35-Issue 7

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https://diglib.eg.org/handle/10.2312/2630929

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Adaptive Bas-relief Generation from 3D Object under Illumination
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Zhang, Yu-Wei; Zhang, Caiming; Wang, Wenping; Chen, Yanzhao; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
Bas-relief is designed to provide 3D perception for the viewers under illumination. For the problem of bas-relief generation from 3D object, most existing methods ignore the influence of illumination on bas-relief appearance. In this paper, we propose a novel method that adaptively generate bas-reliefs with respect to illumination conditions. Given a 3D object and its target appearance, our method finds an adaptive surface that preserves the appearance of the input. We validate our approach through a variety of applications. Experimental results indicate that the proposed approach is effective in producing bas-reliefs with desired appearance under illumination.
Automatic Modeling of Urban Facades from Raw LiDAR Point Data
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Wang, Jun; Xu, Yabin; Remil, Oussama; Xie, Xingyu; Ye, Nan; Wei, Mingqiang; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
Modeling of urban facades from raw LiDAR point data remains active due to its challenging nature. In this paper, we propose an automatic yet robust 3D modeling approach for urban facades with raw LiDAR point clouds. The key observation is that building facades often exhibit repetitions and regularities. We hereby formulate repetition detection as an energy optimization problem with a global energy function balancing geometric errors, regularity and complexity of facade structures. As a result, repetitive structures are extracted robustly even in the presence of noise and missing data. By registering repetitive structures, missing regions are completed and thus the associated point data of structures are well consolidated. Subsequently, we detect the potential design intents (i.e., geometric constraints) within structures and perform constrained fitting to obtain the precise structure models. Furthermore, we apply structure alignment optimization to enforce position regularities and employ repetitions to infer missing structures. We demonstrate how the quality of raw LiDAR data can be improved by exploiting data redundancy, and discovering high level structural information (regularity and symmetry). We evaluate our modeling method on a variety of raw LiDAR scans to verify its robustness and effectiveness.
Efficient Modeling of Entangled Details for Natural Scenes
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Guérin, Eric; Galin, Eric; Grosbellet, François; Peytavie, Adrien; Génevaux, Jean-David; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
Digital landscape realism often comes from the multitude of details that are hard to model such as fallen leaves, rock piles or entangled fallen branches. In this article, we present a method for augmenting natural scenes with a huge amount of details such as grass tufts, stones, leaves or twigs. Our approach takes advantage of the observation that those details can be approximated by replications of a few similar objects and therefore relies on mass-instancing. We propose an original structure, the Ghost Tile, that stores a huge number of overlapping candidate objects in a tile, along with a pre-computed collision graph. Details are created by traversing the scene with the Ghost Tile and generating instances according to user-defined density fields that allow to sculpt layers and piles of entangled objects while providing control over their density and distribution.
Efficient Volumetric PolyCube-Map Construction
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Fu, Xiao-Ming; Bai, Chong-Yang; Liu, Yang; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
PolyCubes provide compact representations for closed complex shapes and are essential to many computer graphics applications. Existing automatic PolyCube construction methods usually suffer from poor quality or time-consuming computation. In this paper, we provide a highly efficient method to compute volumetric PolyCube-maps. Given an input tetrahedral mesh, we utilize two novel normal-driven volumetric deformation schemes and a polycube-allowable mesh segmentation to drive the input to a volumetric PolyCube structure. Our method can robustly generate foldover-free and low-distortion PolyCube-maps in practice, and provide a flexible control on the number of corners of Polycubes. Compared with state-of-the-art methods, our method is at least one order of magnitude faster and has better mapping qualities. We demonstrate the efficiency and efficacy of our method in PolyCube construction and all-hexahedral meshing on various complex models.
An Eulerian Approach for Constructing a Map Between Surfaces With Different Topologies
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Park, Hangil; Cho, Youngjin; Bang, Seungbae; Lee, Sung-Hee; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
3D objects of the same kind often have different topologies, and finding correspondence between them is important for operations such as morphing, attribute transfer, and shape matching. This paper presents a novel method to find the surface correspondence between topologically different surfaces. The method is characterized by deforming the source polygonal mesh to match the target mesh by using the intermediate implicit surfaces, and by performing a topological surgery at the appropriate locations on the mesh. In particular, we propose a mathematically well-defined way to detect the topology change of surface by finding the non-degenerate saddle points of the velocity fields that tracks implicit surfaces. We show the effectiveness and possible applications of the proposed method through several experiments.
Harmonic Functions for Rotational Symmetry Vector Fields
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Shen, Zhongwei; Fang, Xianzhong; Liu, Xinguo; Bao, Hujun; Huang, Jin; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
Representing rotational symmetry vector as a set of vectors is not suitable for design due to lacking of a consistent ordering for measurement. In this paper we introduce a spectral method to find rotation invariant harmonic functions for symmetry vector field design. This method is developed for 3D vector fields, but it is applicable in 2D. Given the finite symmetry group G of a symmetry vector field v(x) on a 3D domain W, we formulate the harmonic function h(s) as a stationary point of group G. Using the real spherical harmonic (SH) bases, we showed the coefficients of the harmonic functions are an eigenvector of the SH rotation matrices corresponding to group G. Instead of solving eigen problems to obtain the eigenvector, we developed a forward constructive method based on orthogonal group theory. The harmonic function found by our method is not only invariant under G, but also expressive and can distinguish different rotations with respect to G. At last, we demonstrate some vector field design results with tetrahedron-symmetry, cube-symmetry and dodecahedron-symmetry groups.
