GRAPP 2018 Abstracts

Area 1 - Geometry and Modeling
Full Papers Short Papers
Area 2 - Rendering
Full Papers Short Papers
Area 3 - Animation and Simulation
Full Papers Short Papers
Area 4 - Interactive Environments
Full Papers Short Papers

Area 1 - Geometry and Modeling

Full Papers
Paper Nr: 6
Title:

Efficient Curvature-optimized G2-continuous Path Generation with Guaranteed Error Bound for 5-axis Machining
Authors:

Evgenia Selinger and Lars Linsen
Abstract: Automated machining with 5-axis robots require the generation of tool paths in form of positions of the tool tip and orientations of the tool at each position. Such a tool path can be described in form of two curves, one for the positional information and one for the orientational information, where the orientation is given by the vector that points from a point on the orientation curve to the respective point on the position curve. As the robots need to slow down for sharp turns, i.e., high curvatures in the tool path lead to slow processing, our goal is to generate tool paths with minimized curvatures and a guaranteed error bound. Starting from an initial tool path, which is given in form of polygonal representations of the position and orientation curves, we generate optimized versions of the curves in form of B-spline curves that lie within some error bounds of the input path. Our approach first computes an optimized version of the position curve within a tolerance band of the input curve. Based on this first step, the orientation curve needs to be updated to again fit the position curve. Then, the orientation curve is optimized using a similar approach as for the position curve, but the error bounds are given in form of tolerance frustums that define the tolerance in lead and tilt. For an efficient optimization procedure, our approach analyzes the input path and splits it into small (partially overlapping) groups before optimizing the position curve. The groups are categorized according to their geometric complexity and handled accordingly using two different optimization procedures. The simpler, but faster algorithm uses a local spline approximation, while the slower, but better algorithm uses a local sleeve approach. These algorithms are adapted to both the position and orientation curve optimization. Subsequently, the groups are combined into a 5-axis tool path in form of two G2-continuous B-spline curves over the same knot vector.
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Paper Nr: 23
Title:

Orientation Beautification of Reverse Engineered Models
Authors:

S. Gauthier, W. Puech, R. Bénière and G. Subsol
Abstract: Today, it has become more frequent and relatively easy to digitize the surface of 3D objects and then to reconstruct a boundary representation (B-Rep). However, the obtained results suffer from various inaccuracies, mainly caused by noisy data. In this paper, we present an efficient method to detect and rectify many regularities approximately present in an object. We propose to extract global parallelism and orthogonality constraints, then locally and independently adjust the geometric primitives (planes, cylinders, spheres, cones). We first retrieve orientations from primitives (normals, axes), then compute an orthonormal coordinate system. Finally, we adjust each primitive orientation according to spherical coordinates. Our objective is to design a fast and automatic method, which is seldom seen in reverse engineering. Experimental results applied on reverse engineered 3D meshes show the efficiency and the robustness of our proposed method.
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Paper Nr: 25
Title:

Transformation of the Beta Distribution for Color Transfer
Authors:

Hristina Hristova, Olivier Le Meur, Rémi Cozot and Kadi Bouatouch
Abstract: In this paper, we propose a novel transformation between two Beta distributions. Our transformation progressively and accurately reshapes an input Beta distribution into a target Beta distribution using four intermediate statistical transformations. The key idea of this paper is to adopt the Beta distribution to model the discrete distributions of color and light in images. We design a new Beta transformation which we apply in the context of color transfer between images. Experiments have shown that our method obtains more natural and less saturated results than results of recent state-of-the-art color transfer methods. Moreover, our results portray better both the target color palette and the target contrast.
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Paper Nr: 26
Title:

Block based Spectral Processing of Dense 3D Meshes using Orthogonal Iterations
Authors:

Aris S. Lalos, Gerasimos Arvanitis, Anastasios Dimas and Kostantinos Moustakas
Abstract: Spectral methods are widely used in geometry processing of 3D models. They rely on the projection of the mesh geometry on the basis defined by the eigenvectors of the graph Laplacian operator, becoming computationally prohibitive as the density of the models increases. In this paper, we propose a novel approach for supporting fast and efficient spectral processing of dense 3D meshes, ideally suited for real time compression and denoising scenarios. To achieve that, we apply the problem of tracking graph Laplacian eigenspaces via orthogonal iterations, exploiting potential spectral coherences between adjacent parts. To avoid perceptual distortions when a fixed number of eigenvectors is used for all the individual parts, we propose a flexible solution that automatically identifies the optimal subspace size for satisfying a given reconstruction quality constraint. Extensive simulations carried out with different 3D meshes in compression and denoising setups, showed that the proposed schemes are very fast alternatives of SVD based spectral processing while achieving at the same time similar or even better reconstruction quality. More importantly, the proposed approach can be employed by several other state of the art denoising methods as a preprocessing step, optimizing both their reconstruction quality and their computational complexity.
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Paper Nr: 39
Title:

A Procedural Model for Snake Skin Texture Generation
Authors:

Jefferson Magalhães Pinheiro and Marcelo Walter
Abstract: There are thousands of snake species in the world, many with intricate and distinct skin patterns. This diversity becomes a problem for users who need to create snake skin textures to apply on 3D models, as the difficulty for creating such complex patterns is considerable. We present a procedural model capable of synthesizing a wide range of texture skin patterns from snakes. Our model was derived from a visual assessment of a large number of snakes, and uses image processing as well as cellular automata to generate textures. Our results show good visual similarity with real skin found in snakes. The resulting textures can be used not only for computer graphics texturing, but also in education about snakes and their visual characteristics. We have also performed a user study to assess the usability of our tool. The score from the System Usability Scale was 85:8, suggesting a highly effective texturing tool.
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Short Papers
Paper Nr: 8
Title:

A Simple and Robust Approach to Computation of Meshes Intersection
Authors:

Věra Skorkovská, Ivana Kolingerová and Bedrich Benes
Abstract: Triangular meshes are important in many fields in both basic and applied research that rely on their correctness and accuracy. Many operations with meshes can lead to undesirable situations and the resulting models can be damaged and further unusable. Self-intersection and mesh-to-mesh intersection are types of operations that are often present and can cause such problems. We propose an accurate geometry-based method for local repair of intersecting meshes. The state-of-the-art methods either solve the problem inaccurately, or use methods such as arbitrary precision arithmetic or virtual perturbation to deal with the troublesome boundary cases. Our method represents a robust way to repair intersecting meshes accurately without the need to manipulate with the input data or to employ arbitrary precision arithmetic. The correct solution is obtained through a careful classification of the cases that could result from a numerical imprecision of the floating point arithmetic.
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Paper Nr: 13
Title:

Cinematographic and Geometric Criteria for Virtual Camera Path Generation for the Visualization of Shipwreck Data
Authors:

Katherine Davis, Vaibhav K. Viswanathan, Christopher M. Clark, Timothy Gambin and Zoë J. Wood
Abstract: This paper presents the use of cinematographic and geometric measures for determining the path of a virtual camera for the generation of computer graphics video sequences focused on showing an underwater shipwreck. This work rises from the applied challenge of mapping underwater shipwrecks, reconstructing a computer graphics model then creating an educational visualization of the wreck. The primary algorithm presented in this work computes the optimal camera pitch and height along a path utilizing a probabilistic roadmap (PRM) that weights nodes using a computational models of cinematographic and geometric principles. These principles were used to evaluate potential viewpoints and influence whether or not a view is used in the final path. Specifically, the algorithm uses a computational evaluation of the cinematographic ‘rule of thirds’ and a geometric evaluation of the model normals relative to the camera viewpoint. A user study of video output from the system suggests that our computed paths are ranked higher than simple circular or random paths and that the ‘rule of thirds’ is a more important criteria than the geometric principle explored.
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Paper Nr: 14
Title:

A Quartic Clough-Tocher Interpolant
Authors:

Xiang Fang and Stephen Mann
Abstract: In this paper we present a quartic version of the Clough-Tocher scheme for Hermite interpolation of functional data. This variation uses least squares to minimize discontinuities across the macro-patch boundaries, as well as adjusting one of the macro-boundary control points. The resulting surfaces have significantly better shape than a cubic version of Clough-Tocher that also used least squares to minimize discontinuities across patch boundaries. We compare our method to this cubic version of Clough-Tocher using shaded images and Gaussian curvature plots.
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Paper Nr: 12
Title:

Accurate Real-time Complex Cutting in Finite Element Modeling
Authors:

Tong Xin, Pieran Marris, Ana Mihut, Gary Ushaw and Graham Morgan
Abstract: This paper presents a real-time method for enacting accurate cutting of thin materials while retaining the physical accuracy of the underlying deformable material model. Our primary contribution is to offer a flexible real-time solution that can allow accurate cuts, re-cuts, curved cuts, sectioning (cutting out) on a deformable FEM model. Further contributions include improved handling of mesh element resizing after cutting for increasing material stability while balancing such resizing against real-time requirements. In this manner, we can represent precise cut incision (which may be curved or irregular) by subdividing mesh elements locally (at the cut point) while negating inappropriate (ill-shaped) elements with real-time level computational overhead and so avoiding modeling instabilities efficiently. We present the results of our solution that show the accuracy of the cutting method and illustrate timings for our optimised approach demonstrating its real-time qualities.
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Paper Nr: 28
Title:

Simplified Definition of Parameter Spaces of a Procedural Model using Sketch-based Interaction
Authors:

Johannes Merz, Roman Getto, Arjan Kuijper and Dieter W. Fellner
Abstract: This paper presents a novel technique to intuitively insert meta-parameters into a procedural model with the help of sketch-based interaction. The procedural model is represented in a GML (Generative Modeling Language) representation, which is a script language that focuses on the description of three-dimensional models. A GML model consists of a sequence of procedural modeling commands, for example extrusions. These are called with a set of local offset positions, which can be converted to global space and anchored in the surface mesh by finding reference vertices on the mesh. The system uses a deformation technique to deform the surface of the model. During the deformation, the reference vertices provide the global offset positions, whose path can be approximated by a B-spline. Exchanging the initial values of the commands by this B-spline, defines a continuous parameter space of the meta-parameter. The deformation process is supported by a mesh segmentation to create pre-defined deformation targets. Using sketch-based methods, these can be adapted to the user’s needs. The results show that the system closely imitates the deformation with the help of the modeling commands. Furthermore, the system was evaluated to be intuitive and easy to use.
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Paper Nr: 29
Title:

Tone Mapping HDR Panoramas for Viewing in Head Mounted Displays
Authors:

Miguel Melo, Kadi Bouatouch, Maximino Bessa, Hugo Coelho, Remi Cozot and Alan Chalmers
Abstract: Head-mounted displays enable a user to view a complete environment as if he/she was there; providing an immersive experience. However, the lighting in a full environment can vary significantly. Panoramic images captured with conventional, Low Dynamic Range (LDR), imaging of scenes with a large range of lighting conditions, can include areas of under- or over-exposed pixels. High Dynamic Range (HDR) imaging, on the other hand, is able to capture the full range of detail in a scene. However, HMDs are not currently HDR and thus the HDR panorama needs to be tone mapped before it can be displayed on the LDR HMD. While a large number of tone mapping operators have been proposed in the last 25 years, these were not designed for panoramic images, or for use with HMDs. This paper undertakes a two part subjective study to investigate which of the current, state-of-the-art tone mappers is most suitable for use with HMDs.
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Paper Nr: 34
Title:

Creating 3D Human Character Mesh Prototypes from a Single Front-view Sketch
Authors:

Shaikah Bakerman, Rufino R. Ansara and Chris Joslin
Abstract: 3D character modeling, a vital part in film and video game production, is a process that starts by blocking out the basic geometry of a character, which is then transformed into a detailed mesh. This process can be a long and daunting task to novice modelers. To facilitate this process, we developed a sketch-based modeling system that constructs the basic 3D geometry of a human character based on a single front-view sketch and minimal user interaction. The objective of this system is to help novice 3D artists by automating the initial phase of the modeling process with an intuitive user interface, and to construct a mesh that conforms to common modeling techniques. We conducted a user study to evaluate the system’s user interface and produced mesh. Results show that our interface is intuitive, easy to use and produces accurate meshes that can facilitate the modeling process. Moreover, the processing time of our system is faster than the average time it takes artists to manually construct a similar mesh.
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Area 2 - Rendering

Full Papers
Paper Nr: 15
Title:

Interactive Hyper Spectral Image Rendering on GPU
Authors:

Romain Hoarau, Eric Coiro, Sébastien Thon and Romain Raffin
Abstract: In this paper, we describe a framework focused on spectral images rendering. The rendering of a such image leads us to three major issues: the computation time, the footprint of the spectral image, and the memory consumption of the algorithm. The computation time can be drastically reduced by the use of GPUs, however, their memory capacity and bandwidth (compared to their compute power) are limited. When the spectral dimension of the image will raise, the straightforward approach of the Path Tracing will lead us to high memory consumption and latency problems. To overcome these problems, we propose the DPEPT (Deferred Path Evaluation Path Tracing) which consists in decoupling the path evaluation from the path generation. This technique reduces the memory latency and consumption of the Path Tracing. It allows us to use an efficient wavelength samples batches parallelization pattern to optimize the path evaluation step and outperforms the straightforward approach when the spectral resolution of the simulated image increases.
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Paper Nr: 22
Title:

Visibility based WSPD for Global Illumination
Authors:

M. Maria, N. Mustafa, T. Bardoux, J. Defaye and V. Biri
Abstract: In the context of rendering production, and especially for indirect diffuse global illumination, many-light techniques can be used to quickly render noise free images. In this paper, we propose a view-independent algorithm, based on Well Separated Pair Decomposition (WSPD), to handle efficiently clustering of virtual point lights. Our clustering, the Visibility based WSPD (V-WSPD) consider both geometric and visibility information of two sets of points, allowing an improved rendering time with a similar image quality.
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Paper Nr: 45
Title:

Removing Monte Carlo Noise with Compressed Sensing and Feature Information
Authors:

Changwen Zheng and Yu Liu
Abstract: Monte Carlo renderings suffer noise artifacts at low sampling rates. In this paper, a novel rendering algorithm that combines compressed sensing (CS) and feature buffers is proposed to remove the noise. First, in the sampling stage, the image is divided into patches that each one corresponds to a fixed resolution. Second, each pixel value in the patch is reconstructed by calculating the related coefficients in a transform domain, which is achieved by a CS-based algorithm. Then in the reconstruction stage, each pixel is filtered over a set of filters that use a combination of colors and features. The difference between the reconstructed value and the filtered value is used as the estimated reconstruction error. Finally, a weighted average of two filters that return the smallest error is computed to minimize output error. The experimental results show that the new algorithm outperforms previous methods both in visual image quality and numerical error.
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Short Papers
Paper Nr: 33
Title:

A Hybrid CPU-GPU Scalable Strategy for Multi-resolution Rendering of Large Digital Elevation Models with Borders and Holes
Authors:

Andrey Rodrigues and Waldemar Celes
Abstract: Efficient rendering of large digital elevation models remains as a challenge for real-time applications, especially if those models contain irregular borders and holes. First, direct use of hardware tessellation has limited scalability; although the graphics hardware is capable of controlling the resolution of patches in a very efficient manner, the whole patch data must be loaded in memory. Second, previous techniques restrict elevation data resolution and do not handle irregular border or holes. In this paper, we propose an efficient and scalable hybrid CPU-GPU algorithm for rendering large digital elevation models. Our proposal effectively combines GPU tessellation with CPU tile management, taking full advantage of GPU processing capabilities while maintaining graphics-memory use under practical limits. Our proposal also handles models with irregular borders and holes. Additionally, we present a technique to manage level of detail of aerial imagery mapped on top of elevation models. Both geometry and texture level of detail management run independently, and tiles are combined with no need to load extra data.
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Paper Nr: 40
Title:

Data-driven Enhancement of SVBRDF Reflectance Data
Authors:

Heinz Christian Steinhausen, Dennis den Brok, Sebastian Merzbach, Michael Weinmann and Reinhard Klein
Abstract: Analytical SVBRDF representations are widely used to represent spatially varying material appearance depending on view and light configurations. State-of-the-art industry-grade SVBRDF acquisition devices allow the acquisition within several minutes. For many materials with a surface reflectance behavior exhibiting complex effects of light exchange such as inter-reflections, self-occlusions or local subsurface scattering, SVBRDFs cannot accurately capture material appearance. We therefore propose a method to transform SVBRDF acquisition devices to full BTF acquisition devices. To this end, we use data-driven linear models obtained from a database of BTFs captured with a traditional BTF acquisition device in order to reconstruct high-resolution BTFs from the SVBRDF acquisition devices’ sparse measurements. We deal with the high degree of sparsity using Tikhonov regularization. In our evaluation, we validate our approach on several materials and show that BTF-like material appearance can be generated from SVBRDF measurements in the range of several minutes.
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Paper Nr: 43
Title:

Denoising Monte Carlo Renderings based on a Robust High-order Function
Authors:

Yu Liu, Changwen Zheng and Hongliang Yuan
Abstract: Image space rendering methods are efficient at removing Monte Carlo noise. However, a major challenge is optimizing the bandwidth to denoise images while preserving their fine details. In this paper, a high-order function is proposed to leverage the correlation between features and pixel colors. We consider feature buffers to fit data while computing regression weights using pixel colors. A collaborative prefiltering framework is first proposed to denoise features. The input pixel colors are then denoised using a guided image filter that maintains fine details in the output by constructing a guidance image using features. The optimal bandwidth is selected through an iterative error estimation process performed at multiple pixels to smooth the details. Finally, we adaptively select center pixels to build our regression models and vary the window size to reduce computational overhead. Experimental results showed that the new approach outperforms competing methods in terms of the quality of the visual image and the numerical error incurred.
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Paper Nr: 44
Title:

Sparse Sampling for Real-time Ray Tracing
Authors:

Timo Viitanen, Matias Koskela, Kalle Immonen, Markku Mäkitalo, Pekka Jääskeläinen and Jarmo Takala
Abstract: Ray tracing is an interesting rendering technique, but remains too slow for real-time applications. There are various algorithmic methods to speed up ray tracing through uneven screen-space sampling, e.g., foveated rendering where sampling is directed by eye tracking. Uneven sampling methods tend to require at least one sample per pixel, limiting their use in real-time rendering. We review recent work on image reconstruction from arbitrarily distributed samples, and argue that these will play major role in the future of real-time ray tracing, allowing a larger fraction of samples to be focused on regions of interest. Potential implementation approaches and challenges are discussed.
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Area 3 - Animation and Simulation

Full Papers
Paper Nr: 1
Title:

SheetAnim - From Model Sheets to 2D Hand-drawn Character Animation
Authors:

Heena Gupta and Parag Chaudhuri
Abstract: We present an intuitive method to create 2D hand-drawn character animation suitable for novice animators. Given the 2D model sheet of the character that shows how the character looks from the front and side, our method can generate sketched views of the character from any direction, using the sketch stroke style used in the model sheet. Subsequently, our system can generate an animation of the character using motion capture data, and render it using the same sketched strokes. Our method is not only able to reproduce the sketch stroke style, but also the colours and other character details that the animator adds to the model sheet. The method can resolve occlusion correctly, both due to moving body parts and change in orientation of the character with respect to the camera. The animator can interactively change the sketch style, colours or other details, at any frame, as required. The animation generated by our method has the fluid style of hand sketched animation, and provides a very good starting point for novice animators that can be then improved to create the final, desired animation.
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Paper Nr: 2
Title:

Accelerated Simulation of Brittle Objects for Interactive Applications
Authors:

Philippe Meseure, Xavier Skapin, Emmanuelle Darles and Guilhem Delaitre
Abstract: This article presents a model that aims at computing deformation and simulating fractures. To allow the use of linear elasticity in small displacements for deformation of a brittle object while still enabling any rigid motion, a rigid reference is computed using the Shape Matching method and all displacements are evaluated with respect to this reference. Fractures are handled using a stress tensor computed at each vertex of the object’s 3D mesh. Some accelerations are proposed, that allow a faster determination of fracture areas and a fast processing of new connected components.
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Short Papers
Paper Nr: 17
Title:

A Topological-Geometrical Pipeline for 3D Cracking-like Phenomena
Authors:

Jérémy Riffet, Nicolas Castagne, Emmanuelle Darles and Annie Luciani
Abstract: Animation of one-to-many phenomena (fractures, tears, breaks, cracks…) is challenging. This article builds over recent works that proposed a 3-stages modelling and simulation pipeline, made of a cascade of models: geometry-free physical model → explicit modelling of the evolving topology → geometrical model. On the Physics’ side, in the framework of masses-interactions network modelling, the article extends the recent Splitting-MAT method, where the physical splits occur onto the material points, toward 3 dimensional volume models. Downstream, it introduces a topo-geometrical pipeline adapted to this upstream split-on-the-masses property. Experiments, and analysis of the complexity of the topo-geometrical part, show that, while offering constructible and manageable means, separating Physical, Topological and Geometrical aspects in the 3-stages pipeline enables a rich variety of one-to-many dynamics, with good efficiency.
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Paper Nr: 35
Title:

Interactive Anisotropic Tearing of Elastic Solids
Authors:

Omar Hesham, Chris Joslin and Rufino R. Ansara
Abstract: Dynamic models to simulate tearing of soft elastic bodies are an essential element of various medical and surgical training simulators. These models are also finding increased use in film and gaming applications, where control of the quality and style of the final output is highly valued. There is a general lack of models specifically designed to control tearing patterns, and in this paper, we present our work towards a soft-body tearing method that provides simple parametrizations to control the tear independently from the elastic properties of the soft body simulation. Our parameters can influence how clean-cut or jagged the tear is, in addition to allowing anisotropic influence using an embedded fibre model in the elastic body. We also aim for a real-time implementation suitable for interactive environments. Our meshless solution is discussed in a context that is aware of the importance of unified physics solvers.
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Area 4 - Interactive Environments

Full Papers
Paper Nr: 3
Title:

Optical-inertial Synchronization of MoCap Suit with Single Camera Setup for Reliable Position Tracking
Authors:

Adam Riečický, Martin Madaras, Michal Piovarci and Roman Durikovic
Abstract: We propose a method for synchronization of an inertial motion capture suit and a single camera optical setup. Proposed synchronization is based on an iterative optimization of an energy potential in image space, minimizing the error between the camera image and a rendered virtual representation of the scene. For each frame, an input skeleton pose from the mocap suit is used to render a silhouette of a subject. Moreover, the local neighborhood around the last known position is searched by matching the silhouette to the distance transform representation of the camera image based on Chamfer matching. Using the combination of the camera tracking and the inertial motion capture suit, it is possible to retrieve the position of the joints that are hidden from the camera view. Moreover, it is possible to capture the position even if it cannot be captured by the suit sensors. Our system can be used for both real-time tracking and off-line post-processing of already captured mocap data.
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Paper Nr: 4
Title:

Sensor-fusion-based Trajectory Reconstruction for Mobile Devices
Authors:

Jielei Zhang, Jie Feng and Bingfeng Zhou
Abstract: In this paper, we present a novel sensor-fusion method that reconstructs trajectory of mobile devices from MEMS inertial measurement unit (IMU). In trajectory reconstruction, the position estimation suffers seriously from the errors in the raw MEMS data, e.g. accelerometer signal, especially after its second-order integration over time. To eliminate the influence of the errors, a new error model is proposed for MEMS devices. The error model consists of two components, i.e. noise and bias, corresponding to different types of errors. For the noise component, a low-pass filter with down sampling is applied to reduce the inherent noise in the data. For the bias component, an algorithm is designed to detect the events of movement in a manner of sensor fusion. Then, the denoised data is further calibrated, according to different types of events to remove the bias. We apply our trajectory reconstruction method on a quadrotor drone with low-cost MEMS IMU devices, and experiments show the effectiveness of the method.
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Paper Nr: 24
Title:

Retrieving 3D Objects with Articulated Limbs by Depth Image Input
Authors:

Jun-Yang Lin, May-Fang She, Ming-Han Tsai, I-Chen Lin, Yo-Chung Lau and Hsu-Hang Liu
Abstract: Existing 3D model retrieval approaches usually implicitly assume that the target models are rigid-body. When they are applied to retrieving articulated models, the retrieved results are substantially influenced by the model postures. This paper presents a novel approach to retrieve 3D models from a database based on one or few input depth images. While related methods compared the inputs with whole shapes of 3D model projections at certain viewpoints, the proposed method extracts the limbs and torso regions from projections and analyzes the features of local regions. The use of both global and local features can alleviate the disturbance of model postures in model retrieval. Therefore, the system can retrieve models of an identical category but in different postures. Our experiments demonstrate that this approach can efficiently retrieve relevant models within a second, and it provides higher retrieval accuracy than those of compared methods for rigid 3D models or models with articulated limbs.
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Paper Nr: 47
Title:

Generic Caching Library and Its Use for VTK-based Real-time Simulation and Visualization Systems
Authors:

Lukáš Hruda and Josef Kohout
Abstract: In many visualization applications, physics-based simulations are so time consuming that desired real-time manipulation with the visual content is not possible. Very often this time consumption can be prevented by using some kind of caching since many of the processes in these simulations repeat with the same inputs producing the same output. Creating a simple caching mechanism for cases where the order of the data repetition is known in advance is not a very difficult task. But in reality, the data repetition is often unpredictable and in such cases some more sophisticated caching mechanism has to be used. This paper presents a novel generic caching library for C++ language that is suitable for such situations. It also presents a wrapper that simplifies the usage of this library in the applications based on the popular VTK visualization tool. Our experiments show that the developed library can speed up VTK based visualizations significantly with a minimal effort.
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Short Papers
Paper Nr: 36
Title:

Virtual Exploration: Seated versus Standing
Authors:

Noah Coomer, Joshua Ladd and Betsy Williams
Abstract: Virtual environments are often explored standing up. The purpose of this work is to understand if standing exploration has an advantage over seated exploration. Thus, we present an experiment that directly compares subjects’ spatial awareness when locomoting with a joystick when they are physically standing up versus sitting down. In both conditions, virtual rotations matched the physical rotations of the subject and the joystick was only used for translations through the virtual environment. In the seated condition, users sat in an armless swivel office chair. Our results indicated that there was no difference between the two conditions, sitting and standing. However, this result is interesting and might compel more virtual environment developers to encourage their users to sit in a comfortable swivel chair. As an additional finding to our study, we find a significant difference between the performance of males versus females and gamers versus non–gamers.
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Paper Nr: 42
Title:

Mixed Reality Experience - How to Use a Virtual (TV) Studio for Demonstration of Virtual Reality Applications
Authors:

