI scans from 30 non-demented AIDS patients (age: 43.4 years ± 7.6 SD) and 21 HIV-seronegative controls (age: 39.5 years ± 12.2) were aligned to ICBM standard space. 3D surface mesh reconstructions of the lateral ventricles and CC were spatially averaged and compared across diagnostic groups. Structural alterations were correlated with viral load, T cell counts, and cognitive impairment. Results: Statistical maps revealed the 3D profile of ventricular expansion and callosal thinning in AIDS. Specific 3D ventricular changes were linked with immune system decline (CD4+ T cell counts; P < 0.001) and cognitive impairment ( P < 0.009), but not viral load. Frontal horn maps distinguished AIDS patients from controls better than occipital and temporal horn measures. T cell decline linked with callosal thinning in anterior regions connecting frontal areas with greatest cortical atrophy. Conclusion: These maps (1) reveal how brain changes in HIV/AIDS relate to immune decline and impaired cognition, and, after further validation and testing, (2) may offer possible neuroimaging markers for anti-viral drug trials, which gauge how well treatments oppose disease progression in the brain.

Skinning 3D meshes

A planar parameterization of 3D surfaces is useful for many applications. The applicability of the parameterization depends on how well it preserves the surface geometry (angles, distances, and areas). For most surface meshes there is no parameterization which preserves the geometry exactly. The distortion usually increases with the rise in surface complexity. For highly complicated surfaces the distortion can become so strong as to make the parameterization unusable for application’s purposes. A solution is to partition the surface or introduce cuts in a way which will reduce the distortion. This article presents a new method for cutting seams in 3D mesh surfaces. The addition of seams reduces the surface complexity and hence reduces the metric distortion produced by the parameterization. Seams often introduce additional constraints on the application for which the parameterization is used, hence their length should be minimal. The presented method minimizes the seam length while reducing the parameterization distortion to acceptable level.

Multiple material marching cubes algorithm

AbstractThe accurate reconstruction of three‐dimensional (3D) boundary surfaces from two‐dimensional (2D) medical images is a crucial procedure in most applications of computational biomedical engineering. This paper addresses an innovative system that efficiently reconstructs accurate, multiple‐material, 3D surface meshes from 2D medical images. It is based on an enhanced marching cubes algorithm, the multi‐material marching cubes algorithm (M3C), which extracts boundary surfaces between different materials within one sweep of the image stack in an integrated manner. The continuity and integrity of the surfaces are ensured with this robust algorithm. Surface adjustment algorithms were also revised to adapt to the multiple‐material nature of the system. Copyright © 2003 John Wiley &amp; Sons, Ltd.