EG2016

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https://diglib.eg.org/handle/10.2312/15062

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Sketch-based Modeling
(The Eurographics Association, 2016) Cordier, Frederic; Singh, Karan; Etem, Even; Cani, Marie-Paule; Gingold, Yotam; Augusto Sousa and Kadi Bouatouch
Sketching is one of the most natural ways to exchange ideas. It has been used by human beings since prehistory. Research has shown that human beings have an inherent ability to understand sketches. This is why sketch-based interfaces for 3D modeling are so appealing; creating and animating 3D shapes could become as simple as drawing with a tablet and a digital pen. The purpose of this tutorial is to explore the most important aspects of sketch-based modeling, from the preprocessing of sketch strokes to the problem of 3D reconstruction. We will first explain some aspects of how humans interpret sketches. The second part of the tutorial will be dedicated to the problem of filtering and processing strokes. Other parts of the tutorial will focus on the sketch-based modeling of curves and surfaces using multi-view and single-view sketches. Sketch-based modeling using prior-knowledge will be also discussed; this class of methods is particularly well adapted to the 3D reconstruction of complex shapes. The last part of the tutorial addresses sketch-based interfaces for editing 3D shapes.
EUROGRAPHICS 2016: Posters Frontmatter
(Eurographics Association, 2016) Luis Gonzaga Magalhães; Rafał Mantiuk;
Generalized As-Similar-As-Possible Warping with Applications in Digital Photography
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Chen, Renjie; Gotsman, Craig; Joaquim Jorge and Ming Lin
Discrete conformal mappings of planar triangle meshes, also known as the As-Similar-As-Possible (ASAP) mapping, involve the minimization of a quadratic energy function, thus are very easy to generate and are popular in image warping scenarios. We generalize this classical mapping to the case of quad meshes, taking into account the mapping of the interior of the quad, and analyze in detail the most common case - the unit grid mesh. We show that the generalization, when combined with barycentric coordinate mappings between the source and target polygons, spawns an entire family of new mappings governed by quadratic energy functions, which allow to control quite precisely various effects of the mapping. This approach is quite general and applies also to arbitrary planar polygon meshes. As an application of generalized ASAP mappings of the unit grid mesh, we demonstrate how they can be used to warp digital photographs to achieve a variety of effects. One such effect is modifying the perspective of the camera that took a given photograph (without moving the camera). A related, but more challenging, effect is re-photography - warping a contemporary photograph in order to reproduce the camera view present in a vintage photograph of the same scene - taken many years before with a different camera from a different viewpoint. We apply the generalized ASAP mapping to these images, discretized to a unit grid. Using a quad mesh (as opposed to a triangle mesh) permits biasing towards affine maps of the unit squares. This allows the introduction of an As-Affine-As-Possible (AAAP) mapping for a good approximation of the homographies present in these warps, achieving quite accurate results. We demonstrate the advantages of the AAAP mapping on a variety of synthetic and real-world examples.
No-infill 3D Printing
(The Eurographics Association, 2016) Wei, Xiaoran; Geng, Guohua; Zhang, Yuhe; Luis Gonzaga Magalhaes and Rafal Mantiuk
This paper introduces a partition method for printing hollow objects without infill via Fused Deposition Modeling (FDM), which is one of the most widely used 3D-printing technology. We linked the partition problem to the exact cover problem (ECP). Then the hollow objects can be printed without any infill. The experimental results show that our solution can be applied to a variety of models, closed-hollowed or semi-closed, with or without holes, as evidenced by experiments and performance evaluation on our proposed algorithm.
Terracotta Reassembly from Fragments Based on Surface Ornamentation Adjacency Constraints
(The Eurographics Association, 2016) Zhang, Yuhe; Geng, Guohua; Wei, Xiaoran; Zhang, Shunli; Luis Gonzaga Magalhaes and Rafal Mantiuk
This paper introduces a method that enables the reassembly of fragments with incompleteness in fracture surfaces and break-curves. The incompleteness of the fracture surfaces and break-curves, both contribute to the failure of all previous geometry-driven techniques for reassembly of 3D objects. The proposed method is preferable because it depends on the surface ornamentation-the structured feature lines, which are often complete and can provide enough surface adjacency constraints. Finally, we demonstrate the benefits of our method with the favorable results for real-world point clouds of Terracotta.
