EG2015

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https://diglib.eg.org/handle/10.2312/12086

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Target Temperature Driven Dynamic Flame Animation
(The Eurographics Association, 2015) Cui, Qiaodong; Wu, Zhaohui; Xing, Chang; Zhou, Zhong; Wu, Wei; B. Bickel and T. Ritschel
Fire/flame plays an important role in virtual environment. Controlling the flame behavior in an intuitive yet precise manner remains a challenging open problem. In this paper, a target temperature driven simulation method is proposed to control flame animation. The diverse descriptions of target flame are unified by temperature field. An adaptive control force is presented to control the degree of target-driven changing over the temperature field. A bidirectional iterative method is proposed to subdivide the final goal into a plurality of intermediate targets. We take geometric model, image, and temperature field as target flames to test our method. Experimental results show that this method allows complex flame animations to be controllably generated with very little additional cost compared to ordinary flow simulations.
Statics Aware Grid Shells
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Pietroni, Nico; Tonelli, Davide; Puppo, Enrico; Froli, Maurizio; Scopigno, Roberto; Cignoni, Paolo; Olga Sorkine-Hornung and Michael Wimmer
We introduce a framework for the generation of polygonal grid-shell architectural structures, whose topology is designed in order to excel in static performances. We start from the analysis of stress on the input surface and we use the resulting tensor field to induce an anisotropic non-Euclidean metric over it. This metric is derived by studying the relation between the stress tensor over a continuous shell and the optimal shape of polygons in a corresponding grid-shell. Polygonal meshes with uniform density and isotropic cells under this metric exhibit variable density and anisotropy in Euclidean space, thus achieving a better distribution of the strain energy over their elements. Meshes are further optimized taking into account symmetry and regularity of cells to improve aesthetics. We experiment with quad meshes and hex-dominant meshes, demonstrating that our grid-shells achieve better static performances than state-of-the-art grid-shells.
3D Fabrication of 2D Mechanisms
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Hergel, Jean; Lefebvre, Sylvain; Olga Sorkine-Hornung and Michael Wimmer
The success of physics sandbox applications and physics-based puzzle games is a strong indication that casual users and hobbyists enjoy designing mechanisms, for educational or entertainment purposes. In these applications, a variety of mechanisms are designed by assembling two-dimensional shapes, creating gears, cranks, cams, and racks. The experience is made enjoyable by the fact that the user does not need to worry about the intricate geometric details that would be necessary to produce a real mechanism. In this paper, we propose to start from such casual designs of mechanisms and turn them into a 3D model that can be printed onto widely available, inexpensive filament based 3D printers. Our intent is to empower the users of such tools with the ability to physically realize their mechanisms and see them operate in the real world. To achieve this goal we tackle several challenges. The input 2D mechanism allows for some parts to overlap during simulation. These overlapping parts have to be resolved into non-intersecting 3D parts in the real mechanism. We introduce a novel scheme based on the idea of including moving parts into one another whenever possible. This reduces bending stresses on axles compared to previous methods. Our approach supports sliding parts and arbitrarily shaped mechanical parts in the 2D input. The exact 3D shape of the parts is inferred from the 2D input and the simulation of the mechanism, using boolean operations between shapes. The input mechanism is often simply attached to the background. We automatically synthesize a chassis by formulating a topology optimization problem, taking into account the stresses exerted by the mechanism on the chassis through time.
