EG UK Theory and Practice of Computer Graphics 2012

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    Light Clustering for Dynamic Image Based Lighting
    (The Eurographics Association, 2012) Staton, Sam; Debattista, Kurt; Bashford-Rogers, Thomas; Chalmers, Alan; Hamish Carr and Silvester Czanner
    High Dynamic Range (HDR) imagery has made it possible to relight virtual objects accurately with the captured lighting. This technique, called Image Based Lighting (IBL), is a commonly used to render scenes using real-world illumination. IBL has mostly been limited to static scenes due to limitations of HDR capture. However, recently there has been progress on developing devices which can capture HDR video sequences. These can be also be used to light virtual environments dynamically. If existing IBL algorithms are applied to this dynamic problem, temporal artifacts viewed as flickering can often arise due to samples being selected from different parts of the environment in consecutive frames. In this paper we present a method for efficiently rendering virtual scenarios with such captured sequences based on spatial and temporal clustering. Our proposed Dynamic IBL (DIBL) method improves temporal quality by suppressing flickering, and we demonstrate the application to fast previews of scenes lit by video environment maps.
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    Simplified User Interface for Architectural Reconstruction
    (The Eurographics Association, 2012) Wanner, Fabian; Pece, Fabrizio; Kautz, Jan; Hamish Carr and Silvester Czanner
    We present a user-driven reconstruction system for the creation of 3D models of buildings from photographs. The structural properties of buildings, such as parallel and repeated elements, are used to allow the user to create efficiently an accurate 3D structure of different building types. An intuitive interface guides the user through the reconstruction process, which uses a set of input images and a 3D point cloud. The system aims to minimise the user input by recognising imprecise interaction and ensuring photo consistency.
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    Large Scale Pedestrian Multi-Simulation for a Decision Support Tool
    (The Eurographics Association, 2012) Karmakharm, Twin; Richmond, Paul; Hamish Carr and Silvester Czanner
    Ability to simulate pedestrian behaviour on a large scale is essential in identifying potential dangers in public spaces during an evacuation. Multiple designs must be tested with varying parameters and run multiple times to achieve statistical significance due to the model's stochastic nature. In this short paper, we describe our prototype decision support tool that enables concurrent simulation on GPU-enabled computers by merging them to increase efficiency and dispatching simulation jobs across multiple machines on the network. Preliminary results with our GPU-optimised model have been shown to run at faster than real-time simulation speeds.
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    Backwards Compatible JPEG Stereoscopic High Dynamic Range Imaging
    (The Eurographics Association, 2012) Selmanovic, Elmedin; Debattista, Kurt; Bashford-Rogers, Thomas; Chalmers, Alan; Hamish Carr and Silvester Czanner
    In this paper we introduce Stereoscopic High Dynamic Range (SHDR) Imagery which is a novel tecnique that combines high dynamic range imaging and stereoscopy. Stereoscopic imaging captures two images representing the views of both eyes and allows for better depth perception. High dynamic range (HDR) imaging is an emerging technology which allows the capture, storage and display of real world lighting as opposed to traditional imagery which only captures a restricted range of light due to limitation in hardware capture and displays. HDR provides better contrast and more natural looking scenes. One of the main challenges that needs to be overcome for SHDR to be successful is an efficient storage format that compresses the very large sizes obtained by SHDR if left uncompressed; stereoscopic imaging requires the storage of two images and uncompressed HDR requires the storage of a floating point value per colour channel per pixel. In this paper we present a number of SHDR compression methods that are backward compatible with traditional JPEG, stereo JPEG and JPEG-HDR. The proposed methods can encode SHDR content to little more than that of a traditional LDR image and the backward compatibility property encourages early adopters to adopt the format since their content will still be viewable by any of the legacy viewers.
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    Path Tracing on Massively Parallel Neuromorphic Hardware
    (The Eurographics Association, 2012) Richmond, Paul; Allerton, David J.; Hamish Carr and Silvester Czanner
    Ray tracing on parallel hardware has recently benefit from significant advances in the graphics hardware and associated software tools. Despite this, the SIMD nature of graphics card architectures is only able to perform well on groups of coherent rays which exhibit little in the way of divergence. This paper presents SpiNNaker, a massively parallel system based on low power ARM cores, as an architecture suitable for ray tracing applications. The asynchronous design allows us to demonstrate a linear performance increase with respect to the number of cores. The performance perWatt ratio achieved within the fixed point path tracing example presented is far greater than that of a multi-core CPU and similar to that of a GPU under optimal conditions.