Robust Transmission of Motion Capture Data using Interleaved LDPC and Inverse Kinematics
(The Eurographics Association, 2016) Furtado, Antonio Carlos; Cheng, Irene; Dufaux, Frederic; Basu, Anup; T. Bashford-Rogers and L. P. Santos
Recent advances in smart-sensor technology have improved precision in Motion Capture (MoCap) data for realistic animation. However, precision also imposes challenges on bandwidth. While research efforts have focussed on MoCap compression in recent years, little attention has been given to lossy transmission taking advantage of the human perceptual threshold, which allows many online applications, e.g., interactive games, on-demand broadcast, movies and tutoring using dynamic motion sequences. Given the growing applications on mobile devices and wireless networks, associated with insufficient bandwidth, unreliable connection and potential interference or shadowing, data loss is inevitable. We introduce a new Representation for MoCap data, integrating Interleaved Low-Density Parity-Check (I-LDPC), with Keyframe-based Interpolation and Inverse Kinematics, to better address the problem of MoCap data loss during transmission. We believe this is the first study to address robust transmission of MoCap data considering loss. Experimental results assessed using mean opinion scores demonstrate that our approach achieves substantial improvement over alternative transmission methods.
Laplacian Spectral Kernels and Distances for Geometry Processing and Shape Analysis
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Patané, Giuseppe; Joaquim Madeira and Gustavo Patow
In geometry processing and shape analysis, several applications have been addressed through the properties of the spectral kernels and distances, such as commute-time, biharmonic, diffusion, and wave distances. Our survey is intended to provide a background on the properties, discretization, computation, and main applications of the Laplace-Beltrami operator, the associated differential equations (e.g., harmonic equation, Laplacian eigenproblem, diffusion and wave equations), Laplacian spectral kernels and distances (e.g., commute-time, biharmonic, wave, diffusion distances). While previous work has been focused mainly on specific applications of the aforementioned topics on surface meshes, we propose a general approach that allows us to review Laplacian kernels and distances on surfaces and volumes, and for any choice of the Laplacian weights. All the reviewed numerical schemes for the computation of the Laplacian spectral kernels and distances are discussed in terms of robustness, approximation accuracy, and computational cost, thus supporting the reader in the selection of the most appropriate method with respect to shape representation, computational resources, and target application.
Data-guided Model Predictive Control Based on Smoothed Contact Dynamics
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Han, Daseong; Eom, Haegwang; Noh, Junyong; Shin, Joseph S. (formerly Sung Yong); Joaquim Jorge and Ming Lin
In this paper, we propose an efficient data-guided method based on Model Predictive Control (MPC) to synthesize a full-body motion. Guided by a reference motion, our method repeatedly plans the full-body motion to produce an optimal control policy for predictive control while sliding the fixed-span window along the time axis. Based on this policy, the method computes the joint torques of a character at every time step. Together with contact forces and external perturbations if there are any, the joint torques are used to update the state of the character. Without including the contact forces in the control vector, our formulation of the trajectory optimization problem enables automatic adjustment of contact timings and positions for balancing in response to environmental changes and external perturbations. For efficiency, we adopt derivative-based trajectory optimization on top of state-of-the-art smoothed contact dynamics. Use of derivatives enables our method to run much faster than the existing sampling-based methods. In order to further accelerate the performance of MPC, we propose efficient numerical differentiation of the system dynamics of a full-body character based on two schemes: data reuse and data interpolation. The former scheme exploits data dependency to reuse physical quantities of the system dynamics at near-by time points. The latter scheme allows the use of derivatives at sparse sample points to interpolate those at other time points in the window. We further accelerate evaluation of the system dynamics by exploiting the sparsity of physical quantities such as Jacobian matrix resulting from the tree-like structure of the articulated body. Through experiments, we show that the proposed method efficiently can synthesize realistic motions such as locomotion, dancing, gymnastic motions, and martial arts at interactive rates using moderate computing resources.