Panoramic Video from Unstructured Camera Arrays
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Perazzi, Federico; Sorkine-Hornung, Alexander; Zimmer, Henning; Kaufmann, Peter; Wang, Oliver; Watson, Scott; Gross, Markus; Olga Sorkine-Hornung and Michael Wimmer
We describe an algorithm for generating panoramic video from unstructured camera arrays. Artifact-free panorama stitching is impeded by parallax between input views. Common strategies such as multi-level blending or minimum energy seams produce seamless results on quasi-static input. However, on video input these approaches introduce noticeable visual artifacts due to lack of global temporal and spatial coherence. In this paper we extend the basic concept of local warping for parallax removal. Firstly, we introduce an error measure with increased sensitivity to stitching artifacts in regions with pronounced structure. Using this measure, our method efficiently finds an optimal ordering of pair-wise warps for robust stitching with minimal parallax artifacts. Weighted extrapolation of warps in non-overlap regions ensures temporal stability, while at the same time avoiding visual discontinuities around transitions between views. Remaining global deformation introduced by the warps is spread over the entire panorama domain using constrained relaxation, while staying as close as possible to the original input views. In combination, these contributions form the first system for spatiotemporally stable panoramic video stitching from unstructured camera array input.
Distilled Collections from Textual Image Queries
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Averbuch-Elor, Hadar; Wan, Yunhai; Qian, Yiming; Gong, Minglun; Kopf, Johannes; Zhang, Hao; Cohen-Or, Daniel; Olga Sorkine-Hornung and Michael Wimmer
We present a distillation algorithm which operates on a large, unstructured, and noisy collection of internet images returned from an online object query. We introduce the notion of a distilled set, which is a clean, coherent, and structured subset of inlier images. In addition, the object of interest is properly segmented out throughout the distilled set. Our approach is unsupervised, built on a novel clustering scheme, and solves the distillation and object segmentation problems simultaneously. In essence, instead of distilling the collection of images, we distill a collection of loosely cutout foreground ''shapes'', which may or may not contain the queried object. Our key observation, which motivated our clustering scheme, is that outlier shapes are expected to be random in nature, whereas, inlier shapes, which do tightly enclose the object of interest, tend to be well supported by similar shapes captured in similar views. We analyze the commonalities among candidate foreground segments, without aiming to analyze their semantics, but simply by clustering similar shapes and considering only the most significant clusters representing non-trivial shapes. We show that when tuned conservatively, our distillation algorithm is able to extract a near perfect subset of true inliers. Furthermore, we show that our technique scales well in the sense that the precision rate remains high, as the collection grows. We demonstrate the utility of our distillation results with a number of interesting graphics applications.
Adaptive LightSlice for Virtual Ray Lights
(The Eurographics Association, 2015) Frederickx, Roald; Bartels, Pieterjan; Dutré, Philip; B. Bickel and T. Ritschel
We speed up the rendering of participating media with Virtual Ray Lights (VRLs) by clustering them in a preprocessing step. A subset of representative VRLs is then sampled from the clustering, which is used for the final rendering. By performing a full variance analysis, we can explicitly estimate the convergence rate of the rendering process and automatically find the locally ideal number of clusters to maximize efficiency. Overall, we report speed-up factors ranging from 13 to 16 compared to unclustered rendering.
SmartAnnotator: An Interactive Tool for Annotating Indoor RGBD Images
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Wong, Yu-Shiang; Chu, Hung-Kuo; Mitra, Niloy J.; Olga Sorkine-Hornung and Michael Wimmer
RGBD images with high quality annotations, both in the form of geometric (i.e., segmentation) and structural (i.e., how do the segments mutually relate in 3D) information, provide valuable priors for a diverse range of applications in scene understanding and image manipulation. While it is now simple to acquire RGBD images, annotating them, automatically or manually, remains challenging. We present SMARTANNOTATOR, an interactive system to facilitate annotating raw RGBD images. The system performs the tedious tasks of grouping pixels, creating potential abstracted cuboids, inferring object interactions in 3D, and generates an ordered list of hypotheses. The user simply has to flip through the suggestions for segment labels, finalize a selection, and the system updates the remaining hypotheses. As annotations are finalized, the process becomes simpler with fewer ambiguities to resolve. Moreover, as more scenes are annotated, the system makes better suggestions based on the structural and geometric priors learned from previous annotation sessions. We test the system on a large number of indoor scenes across different users and experimental settings, validate the results on existing benchmark datasets, and report significant improvements over low-level annotation alternatives. (Code and benchmark datasets are publicly available on the project page.)
