First-person locomotion in 3D virtual environments: a usability analysis

3D Virtual Environments (VE) are becoming popular as a tool for cognitive, functional and psychological assessment. Navigation in these environments is recognized as one of the most difficult activities in 3D Virtual Environments (VE). Users unfamiliar to 3D games, specially elder persons, get puzzled when they try to virtually move an avatar through these environments. Their inability to navigate prevents them from concentrating in the task and even to finish it. In this paper, we analyze the influence of different factors in locomotion control. We investigate the impact of having the cursor fixed at the camera center or leaving it free inside the current view. We also analyze the influence of the pitch angle on the camera control. In addition, we have designed an automatic locomotion system that we compare to user-controlled locomotion. We describe a virtual scenario and a test task that we have implemented to evaluate these different methods with users of diverse profiles.Postprint (published version

Hardware and software improvements of volume splatting

This paper proposes different hardware-based acceleration of the three classical splatting strategies: emph{composite-every-sample}, emph{object-space sheet-buffer} and emph{image-space sheet-buffer}.Preprin

Frame-to-frame coherent image-aligned sheet-buffered splatting

Splatting is a classical volume rendering technique that has recently gained in popularity for the visualization of point-based suface models. Up to now, there has been few publications on its adaptation to time-varying data. In this paper, we propose a novel frame-to-frame coherent view-aligned sheet-buffer splatting of time-varying data, that tries to reduce as much as possible the memory load and the rendering computations taking into account the similarity in the data and in the images at successive instants of time. The results presented in the paper are encouraging and show that the proposed technique may be useful to explore data through time.Postprint (published version

An Adaptive Cutaway with Volume Context Preservation

Knowledge expressiveness of scientific data is one of the most important visualization goals. However, current volume visualization systems require a lot of expertise from the final user. In this paper, we present a GPU-based ray casting interactive framework that computes two initial complementary camera locations and allows to select the focus interactively, on interesting structures keeping the volume’s context information with an adaptive cutaway technique. The adaptive cutaway surrounds the focused structure while preserving a depth immersive impression in the data set. Finally, we present a new brush widget to edit interactively the opening of the cutaway and to graduate the context in the final image.Peer ReviewedPostprint (published version

Image-space sheet-buffered splatting on the GPU

Image-Space Sheet-Buffered Splatting is a popular high quality volume-rendering technique specially suitable for zoomed views of the data. On the contrary to other splatting approaches, it processes the voxels in slabs perpendicular to the viewing direction. Recently, a GPU design of this method has been proposed that considerably accelerates the rendering stage. However, the bottleneck of the method is the computation of the buckets, i.e the structure handling the voxels to be rendered in each slab. This stage of the method is done on the CPU. In this paper, we propose a new design of the method that creates and manages the buckets on the GPU. The proposed method is more than twice faster than the previous ones.Postprint (published version

Efficient complementary viewpoint selection in volume rendering

A major goal of visualization is to appropriately express knowledge of scientific data. Generally, gathering visual information contained in the volume data often requires a lot of expertise from the final user to setup the parameters of the visualization. One way of alleviating this problem is to provide the position of inner structures with different viewpoint locations to enhance the perception and construction of the mental image. To this end, traditional illustrations use two or three different views of the regions of interest. Similarly, with the aim of assisting the users to easily place a good viewpoint location, this paper proposes an automatic and interactive method that locates different complementary viewpoints from a reference camera in volume datasets. Specifically, the proposed method combines the quantity of information each camera provides for each structure and the shape similarity of the projections of the remaining viewpoints based on Dynamic Time Warping. The selected complementary viewpoints allow a better understanding of the focused structure in several applications. Thus, the user interactively receives feedback based on several viewpoints that helps him to understand the visual information. A live-user evaluation on different data sets show a good convergence to useful complementary viewpoints.Postprint (published version

3D pore analysis of sedimentary rocks

A 3D representation of the internal structure and fabric of sedimentary rocks is of paramount interest to evaluate their structural parameters such as porosity, pore-size distribution and permeability. The classical experimental technique to evaluate the pore space volume and pore size distribution is the Mercury Intrusion Porosimetry (MIP). Computer-based methods use 3D imaging technologies such as Computer Tomography (CT) scanned images to construct and evaluate a 3D virtual representation of the internal pore distribution. In this work, based on a three samples set of sandstone, we apply two numerical (computer-based) methods in order to reconstruct and analyse the internal pore network, and compare it with the results obtained by MIP analysis. The first numerical method performs a virtual simulation of MIP. The second one obtains a graph of pores using a sphere-filling based approach. For all methods, we compute the global porosity and the pore-size distribution. Moreover, with the numerical methods, we obtain the total porosity and a graph representing the pore space that can be visualized with 3D illustration techniques.Postprint (published version

Virtual porosimeter

Recently, the term BioCAD has appeared to refer to the modeling of biological processes. This work focuses on the analysis of structural properties such as porosity of bioimplants for bone reconstruction. Specifically, we present a method that, using 3D microCT images, simulates the behavior of a porosimeter, i.e. an instrument to measure the porous structure of samples. After segmentation, we apply a process, based on connected component labeling and skeleton computation, which produces a result comparable to the real porosimeter experiment.Postprint (published version

Time-varying volume visualization

Volume rendering is a very active research field in Computer Graphics because of its wide range of applications in various sciences, from medicine to flow mechanics. In this report, we survey a state-of-the-art on time-varying volume rendering. We state several basic concepts and then we establish several criteria to classify the studied works: IVR versus DVR, 4D versus 3D+time, compression techniques, involved architectures, use of parallelism and image-space versus object-space coherence. We also address other related problems as transfer functions and 2D cross-sections computation of time-varying volume data. All the papers reviewed are classified into several tables based on the mentioned classification and, finally, several conclusions are presented.Preprin

Multiancestry analysis of the HLA locus in Alzheimer’s and Parkinson’s diseases uncovers a shared adaptive immune response mediated by HLA-DRB1*04 subtypes

Across multiancestry groups, we analyzed Human Leukocyte Antigen (HLA) associations in over 176,000 individuals with Parkinson’s disease (PD) and Alzheimer’s disease (AD) versus controls. We demonstrate that the two diseases share the same protective association at the HLA locus. HLA-specific fine-mapping showed that hierarchical protective effects of HLA-DRB1*04 subtypes best accounted for the association, strongest with HLA-DRB1*04:04 and HLA-DRB1*04:07, and intermediary with HLA-DRB1*04:01 and HLA-DRB1*04:03. The same signal was associated with decreased neurofibrillary tangles in postmortem brains and was associated with reduced tau levels in cerebrospinal fluid and to a lower extent with increased Aβ42. Protective HLA-DRB1*04 subtypes strongly bound the aggregation-prone tau PHF6 sequence, however only when acetylated at a lysine (K311), a common posttranslational modification central to tau aggregation. An HLA-DRB1*04-mediated adaptive immune response decreases PD and AD risks, potentially by acting against tau, offering the possibility of therapeutic avenues