Multi-Resolution Meshes for Feature-Aware Hardware Tessellation
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Lambert, Thibaud; Bénard, Pierre; Guennebaud, Gaël; Joaquim Jorge and Ming Lin
Hardware tessellation is de facto the preferred mechanism to adaptively control mesh resolution with maximal performances. However, owing to its fixed and uniform pattern, leveraging tessellation for feature-aware LOD rendering remains a challenging problem. We relax this fundamental constraint by introducing a new spatial and temporal blending mechanism of tessellation levels, which is built on top of a novel hierarchical representation of multi-resolution meshes. This mechanism allows to finely control topological changes so that vertices can be removed or added at the most appropriate location to preserve geometric features in a continuous and artifact-free manner. We then show how to extend edge-collapse based decimation methods to build feature-aware multi-resolution meshes that match the tessellation patterns. Our approach is fully compatible with current hardware tessellators and only adds a small overhead on memory consumption and tessellation cost.
3D Skeletons: A State-of-the-Art Report
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Tagliasacchi, Andrea; Delame, Thomas; Spagnuolo, Michela; Amenta, Nina; Telea, Alexandru; Joaquim Madeira and Gustavo Patow
Given a shape, a skeleton is a thin centered structure which jointly describes the topology and the geometry of the shape. Skeletons provide an alternative to classical boundary or volumetric representations, which is especially effective for applications where one needs to reason about, and manipulate, the structure of a shape. These skeleton properties make them powerful tools for many types of shape analysis and processing tasks. For a given shape, several skeleton types can be defined, each having its own properties, advantages, and drawbacks. Similarly, a large number of methods exist to compute a given skeleton type, each having its own requirements, advantages, and limitations. While using skeletons for two-dimensional (2D) shapes is a relatively well covered area, developments in the skeletonization of three-dimensional (3D) shapes make these tasks challenging for both researchers and practitioners. This survey presents an overview of 3D shape skeletonization. We start by presenting the definition and properties of various types of 3D skeletons. We propose a taxonomy of 3D skeletons which allows us to further analyze and compare them with respect to their properties. We next overview methods and techniques used to compute all described 3D skeleton types, and discuss their assumptions, advantages, and limitations. Finally, we describe several applications of 3D skeletons, which illustrate their added value for different shape analysis and processing tasks.
A Practical Method for High-Resolution Embedded Liquid Surfaces
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Goldade, Ryan; Batty, Christopher; Wojtan, Chris; Joaquim Jorge and Ming Lin
Combining high-resolution level set surface tracking with lower resolution physics is an inexpensive method for achieving highly detailed liquid animations. Unfortunately, the inherent resolution mismatch introduces several types of disturbing visual artifacts. We identify the primary sources of these artifacts and present simple, efficient, and practical solutions to address them. First, we propose an unconditionally stable filtering method that selectively removes sub-grid surface artifacts not seen by the fluid physics, while preserving fine detail in dynamic splashing regions. It provides comparable results to recent error-correction techniques at lower cost, without substepping, and with better scaling behavior. Second, we show how a modified narrow-band scheme can ensure accurate free surface boundary conditions in the presence of large resolution mismatches. Our scheme preserves the efficiency of the narrow-band methodology, while eliminating objectionable stairstep artifacts observed in prior work. Third, we demonstrate that the use of linear interpolation of velocity during advection of the high-resolution level set surface is responsible for visible grid-aligned kinks; we therefore advocate higher-order velocity interpolation, and show that it dramatically reduces this artifact. While these three contributions are orthogonal, our results demonstrate that taken together they efficiently address the dominant sources of visual artifacts arising with high-resolution embedded liquid surfaces; the proposed approach offers improved visual quality, a straightforward implementation, and substantially greater scalability than competing methods.