Jens Herder, Philipp Ladwig, Kai Vermeegen, Dennis Hergert, Florian Busch, Kevin Klever, Sebastian Holthausen and Bektur Ryskeldiev
Abstract: The article discusses the question of “How to convey the experience in a virtual environment to third parties?” and explains the different technical implementations which can be used for live streaming and recording of a mixed reality experience. The real-world applications of our approach include education, entertainment, e-sports, tutorials, and cinematic trailers, which can benefit from our research by finding a suitable solution for their needs. We explain and outline our Mixed Reality systems as well as discuss the experience of recorded demonstrations of different VR applications, including the need for calibrated camera lens parameters based on realtime encoder values.
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Paper Nr: 50
Title:

Deep Light Source Estimation for Mixed Reality
Authors:

Bruno Augusto Dorta Marques, Rafael Rego Drumond, Cristina Nader Vasconcelos and Esteban Clua
Abstract: Mixed reality is the union of virtual and real elements in a single scene. In this composition, of real and virtual elements, perceptual discrepancies in the illumination of objects may occur. We call these discrepancies the illumination mismatch problem. Recovering the lighting information from a real scene is a difficult task. Usually, such task requires prior knowledge of the scene, such as the scene geometry and special measuring equipment. We present a deep learning based technique that estimates point light source position from a single color image. The estimated light source position is used to create a composite image containing both the real and virtual environments. The proposed technique allows the final composite image to have consistent illumination between the real and virtual worlds, effectively reducing the effects of the illumination mismatch in Mixed Reality applications.
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Paper Nr: 7
Title:

Comparison of Movements in a Virtual Reality Mirror Box Therapy for Treatment of Lower Limb Phantom Pain
Authors:

Bartal Henriksen, Ronni Nedergaard Nielsen, Martin Kraus and Bo Geng
Abstract: Many patients experience Phantom Limb Pain (PLP) after an amputation. Traditional Mirror Box Therapy (MBT) has proven efficient for some patients, but the movements in MBT are physically limited, for lower limb amputees. In this work, we investigated how anti-symmetrical mirroring compares to regular mirroring in Virtual Reality (VR) MBT for lower limb amputees, as natural leg movements are anti-symmetrical, like walking, running, and cycling. To motivate the patients, a game was developed that uses cycling and swinging movements. We implemented the required movements into a goal-oriented game where the patient must fly a gyrocopter through goal areas. The experiment was implemented as a within-subject design, where the participants had to try three versions of the game and give preferential feedback. The findings showed that the cycling version was more exhausting than the anti-symmetrical and symmetrical swinging versions. Furthermore, we discovered that the required cycling motions were too difficult and tiresome to do over a longer period of time. On the other hand, we found that it is possible to use anti-symmetrical swinging of legs in VR MBT.
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Paper Nr: 21
Title:

PEEK - An LSTM Recurrent Network for Motion Classification from Sparse Data
Authors:

Rafael Rego Drumond, Bruno A. Dorta Marques, Cristina Nader Vasconcelos and Esteban Clua
Abstract: Games and other applications are exploring many different modes of interaction in order to create intuitive interfaces, such as touch screens, motion controllers, recognition of gesture or body movements among many others. In that direction, human motion is being captured by different sensors, such as accelerometers, gyroscopes, heat sensors and cameras. However, there is still room for investigation the analysis of motion data captured from low-cost sensors. This article explores the extent to which a full body motion classification can be achieved by observing only sparse data captured by two separate inherent wereable measurement unit (IMU) sensors. For that, we developed a novel Recurrent Neural Network topology based on Long Short-Term Memory cells (LSTMs) that are able to classify motions sequences of different sizes. Using cross-validation tests, our model achieves an overall accuracy of 96% which is quite significant considering that the raw data used was obtained using only 2 simple and accessible IMU sensors capturing arms movements. We also built and made public a motion database constructed by capturing sparse data from 11 actors performing five different actions. For comparison with existent methods, other deep learning approaches for sequence evaluation (more specifically, based on convolutional neural networks), were adapted to our problem and evaluated.
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