PHENOM: Interest Points on Photometric Normal Maps
(The Eurographics Association, 2015) Sabzevari, Reza; Alak, Eren; Scaramuzza, Davide; B. Solenthaler and E. Puppo
This paper introduces a novel method for extracting features and matching points on images of texture-less surfaces. Feature points are extracted from surface normal maps recovered by Photometric Stereo. Such sparse matching will help to register high detail 3D surfaces reconstructed from multiple view images. Moreover, the geometric constraints imposed by multiple views can be utilized to correct the geometric ambiguity in photometric reconstruction. Experiments show the performance of proposed interest points in matching texture-less objects. Comparison against texture-based interest points shows that the proposed features based on normal maps perform effectively.
Quadratic Encoding for Hand Pose Reconstruction from Multi-Touch Input
(The Eurographics Association, 2015) Chung, Se-Joon; Kim, Junggon; Han, Shangchen; Pollard, Nancy S.; B. Bickel and T. Ritschel
One of the most compelling challenges in virtual reality today is to allow users to carry out virtual manipulation tasks using their hands. Multi-touch devices are an interesting interface for this task, as they are widely available, they provide users with some haptic sensation of their motions, and they give very precise locations of the fingertips. We introduce a quadratic encoding technique to provide plausible and smooth hand reconstructions from multi-touch input at real-time rates suitable for virtual reality applications. Another nice feature of our datadriven approach is that it does not require explicit identification or registration of fingers. We show that quadratic encoding outperforms linear encoding, cubic encoding, and a PCA based inverse kinematics approach, and is well suited for performing real-time virtual manipulation using a multi-touch device.
Light Chisel: 6DOF Pen Tracking
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Bubník, Vojtech; Havran, Vlastimil; Olga Sorkine-Hornung and Michael Wimmer
We present a novel interaction device tracked in 6 degrees of freedom by two commodity cameras. The inexpensive Light Chisel is statically illuminated with two LEDs, and uses no additional sensor (e.g. inertial or magnetic) or means of communication or synchronization. Its form factor is well suited for a screwdriver or chisel grip, allowing the Light Chisel to be rolled between the fingers. The position and orientation of the tool is tracked absolutely, making the Light Chisel suited for complex interaction, e.g. geometric modeling in augmented reality. The Light Chisel is physically small, limiting the physical and optical collisions with the real world. The orientation of the tool is tracked in a wide range of angles: pitch and yaw 90 , roll 180 . We evaluated our system against the OptiTrack optical tracking system. Our system achieved mean differences from OptiTrack reference of 2:07mm in position, 1:06 in yaw and pitch, and 5:26 in roll using a pair of VGA cameras. We demonstrate usefulness of our Light Chisel in four applications: character animation, modeling by swirls, volumetric modeling, and docking of CAD models.
A Biophysically-Based Model of the Optical Properties of Skin Aging
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Iglesias-Guitian, Jose A.; Aliaga, Carlos; Jarabo, Adrian; Gutierrez, Diego; Olga Sorkine-Hornung and Michael Wimmer
This paper presents a time-varying, multi-layered biophysically-based model of the optical properties of human skin, suitable for simulating appearance changes due to aging. We have identified the key aspects that cause such changes, both in terms of the structure of skin and its chromophore concentrations, and rely on the extensive medical and optical tissue literature for accurate data. Our model can be expressed in terms of biophysical parameters, optical parameters commonly used in graphics and rendering (such as spectral absorption and scattering coefficients), or more intuitively with higher-level parameters such as age, gender, skin care or skin type. It can be used with any rendering algorithm that uses diffusion profiles, and it allows to automatically simulate different types of skin at different stages of aging, avoiding the need for artistic input or costly capture processes. While the presented skin model is inspired on tissue optics studies, we also provided a simplified version valid for non-diagnostic applications.