EUROGRAPHICS 2016: Short Papers Frontmatter
(Eurographics Association, 2016) Luis Paulo Santos; Tom Bashford-Rogers;
A 3D Morphable Model of the Eye Region
(The Eurographics Association, 2016) Wood, Erroll; Baltrušaitis, Tadas; Morency, Louis-Philippe; Robinson, Peter; Bulling, Andreas; Luis Gonzaga Magalhaes and Rafal Mantiuk
We present the first 3D morphable model that includes the eyes, enabling gaze estimation and gaze re-targetting from a single image. Morphable face models are a powerful tool and are used for a range of tasks including avatar animation and facial expression transfer. However, previous work has avoided the eyes, even though they play an important role in human communication. We built a new morphable model of the facial eye-region from high-quality head scan data, and combined this with a parametric eyeball model constructed from anatomical measurements and iris photos. We fit our models to an input RGB image, solving for shape, texture, pose, and scene illumination simultaneously. This provides us with an estimate of where a person is looking in a 3D scene without per-user calibration - a still unsolved problem in computer vision. It also allows us to re-render a person's eyes with different parameters, thus redirecting their perceived attention.
Anisotropic Diffusion Descriptors
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Boscaini, Davide; Masci, Jonathan; Rodolà, Emanuele; Bronstein, Michael M.; Cremers, Daniel; Joaquim Jorge and Ming Lin
Spectral methods have recently gained popularity in many domains of computer graphics and geometry processing, especially shape processing, computation of shape descriptors, distances, and correspondence. Spectral geometric structures are intrinsic and thus invariant to isometric deformations, are efficiently computed, and can be constructed on shapes in different representations. A notable drawback of these constructions, however, is that they are isotropic, i.e., insensitive to direction. In this paper, we show how to construct direction-sensitive spectral feature descriptors using anisotropic diffusion on meshes and point clouds. The core of our construction are directed local kernels acting similarly to steerable filters, which are learned in a task-specific manner. Remarkably, while being intrinsic, our descriptors allow to disambiguate reflection symmetries. We show the application of anisotropic descriptors for problems of shape correspondence on meshes and point clouds, achieving results significantly better than state-of-the-art methods.
Space-Time Co-Segmentation of Articulated Point Cloud Sequences
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Yuan, Qing; Li, Guiqing; Xu, Kai; Chen, Xudong; Huang, Hui; Joaquim Jorge and Ming Lin
Consistent segmentation is to the center of many applications based on dynamic geometric data. Directly segmenting a raw 3D point cloud sequence is a challenging task due to the low data quality and large inter-frame variation across the whole sequence. We propose a local-to-global approach to co-segment point cloud sequences of articulated objects into near-rigid moving parts. Our method starts from a per-frame point clustering, derived from a robust voting-based trajectory analysis. The local segments are then progressively propagated to the neighboring frames with a cut propagation operation, and further merged through all frames using a novel space-time segment grouping technqiue, leading to a globally consistent and compact segmentation of the entire articulated point cloud sequence. Such progressive propagating and merging, in both space and time dimensions, makes our co-segmentation algorithm especially robust in handling noise, occlusions and pose/view variations that are usually associated with raw scan data.
Skyglow: Towards a Night-time Illumination Model for Urban Environments
(The Eurographics Association, 2016) Minor, Tom; Poncelet, Robert R.; Anderson, Eike Falk; Luis Gonzaga Magalhaes and Rafal Mantiuk
For night-time scenes in computer graphics there exist few consistent models or implementations for sky illumination, and those that do exist lack the feature of light pollution from artificial light sources. We present initial results for a physically-based night sky model including this ''skyglow''. Our model extends the existing models with the aforementioned ''skyglow'' from artificial light sources, using a technique derived from equations developed in the field of astronomy and adapted for a computer graphics context. Our current model has been implemented for Pixar's RenderMan renderer and also been trialled with ShaderToy.
