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In this position paper we discuss the usage of various interaction technologies with focus on the presentations of 3D visualizations involving a presenter and an audience. While an interaction technique is commonly evaluated from a user perspective, we want to shift the focus from a sole analysis of the naturalness and the ease-of-use for the user, to focus on how expressive and understandable the interaction technique is when witnessed by the audience. The interaction process itself can be considered to be a communication channel and a more expressive interaction technique might make it easier for the audience to comprehend the presentation. Thus, while some natural interaction techniques for interactive visualization are easy to perform by the presenter, they may be less beneficial when interacting with the visualization in front of (and for) an audience. Our observations indicate that the suitability of an interaction technique as a communication channel is highly dependent on the setting in which the interaction takes place. Therefore, we analyze different presentation scenarios in an exemplary fashion and discuss how beneficial and comprehensive the involved techniques are for the audience. We argue that interaction techniques complement the visualization in an interactive presentation scenario as they also serve as an important communication channel, and should therefore also be observed from an audience perspective rather than exclusively a user perspective.

Data acquired from ultrasound examinations is of interest not only for the physician, but also for the patient. While the physician uses the ultrasound data for diagnostic purposes the patient might be more interested in beautiful images in the case of prenatal imaging. Ultrasound data is noisy by nature and visually compelling 3D renderings are not always trivial to produce. This paper presents a technique which enables extraction of a smooth surface mesh from the ultrasound data by combining previous research in ultrasound processing with research in point cloud surface reconstruction. After filtering the ultrasound data using Variational Classification we extract a set of surface points. This set of points is then used to train an Adaptive Compactly Supported Radial Basis Functions system, a technique for surface reconstruction of noisy laser scan data. The resulting technique can be used to extract surfaces with adjustable smoothness and resolution and has been tested on various ultrasound datasets.

We propose an approach for verification of volume rendering correctness based on an analysis of the volume rendering integral, the basis of most DVR algorithms. With respect to the most common discretization of this continuous model (Riemann summation), we make assumptions about the impact of parameter changes on the rendered results and derive convergence curves describing the expected behavior. Specifically, we progressively refine the number of samples along the ray, the grid size, and the pixel size, and evaluate how the errors observed during refinement compare against the expected approximation errors. We derive the theoretical foundations of our verification approach, explain how to realize it in practice, and discuss its limitations. We also report the errors identified by our approach when applied to two publicly available volume rendering packages.

Molecular visualization is often challenged with rendering of large molecular structures in real time. We introduce a novel approach that enables us to show even large protein complexes. Our method is based on the level-of-detail concept, where we exploit three different abstractions combined in one visualization. Firstly, molecular surface abstraction exploits three different surfaces, solvent-excluded surface (SES), Gaussian kernels and van der Waals spheres, combined as one surface by linear interpolation. Secondly, we introduce three shading abstraction levels and a method for creating seamless transitions between these representations. The SES representation with full shading and added contours stands in focus while on the other side a sphere representation of a cluster of atoms with constant shading and without contours provide the context. Thirdly, we propose a hierarchical abstraction based on a set of clusters formed on molecular atoms. All three abstraction models are driven by one importance function classifying the scene into the near-, mid- and far-field. Moreover, we introduce a methodology to render the entire molecule directly using the A-buffer technique, which further improves the performance. The rendering performance is evaluated on series of molecules of varying atom counts., Funding Agencies|PhysioIllustration research project - Norwegian Research Council [218023]; Vienna Science and Technology Fund (WWTF) [VRG11-010]; EC Marie Curie Career Integration Grant [PCIG13-GA-2013-618680]; Excellence Center at Linkoping and Lund in Information Technology (ELLIIT); Swedish Research Council through the Linnaeus Center for Control, Autonomy, and Decisionmaking in Complex Systems (CADICS); Swedish e-Science Research Centre (SeRC); VR [2011-4113]