Template Assembly for Detailed Urban Reconstruction
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Nan, Liangliang; Jiang, Caigui; Ghanem, Bernard; Wonka, Peter; Olga Sorkine-Hornung and Michael Wimmer
We propose a new framework to reconstruct building details by automatically assembling 3D templates on coarse textured building models. In a preprocessing step, we generate an initial coarse model to approximate a point cloud computed using Structure from Motion and Multi View Stereo, and we model a set of 3D templates of facade details. Next, we optimize the initial coarse model to enforce consistency between geometry and appearance (texture images). Then, building details are reconstructed by assembling templates on the textured faces of the coarse model. The 3D templates are automatically chosen and located by our optimization-based template assembly algorithm that balances image matching and structural regularity. In the results, we demonstrate how our framework can enrich the details of coarse models using various data sets.
Approximating Free-form Geometry with Height Fields for Manufacturing
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Herholz, Philipp; Matusik, Wojciech; Alexa, Marc; Olga Sorkine-Hornung and Michael Wimmer
We consider the problem of manufacturing free-form geometry with classical manufacturing techniques, such as mold casting or 3-axis milling. We determine a set of constraints that are necessary for manufacturability and then decompose and, if necessary, deform the shape to satisfy the constraints per segment. We show that many objects can be generated from a small number of (mold-)pieces if slight deformations are acceptable. We provide examples of actual molds and the resulting manufactured objects.
SpatialWhiteboard: A New Wearable Air-Writing Interaction with Kinect Sensor and Vibrating Ring Interface
(The Eurographics Association, 2015) Yeom, Kiwon; Han, Hyejin; Oh, Yoonsik; Kwon, Jeunghum; You, Bum-Jae; B. Solenthaler and E. Puppo
SpatialWhiteboard is a spatial finger writing system that enables complex spatial interactions through 3D handwriting via a Kinect sensor and vibrating ring interface. By incorporating depth and skin color information, we can directly separate the hand from the cluttered background. We can also accurately differentiate the fingertip from the hand by a mixture model of distance transforming and osculating circle. Users receive physical feedback in the form of vibrations from the wearable ring interface as their finger reaches a certain 3D position. Thus, it is now conceivable that anything people can do on contemporary touch based devices, they could do in midair with a pseudocontact interface.
Sample Elimination for Generating Poisson Disk Sample Sets
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Yuksel, Cem; Olga Sorkine-Hornung and Michael Wimmer
In this paper we describe sample elimination for generating Poisson disk sample sets with a desired size. We introduce a greedy sample elimination algorithm that assigns a weight to each sample in a given set and eliminates the ones with greater weights in order to pick a subset of a desired size with Poisson disk property without having to specify a Poisson disk radius. This new algorithm is simple, computationally efficient, and it can work in any sampling domain, producing sample sets with more pronounced blue noise characteristics than dart throwing. Most importantly, it allows unbiased progressive (adaptive) sampling and it scales better to high dimensions than previous methods. However, it cannot guarantee maximal coverage. We provide a statistical analysis of our algorithm in 2D and higher dimensions as well as results from our tests with different example applications.
Exploiting the Potential of Image Based Crowd Rendering
(The Eurographics Association, 2015) Izquierdo, Maria; Beacco, Alejandro; Pelechano, Nuria; Andujar, Carlos; B. Solenthaler and E. Puppo
Per-joint impostors have been used to achieve high performance when rendering thousands of agents, while still allowing us to blend animation. This provides interactively animated crowds and reduces the memory footprint compared to classic impostors. In this poster we exploit the potential of per joint impostors to further increase both visual quality and performance. The CAVAST framework for crowd simulation and rendering has been used to quantitatively evaluate our improvements with the profiling tools that it provides. Since different applications will have different requirements in terms of performance vs. visual quality, we have extended CAVAST with a new user interface to ease this process.