An Interactive Design System of Free-Formed Bamboo-Copters
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Nakamura, Morihiro; Koyama, Yuki; Sakamoto, Daisuke; Igarashi, Takeo; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
We present an interactive design system for designing free-formed bamboo-copters, where novices can easily design freeformed, even asymmetric bamboo-copters that successfully fly. The designed bamboo-copters can be fabricated using digital fabrication equipment, such as a laser cutter. Our system provides two useful functions for facilitating this design activity. First, it visualizes a simulated flight trajectory of the current bamboo-copter design, which is updated in real time during the user's editing. Second, it provides an optimization function that automatically tweaks the current bamboo-copter design such that the spin quality-how stably it spins-and the flight quality-how high and long it flies-are enhanced. To enable these functions, we present non-trivial extensions over existing techniques for designing free-formed model airplanes [UKSI14], including a wing discretization method tailored to free-formed bamboo-copters and an optimization scheme for achieving stable bamboocopters considering both spin and flight qualities.
Piecewise-planar Reconstruction of Multi-room Interiors with Arbitrary Wall Arrangements
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Mura, Claudio; Mattausch, Oliver; Pajarola, Renato; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
Reconstructing the as-built architectural shape of building interiors has emerged in recent years as an important and challenging research problem. An effective approach must be able to faithfully capture the architectural structures and separate permanent components from clutter (e.g. furniture), while at the same time dealing with defects in the input data. For many applications, higher-level information on the environment is also required, in particular the shape of individual rooms. To solve this ill-posed problem, state-of-the-art methods assume constrained input environments with a 2.5D or, more restrictively, a Manhattan-world structure, which significantly restricts their applicability in real-world settings. We present a novel pipeline that allows to reconstruct general 3D interior architectures, significantly increasing the range of real-world architectures that can be reconstructed and labeled by any interior reconstruction method to date. Our method finds candidate permanent components by reasoning on a graph-based scene representation, then uses them to build a 3D linear cell complex that is partitioned into separate rooms through a multi-label energy minimization formulation. We demonstrate the effectiveness of our method by applying it to a variety of real-world and synthetic datasets and by comparing it to more specialized state-of-the-art approaches.
Retargeting 3D Objects and Scenes with a General Framework
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Huang, Chun-Kai; Chen, Yi-Ling; Shen, I-Chao; Chen, Bing-Yu; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
In this paper, we introduce an interactive method suitable for retargeting both 3D objects and scenes. Initially, the input object or scene is decomposed into a collection of constituent components enclosed by corresponding control bounding volumes which capture the intra-structures of the object or semantic grouping of objects in the 3D scene. The overall retargeting is accomplished through a constrained optimization by manipulating the control bounding volumes. Without inferring the intricate dependencies between the components, we define a minimal set of constraints that maintain the spatial arrangement and connectivity between the components to regularize the valid retargeting results. The default retargeting behavior can then be easily altered by additional semantic constraints imposed by users. This strategy makes the proposed method highly flexible to process a wide variety of 3D objects and scenes under an unified framework. In addition, the proposed method achieved more general structure-preserving pattern synthesis in both object and scene levels. We demonstrate the effectiveness of our method by applying it to several complicated 3D objects and scenes.
Skeleton-driven Adaptive Hexahedral Meshing of Tubular Shapes
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Livesu, Marco; Muntoni, Alessandro; Puppo, Enrico; Scateni, Riccardo; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
We propose a novel method for the automatic generation of structured hexahedral meshes of articulated 3D shapes. We recast the complex problem of generating the connectivity of a hexahedral mesh of a general shape into the simpler problem of generating the connectivity of a tubular structure derived from its curve-skeleton. We also provide volumetric subdivision schemes to nicely adapt the topology of the mesh to the local thickness of tubes, while regularizing per-element size. Our method is fast, one-click, easy to reproduce, and it generates structured meshes that better align to the branching structure of the input shape if compared to previous methods for hexa mesh generation.
Spatial Matching of Animated Meshes
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Seo, Hyewon; Cordier, Frederic; Eitan Grinspun and Bernd Bickel and Yoshinori Dobashi
This paper presents a new technique which makes use of deformation and motion properties between animated meshes for finding their spatial correspondences. Given a pair of animated meshes exhibiting a semantically similar motion, we compute a sparse set of feature points on each mesh and compute spatial correspondences among them so that points with similar motion behavior are put in correspondence. At the core of our technique is our new, dynamic feature descriptor named AnimHOG, which encodes local deformation characteristics. AnimHOG is ob-tained by computing the gradient of a scalar field inside the spatiotemporal neighborhood of a point of interest, where the scalar values are obtained from the deformation characteristic associated with each vertex and at each frame. The final matching has been formulated as a discreet optimization problem that finds the matching of each feature point on the source mesh so that the descriptor similarity between the corresponding feature pairs as well as compatibility and consistency as measured across the pairs of correspondences are maximized. Consequently, reliable correspondences can be found even among the meshes of very different shape, as long as their motions are similar. We demonstrate the performance of our technique by showing the good quality of matching results we obtained on a number of animated mesh pairs.

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Browsing 35-Issue 7 by Subject "Computational Geometry and Object Modeling"

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