Radiology is one of themain tools inmodernmedicine.Anumerous set of deceases, ailments and treatments utilize accurate images of the patient. Ultrasound is one of the most frequently used imaging modality in medicine. The high spatial resolution, its interactive nature and non-invasivenessmakes it the first choice inmany examinations. Image interpretation is one of ultrasound’s main challenges. Much training is required to obtain a confident skill level in ultrasound-based diagnostics. State-of-the-art graphics techniques is needed to providemeaningful visualizations of ultrasound in real-time. In this paper we present the process-pipeline for ultrasound visualization, including an overview of the tasks performed in the specific steps. To provide an insight into the trends of ultrasound visualization research, we have selected a set of significant publications and divided them into a technique-based taxonomy covering the topics pre-processing, segmentation, registration, rendering and augmented reality. For the different technique types we discuss the difference between ultrasound-based techniques and techniques for other modalities.

We present a visualization system for incident commanders in urban search and rescue scenarios that supports the inspection and access path planning in post-disaster structures. Utilizing point cloud data acquired from unmanned robots, the system allows for assessment of automatically generated paths, whose computation is based on varying risk factors, in an interactive 3D environment increasing immersion. The incident commander interactively annotates and reevaluates the acquired point cloud based on live feedback. We describe design considerations, technical realization, and discuss the results of an expert evaluation that we conducted to assess our system.

Deep Brain Stimulation (DBS) is a surgical intervention that is known to reduce or eliminate the symptoms of common movement disorders, such as Parkinson.s disease, dystonia, or tremor. During the intervention the surgeon places electrodes inside of the patient.s brain to stimulate speci.c regions. Since these regions span only a couple of millimeters, and electrode misplacement has severe consequences, reliable and accurate navigation is of great importance. Usually the surgeon relies on fused CT and MRI data sets, as well as direct feedback from the patient. More recently Microelectrode Recordings (MER), which support navigation by measuring the electric .eld of the patient.s brain, are also used. We propose a visualization system that fuses the different modalities: imaging data, MER and patient checks, as well as the related uncertainties, in an intuitive way to present placement-related information in a consistent view with the goal of supporting the surgeon in the .nal placement of the stimulating electrode. We will describe the design considerations for our system, the technical realization, present the outcome of the proposed system, and provide an evaluation.

SIGRAD 2013 We are happy to announce the 12th SIGRAD Conference Proceedings. SIGRAD 2013 will be held in Norrköping, Sweden, on June 13 and 14, 2013. SIGRAD 2013 focuses on visual computing, and solicits the submission of original research papers that advance the state-ofthe-art of one of the subareas of visual computing, ranging from computer graphics and visualization to human-computer-interaction. SIGRAD 2013 is the premier Nordic forum for computer graphics and visualization advances for academia, and industry. This annual event brings together researchers and practitioners with interest in techniques, tools, and technology from various fields such as computer graphics,visualization, visual analytics, or human-computer interaction. Each paper in this conference proceedings was peerreviewed by at least three reviewers from the international program committee consisting of 26 experts listed below. Based on this set of reviews, the conference co-chairs accepted 9 papers in total and compiled the final program. Jonas Unger and Timo Ropinski

Multiple sequence alignment (MSA) is essential as an initial step in studying molecular phylogeny as well as during the identification of genomic rearrangements. Recent advances in sequencing techniques have led to a tremendous increase in the number of sequences to be analyzed. As a result, a greater demand is being placed on visualization techniques, as they have the potential to reveal the underlying information in large-scale MSAs. In this work, we present a novel visualization technique for conveying the patterns in large-scale MSAs. By applying gradient vector flow analysis to the MSA data, we can extract and visually emphasize conservations and other patterns that are relevant during the MSA exploration process. In contrast to the traditional visual representation of MSAs, which exploits color-coded tables, the proposed visual metaphor allows us to provide an overview of large MSAs as well as to highlight global patterns, outliers, and data distributions. We will motivate and describe the proposed algorithm, and further demonstrate its application to large-scale MSAs.