Eye Tracking Visualization
(The Eurographics Association, 2015) Burch, Michael; Blascheck, Tanja; Kurzhals, Kuno; Pflüger, Hermann; Raschke, Michael; Weiskopf, Daniel; Pfeiffer, Thies; M. Zwicker and C. Soler
Eye tracking has become a widely used method to analyze user behavior in marketing, neuroscience, human-computer interaction, and visualization research. Apart from measuring completion times and recording accuracy rates of correctly given answers during the performance of visual tasks in classical controlled user experiments, eye tracking-based evaluations provide additional information on how visual attention is distributed and changing for a presented stimulus. Due to the wide field of applications of eye tracking and various kinds of research questions, different approaches have been developed to analyze eye tracking data such as statistical algorithms (either descriptive or inferential), string editing algorithms, visualization-related techniques, and visual analytics techniques. Regardless of whether statistical or visual methods are used for eye tracking data analysis, a large amount of data generated during eye tracking experiments has to be handled.
Database-Assisted Object Retrieval for Real-Time 3D Reconstruction
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Li, Yangyan; Dai, Angela; Guibas, Leonidas; Nießner, Matthias; Olga Sorkine-Hornung and Michael Wimmer
In recent years, real-time 3D scanning technology has developed significantly and is now able to capture large environments with considerable accuracy. Unfortunately, the reconstructed geometry still suffers from incompleteness, due to occlusions and lack of view coverage, resulting in unsatisfactory reconstructions. In order to overcome these fundamental physical limitations, we present a novel reconstruction approach based on retrieving objects from a 3D shape database while scanning an environment in real-time. With this approach, we are able to replace scanned RGB-D data with complete, hand-modeled objects from shape databases. We align and scale retrieved models to the input data to obtain a high-quality virtual representation of the real-world environment that is quite faithful to the original geometry. In contrast to previous methods, we are able to retrieve objects in cluttered and noisy scenes even when the database contains only similar models, but no exact matches. In addition, we put a strong focus on object retrieval in an interactive scanning context —- our algorithm runs directly on 3D scanning data structures, and is able to query databases of thousands of models in an online fashion during scanning.
Privacy Protecting, Real-time Face Re-recognition
(The Eurographics Association, 2015) Niederberger, Thomas; Hegner, Robert; Hartmann, Andreas; Schuster, Guido M.; B. Solenthaler and E. Puppo
We present a novel system for recognizing human individuals walking past a depth camera that is compatible with privacy protecting laws. The system is developed to support the statistical analysis of movement patterns in indoor spaces. The system is able to re-recognize previously seen individuals but is also capable of recognizing that an individual has not been seen before. The system is designed in a privacy protecting way and does not rely on previously collected training data but rather collects data during run-time. The proposed system processes each image of an individual separately, but we also present a new approach that is based on combining several decisions into a single meta-decision in order to enhance classification performance.
Selective Degree Elevation for Multi-Sided Bézier Patches
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Smith, Jason; Schaefer, Scott; Olga Sorkine-Hornung and Michael Wimmer
This paper presents a method to selectively elevate the degree of an S-Patch of arbitrary dimension. We consider not only S-Patches with 2D domains but 3D and higher-dimensional domains as well, of which volumetric cage deformations are a subset. We show how to selectively insert control points of a higher degree patch into a lower degree patch while maintaining the polynomial reproduction order of the original patch. This process allows the user to elevate the degree of only one portion of the patch to add new degrees of freedom or maintain continuity with adjacent patches without elevating the degree of the entire patch, which could create far more degrees of freedom than necessary. Finally we show an application to cage-based deformations where we increase the number of control points by elevating the degree of a subset of cage faces. The result is a cage deformation with higher degree triangular Bézier functions on a subset of cage faces but no interior control points.

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