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    Analyzing and Visualizing Multivariate Volumetric Scalar Data and Their Uncertainties
    (The Eurographics Association, 2012) Ma, Ji; Murphy, D.; O'Mathuna, C.; Hayes, M.; Provan, G.; Hamish Carr and Silvester Czanner
    Data sets from the real world and most scientific simulations are known to be imperfect, often incorporating uncertainty information. Exploration and analysis of such variable data can lead to inaccurate or even incorrect results and inferences. As a powerful tool to communicate the data with users, an effective visualization system should present and inform users of the uncertainty information existing in the data. While some research has been conducted on visualizing uncertainty in spatio-temporal data and univariate data, little work has been reported on multivariate data. In addition, there are two main disadvantages in the existing uncertainty visualization methods for volumetric data. First, they rely heavily on the human perceptual system to recognize the uncertainty information, lacking the capability to depict them quantitatively. Second, they often present large amounts of diverse information in a single display, which may result in visual clutter and occlusion. In this paper, we present our hybrid framework that combines both information visualization techniques and scientific visualization techniques together to allow users to interactively specify features of interest, quantitatively explore and analyze the multivariate volumetric data and their uncertainties as well as localize features in the 3D object space. In comparison with those existing methods, we argue that our method not only allows users to quantitatively visualize the uncertainties within multivariate volumetric data, but also yields a clearer data presentation and facilitates a greater level of visual data analysis. We demonstrate the effectiveness of our framework by reporting a case study from the OpenGGCM (Open Geospace General Circulation Model) simulation in space science application domain.
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    Computing Curve Skeletons from Medial Surfaces of 3D Shapes
    (The Eurographics Association, 2012) Telea, Alexandru; Jalba, Andrei C.; Hamish Carr and Silvester Czanner
    Skeletons are powerful shape descriptors with many applications in shape processing, reconstruction and matching. In this paper we show that in 3D, curve skeletons can be extracted from surface skeletons in the same manner as surface skeletons can be computed from 3D object representations. Thus, the curve skeleton is conceptually the result of a recursion applied twice to a given 3D shape. To compute them, we propose an explicit advection of the surface skeleton in the implicitly-computed gradient of its distance-transform field. Through this process, surface skeleton points collapse into the sought curve skeleton. As a side result, we show how to reconstruct accurate and smooth surface skeletons from point-cloud representations thereof. Finally, we compare our method to existing state-of-the-art approaches.
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    Advanced, Automatic Stream Surface Seeding and Filtering
    (The Eurographics Association, 2012) Edmunds, Matt; Laramee, Robert S.; Chen, Guoning; Zhang, Eugene; Max, Nelson; Hamish Carr and Silvester Czanner
    The placement or seeding of stream surfaces in 3D flow fields faces a number of challenges. These challenges include perception, occlusion, and the appropriate representation of flow characteristics. A variety of streamline seeding approaches exist, little corresponding work is presented for stream surfaces. We present a novel automatic stream surface seeding and filtering algorithm. Our approach is designed to capture the characteristics of the flow utilizing illustrative techniques to alleviate occlusion and provide options for filtering. We define and prioritize a set of seeding curves at the domain boundaries from isolines computed from a derived scalar field. We detail the generation of an initial set of surfaces from the set of seeding curves, and discuss a technique for effective surface termination. We then present an algorithm that automatically seeds new interior surfaces, to represent locations not captured by the boundary seeding, at a user specified separation from the initial surface set. The results demonstrate satisfactory domain coverage and effective visualizations on a variety of simulations.
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    Visualizing a Spherical Geological Discrete Element Model of Fault Evolution
    (The Eurographics Association, 2012) Longshaw, Stephen M.; Turner, Martin J.; Finch, Emma; Hamish Carr and Silvester Czanner
    Discrete Element Modelling (DEM) is a numerical technique that uses a system of interacting discrete bodies to simulate the movement of material being exposed to external forces. This technique is often used to simulate granular systems; however by adding further elements that inter-connect the bodies, it can be used to simulate the deformation of a large volume of material. This method has precedent for use in the Earth Sciences and recently, with the increase of available computing power, it has been put to good use simulating the evolution of extensional faults in large scale crustal experiments that involve over half a million individual spherical bodies. An interactive environment that provides high quality rendering is presented, showing that interactivity is key in allowing the intelligent application of visualization methods such as colour-mapping and visibility thresholds in order to extract fault information from a geological DEM. It is also shown that glyph representation alone is not sufficient to provide full insight into the complex three dimensional geometries of the faults found within the model. To overcome this, a novel use of the MetaBall method is described, which results in implicit surface representations of sphere sub-sets. The surfaces produced are shown to provide greater insight into the faults found within the data but also raise questions as to their meaning.