In this paper, we study and analyze seven state-of-the-art volumetric illumination methods, in order to determine their differences with respect to the underlying theoretical mathematical models and numerical problems potentially arising during implementation. The chosen models are half angle slicing, directional occlusion shading, multidirectional occlusion shading, shadow volume propagation, spherical harmonic lighting, dynamic ambient occlusion and progressive photon mapping. We put these models into a unified mathematical framework, which allows them to be compared among each other as well as to the global volume rendering equation. We will discuss the mathematical differences of the compared models and describe the numerical implications of the simplifications made by each method, CADICS, CMIV

Diffusion Tensor Imaging (DTI) in combination with fiber tracking algorithms enables visualization and characterization of white matter structures in the brain. However, the low spatial resolution associated with the inherently low signal-to-noise ratio of DTI has raised concerns regarding the reliability of the obtained fiber bundles. Therefore, recent advancements in fiber tracking algorithms address the accuracy of the reconstructed fibers. In this paper, we propose a novel approach for analyzing and reducing the uncertainty of densely sampled 3D DTI fibers in biological specimens. To achieve this goal, we derive the uncertainty in the reconstructed fiber tracts using different deterministic and stochastic fiber tracking algorithms. Through a unified representation of the derived uncertainty, we generate a new set of reconstructed fiber tracts that has a lower level of uncertainty. We will discuss our approach in detail and present the results we could achieve when applying it to several use cases.

Direct Volume Rendering of Finite Element models is challengingsince the visualisation process is performed in worldcoordinates, whereas data fields are usually defined overthe elements’ material coordinate system. In this paper wepresent a framework for Direct Volume Rendering of FiniteElement models. We present several novel implementationsvisualising Finite Element data directly without requiring resamplinginto world coordinates. We evaluate the methodsusing several biomedical Finite Element models. Our GPUimplementation of ray-casting in material coordinates usingdepth peeling is several orders of magnitude faster than thecorresponding CPU approach, and our new ray interpolationapproach achieves near interactive frame rates for high-orderfinite element models at high resolutions.

In this paper, we enable interactive volumetric global illumination by extending photon mapping techniques to handle interactive transfer function (TF) and material editing in the context of volume rendering. We propose novel algorithms and data structures for finding and evaluating parts of a scene affected by these parameter changes, and thus support efficient updates of the photon map. In direct volume rendering (DVR) the ability to explore volume data using parameter changes, such as editable TFs, is of key importance. Advanced global illumination techniques are in most cases computationally too expensive, as they prevent the desired interactivity. Our technique decreases the amount of computation caused by parameter changes, by introducing Historygrams which allow us to efficiently reuse previously computed photon media interactions. Along the viewing rays, we utilize properties of the light transport equations to subdivide a view-ray into segments and independently update them when invalid. Unlike segments of a view-ray, photon scattering events within the volumetric medium needs to be sequentially updated. Using our Historygram approach, we can identify the first invalid photon interaction caused by a property change, and thus reuse all valid photon interactions. Combining these two novel concepts, supports interactive editing of parameters when using volumetric photon mapping in the context of DVR. As a consequence, we can handle arbitrarily shaped and positioned light sources, arbitrary phase functions, bidirectional reflectance distribution functions and multiple scattering which has previously not been possible in interactive DVR., Funding Agencies|Excellence Center at Linkoping and Lund in Information Technology (ELLIIT)||Swedish e-Science Research Centre (SeRC), CADICS, CMIV

Ultrasound is one of the most frequently used imaging modality in medicine. The high spatial resolution, its interactive nature and non-invasiveness makes it the first choice in many examinations. Image interpretation is one of ultrasound's main challenges. Much training is required to obtain a confident skill level in ultrasound-based diagnostics. State-of-the-art graphics techniques is needed to provide meaningful visualizations of ultrasound in real-time. In this paper we present the process-pipeline for ultrasound visualization, including an overview of the tasks performed in the specific steps. To provide an insight into the trends of ultrasound visualization research, we have selected a set of significant publications and divided them into a technique-based taxonomy covering the topics pre-processing, segmentation, registration, rendering and augmented reality. For the different technique types we discuss the difference between ultrasound-based techniques and techniques for other modalities.