Garment Transfer for Quadruped Characters
(The Eurographics Association, 2016) Narita, Fumiya; Saito, Shunsuke; Kato, Takuya; Fukusato, Tsukasa; Morishima, Shigeo; T. Bashford-Rogers and L. P. Santos
Modeling clothing to characters is one of the most time-consuming tasks for artists in 3DCG animation production. Transferring existing clothing models is a simple and powerful solution to reduce labor. In this paper, we propose a method to generate a clothing model for various characters from a single template model. Our framework consists of three steps: scale measurement, clothing transformation, and texture preservation. By introducing a novel measurement of the scale deviation between two characters with different shapes and poses, our framework achieves pose-independent transfer of clothing even for quadrupeds (e.g., from human to horse). In addition to a plausible clothing transformation method based on the scale measurement, our method minimizes texture distortion resulting from large deformation. We demonstrate that our system is robust for a wide range of body shapes and poses, which is challenging for current state-of-the-art methods.
BRDF Representation and Acquisition
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Guarnera, Dar'ya; Guarnera, Giuseppe Claudio; Ghosh, Abhijeet; Denk, Cornelia; Glencross, Mashhuda; Joaquim Madeira and Gustavo Patow
Photorealistic rendering of real world environments is important in a range of different areas; including Visual Special effects, Interior/Exterior Modelling, Architectural Modelling, Cultural Heritage, Computer Games and Automotive Design. Currently, rendering systems are able to produce photorealistic simulations of the appearance of many real-world materials. In the real world, viewer perception of objects depends on the lighting and object/material/surface characteristics, the way a surface interacts with the light and on how the light is reflected, scattered, absorbed by the surface and the impact these characteristics have on material appearance. In order to re-produce this, it is necessary to understand how materials interact with light. Thus the representation and acquisition of material models has become such an active research area. This survey of the state-of-the-art of BRDF Representation and Acquisition presents an overview of BRDF (Bidirectional Reflectance Distribution Function) models used to represent surface/material reflection characteristics, and describes current acquisition methods for the capture and rendering of photorealistic materials.
SAH Guided Spatial Split Partitioning for Fast BVH Construction
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Ganestam, Per; Doggett, Michael; Joaquim Jorge and Ming Lin
We present a new SAH guided approach to subdividing triangles as the scene is coarsely partitioned into smaller sets of spatially coherent triangles. Our triangle split approach is integrated into the partitioning stage of a fast BVH construction algorithm, but may as well be used as a stand alone pre-split pass. Our algorithm significantly reduces the number of split triangles compared to previous methods, while at the same time improving ray tracing performance compared to competing fast BVH construction techniques. We compare performance on Intel's Embree ray tracer and show that BVH construction with our splitting algorithm is always faster than Embree's pre-split construction algorithm. We also show that our algorithm builds significantly improved quality trees that deliver higher ray tracing performance. Our algorithm is implemented into Embree's open source ray tracing framework, and the source code will be released late 2015.
Subjective and Objective Evaluation of Multi-exposure High Dynamic Range Image Deghosting Methods
(The Eurographics Association, 2016) Karaduzovic-Hadziabdic, Kanita; Telalovic, Jasminka Hasic; Mantiuk, Rafal; T. Bashford-Rogers and L. P. Santos
To avoid motion artefacts when merging multiple exposures into an HDR image, a number of deghosting algorithms have been proposed. These algorithms, however, do not work equally well on all types of scenes, and some may even introduce additional artefacts. Even though subjective methods of evaluation provide reliable means of testing, they need to be repeated for each new proposed method or even its slight modification and are cumbersome to perform. In this work, we evaluate several computational approaches of quantitative evaluation of multi-exposure HDR deghosting algorithms and demonstrate their results on five state-of-the-art algorithms.The quality of HDR images produced by deghosting methods is measured in a subjective experiment, and then evaluated using five objective metrics. The most reliable metrics is then selected by testing correlation between subjective and objective metric scores.

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