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    Fast Scalable k-NN Computation for Very Large Point Clouds
    (The Eurographics Association, 2012) Spina, Sandro; Debattista, Kurt; Bugeja, Keith; Chalmers, Alan; Hamish Carr and Silvester Czanner
    The process of reconstructing virtual representations of large real-world sites is traditionally carried out through the use of laser scanning technology. Recent advances in these technologies led to improvements in precision and accuracy and higher sampling rates. State of the art laser scanners are capable of acquiring around a million points per second, generating enormous point cloud data sets. These data sets are usually cleaned through the application of numerous post-processing algorithms, like normal determination, clustering and noise removal. A common factor in these algorithms is the recurring need for the computation of point neighborhoods, usually by applying algorithms to compute the k-nearest neighbours of each point. The majority of these algorithms work under the assumption that the data sets operated on can fit in main memory, while others take into account the size of the data sets and are thus designed to keep data on disk. We present a hybrid approach which exploits the spatial locality of point clusters in the point cloud and loads them in system memory on demand by taking advantage of paged virtual memory in modern operating systems. In this way, we maximize processor utilization while keeping I/O overheads to a minimum. We evaluate our approach on point cloud sizes ranging from 50K to 333M points on machines with 1GB, 2GB, 4GB and 8GB of system memory.
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    ViewFusion: Correlating Structure and Activity Views for Execution Traces
    (The Eurographics Association, 2012) Trümper, Jonas; Telea, Alexandru; Döllner, Jürgen; Hamish Carr and Silvester Czanner
    Visualization of data on structure and related temporal activity supports the analysis of correlations between the two types of data. This is typically done by linked views. This has shortcomings with respect to efficient space usage and makes mapping the effect of user input into one view into the other view difficult. We propose here a novel, space-efficient technique that 'fuses' the two information spaces - structure and activity - in one view. We base our technique on the idea that user interaction should be simple, yet easy to understand and follow. We apply our technique, implemented in a prototype tool, for the understanding of software engineering datasets, namely static structure and execution traces of the Chromium web browser.
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    Using Quest3D to Develop VES: a Tool for Enhancing Electrical Safety and Design in the Built Environment
    (The Eurographics Association, 2012) Barrett, Martin; Blackledge, J. M.; Hamish Carr and Silvester Czanner
    This paper presents a novel desktop virtual reality model titled Virtual Electrical Services (VES), developed to en-hance electrical safety and design in the built environment. The model developed using Quest3D has the potential to be used as an industry design tool or as an educational tool for third level students and represents a significant watershed in how electrical services engineers can potentially design buildings and interpret their design deci-sions. A description of the software development process of the virtual reality model is presented along with the applications that were developed within the model. Based on the early implementation of this prototype model, it would appear electrical services engineers perceive the prototype to be a useful tool and were receptive to using VES as a learning and design tool.
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    On the Fractal Behaviour of AA Patterns
    (The Eurographics Association, 2012) Ahmed, Abdalla G. M.; Hamish Carr and Silvester Czanner
    ''AA Patterns'' is a recently discovered kind of algorithmic art in the form of pixel patterns; where each pixel in a 2D bitmap is set or unset according to a simple test applied to its coordinates pair. In spite of their iterationfree algorithm, AA Patterns exhibit signs which suggest some relation to fractals. This paper investigates this relationship, and reveals a new fractal which comes from an iteration-free process.
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    Hardware Accelerated Medical Data Visualisation on the Web
    (The Eurographics Association, 2012) Wei, Hui; Clapworthy, Gordon J.; Liu, E.; Zhao, Y.; McFarlane, N. M. B.; Hamish Carr and Silvester Czanner
    This paper proposes a way to develop high-quality real-time web-based medical 3D data visualisation. Isosurface extraction is used as an example to discuss how to use programmable Graphics Processing Units (GPUs) and shaders to improve rendering performance on the web. The method is designed to reduce data transmission. When data is ready, the performance penalty can be considered negligible. A method to estimate memory usage to balance client memory limitation and rendering quality is also described. A way of using the frame rate to measure performance on the web is suggested, which could be used in future web visualisation.
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    Physical and Perceptual Limitations of a Projector-based High Dynamic Range Display
    (The Eurographics Association, 2012) Wanat, Robert; Petit, Josselin; Mantiuk, Rafal; Hamish Carr and Silvester Czanner
    High dynamic range (HDR) displays capable of reproducing scenes of high luminance (exceeding 2,000 cd/m2) and contrast (more than 10,000:1) are a useful tool for research on visual performance, image quality or colour appearance. In this paper, we describe a projector-based HDR display, giving details on its hardware components and software for driving and calibrating the display. We report the colorimetric properties of the display: the colour reproduction accuracy, colour gamut and local contrast dependent on the size of displayed checkerboard pattern. To verify whether our display can produce local contrast inducing the colour that appears perfectly black to the observer, we conducted an experiment with human observers. Our results indicate that for the test pattern, the effective local contrast of our display (2500:1) is sufficient to produce perfectly black colour, which requires a contrast between 1300:1 and 2400:1.