This book contains the papers presented at the Eurographics Workshop on Visual Computing for Biology and Medicine 2012, organized by the Eurographics Association, which took place in Noroping, Sweden, on September 27-28, 2012.

In this paper, we describe a novel approach for applying texture mapping to volumetric data sets. In contrast to previous approaches, the presented technique enables a unified integration of 2D and 3D textures and thus allows to emphasize material boundaries as well as volumetric regions within a volumetric data set at the same time. One key contribution of this paper is a parametrization technique for volumetric data sets, which takes into account material boundaries and volumetric regions. Using this technique, the resulting parametrizations of volumetric data sets enable texturing effects which create a higher degree of realism in volume rendered images. We evaluate the quality of the parametrization and demonstrate the usefulness of the proposed concepts by combining volumetric texturing with volumetric lighting models to generate photorealistic volume renderings. Furthermore, we show the applicability in the area of illustrative visualization., Funding Agencies|Deutsche Forschungsgemeinschaft (DFG)||ELLIIT||Strategic Area for ICT research||Swedish Government||ViMaL project (FWF)|P21695||SFB 656 MoBil

A major challenge when designing general purpose graphics hardware is to allow efficient access to texture data. Although different rendering paradigms vary with respect to their data access patterns, there is no flexibility when it comes to data caching provided by the graphics architecture. In this paper we focus on volume ray-casting, and show the benefits of algorithm-aware data caching. Our Marching Caches method exploits inter-ray coherence and thus utilizes the memory layout of the highly parallel processors by allowing them to share data througha cache which marches along with the ray front. By exploiting Marching Caches we can apply higher-order reconstruction and enhancement filters to generate more accurate and enriched renderings with an improved rendering performance. We have tested our Marching Caches with seven different filters, e. g., Catmul-Rom, B-spline, ambient occlusion projection, and could show that a speed up of four times can be achieved compared to using the caching implicitly provided by the graphics hardware, and that the memory bandwidth to global memory can be reduced by orders of magnitude. Throughout the paper, we will introduce the Marching Cache concept, provide implementation details and discuss the performance and memory bandwidth impact when using different filters., CADICS, CMIV

Interactive volume rendering in its standard formulation has become an increasingly important tool in many application domains. In recent years several advanced volumetric illumination techniques to be used in interactive scenarios have been proposed. These techniques claim to have perceptual benefits as well as being capable of producing more realistic volume rendered images. Naturally, they cover a wide spectrum of illumination effects, including varying shadowing and scattering effects. In this article, we review and classify the existing techniques for advanced volumetric illumination. The classification will be conducted based on their technical realization, their performance behavior as well as their perceptual capabilities. Based on the limitations revealed in this review, we will define future challenges in the area of interactive advanced volumetric illumination., CADICS, CMIV

Finite element (FE) models are frequently used in engineering and life sciences within time-consuming simulations. In contrast with the regular grid structure facilitated by volumetric data sets, as used in medicine or geosciences, FE models are defined over a non-uniform grid. Elements can have curved faces and their interior can be defined through high-order basis functions, which pose additional challenges when visualizing these models. During ray-casting, the uniformly distributed sample points along each viewing ray must be transformed into the material space defined within each element. The computational complexity of this transformation makes a straightforward approach inadequate for interactive data exploration. In this paper, we introduce a novel coherency-based method which supports the interactive exploration of FE models by decoupling the expensive world-to-material space transformation from the rendering stage, thereby allowing it to be performed within a precomputation stage. Therefore, our approach computes view-independent proxy rays in material space, which are clustered to facilitate data reduction. During rendering, these proxy rays are accessed, and it becomes possible to visually analyze high-order FE models at interactive frame rates, even when they are time-varying or consist of multiple modalities. Within this paper, we provide the necessary background about the FE data, describe our decoupling method, and introduce our interactive rendering algorithm. Furthermore, we provide visual results and analyze the error introduced by the presented approach., Funding Agencies|Swedish Research Council (VR)|2011-4113|Excellence Center at Linkoping and Lund in Information Technology (ELLIIT)||Swedish e-Science Research Centre (SeRC)