Samuel S. Silva

Head-mounted display versus desktop for 3D navigation in virtual reality: a user study

Virtual Reality (VR) has been constantly evolving since its early days, and is now a fundamental technology in different application areas. User evaluation is a crucial step in the design and development of VR systems that do respond to users’ needs, as well as for identifying applications that indeed gain from the use of such technology. Yet, there is not much work reported concerning usability evaluation and validation of VR systems, when compared with the traditional desktop setup. The paper presents a user study performed, as a first step, for the evaluation of a low-cost VR system using a Head-Mounted Display (HMD). That system was compared to a traditional desktop setup through an experiment that assessed user performance, when carrying out navigation tasks in a game scenario for a short period. The results show that, although users were generally satisfied with the VR system, and found the HMD interaction intuitive and natural, most performed better with the desktop setup.

Technical Section: Using color in visualization: A survey

Color mapping is an important technique used in visualization to build visual representations of data and information. With output devices such as computer displays providing a large number of colors, developers sometimes tend to build their visualization to be visually appealing, while forgetting the main goal of clear depiction of the underlying data. Visualization researchers have profited from findings in adjoining areas such as human vision and psychophysics which, combined with their own experience, enabled them to establish guidelines that might help practitioners to select appropriate color scales and adjust the associated color maps, for particular applications. This survey presents an overview on the subject of color scales by focusing on important guidelines, experimental research work and tools proposed to help non-expert users.

There is More to Color Scales than Meets the Eye: A Review on the Use of Color in Visualization

The appropriate use of color in Visualization is a very important subject. The choice of the proper color scale to use with a particular data set is not just a matter of choosing the prettiest representation. Throughout the years researchers have studied this subject and managed to propose guidelines which help users along the process of color scale selection. This article presents a brief overview on the subject focusing on the desired properties for color scales, the guidelines that should drive their choice, the advantages of applying those guidelines, the experimental research work on the field, and the tools proposed to help non-expert users.

Elderly Centered Design for Interaction – The Case of the S4S Medication Assistant☆

Abstract Several aspects of older adults’ life can benefit from recent technological developments, but success in harnessing this potential depends on careful design and accessible, easy to use products. Design and development must be centered on the elderly and adequately consider interaction. In this paper we follow this design approach and put it to the test in developing a concrete application, aimed to contribute to lower the high levels of non-adherence to medication in the elderly population. The “Medication Assistant” application was developed following an iterative method centered, from the start, on the elderly and interaction design. The method repeats short-time development cycles integrating definition of scenarios and goals, requirements engineering, design, prototyping and evaluation. Evaluation, by end-users, of the increasingly refined prototypes, is a key characteristic of the method. The evaluation results provide information related to strengths and weaknesses of the application and yield suggestions regarding changes and improvements, valuable support further development. Results regarding evaluation of the second prototype of “Medication Assistant” are presented.

PolyMeCo - a polygonal mesh comparison tool

Polygonal meshes are used in many areas to model different objects and structures. Depending on their applications, they sometimes have to be processed to, for instance, reduce their complexity (simplification). This mesh processing introduces error, whose evaluation is important when choosing the kind of processing that is to be done for a particular application. Although some mesh comparison tools are described in the literature, little attention has been given to the way results are presented. A tool is presented which enhances the way users perform mesh analysis and comparison, by providing an environment where several visualization options are available and can be used in a coordinated way.

Design and Development of Speech Interaction: A Methodology

Using speech in computer interaction is advantageous in many situation and more natural for the user. However, development of speech enabled applications presents, in general, a big challenge when designing the application, regarding the implementation of speech modalities and what the speech recognizer will understand.

A 3d tool for left ventricle segmentation editing

Image segmentation has a very important role in many application areas, such as medical imaging. Even robust segmentation methods cannot deal with the wide range of variation observed, for example, in shape and orientation of an anatomical structure. Given the need to accomplish accurate segmentations in order to perform quantitative measurements or compare structures in different time instances, it is important to have tools which allow easy segmentation editing/correction by experts. In 3D images (e.g., obtained using CT scanners) performing segmentation editing of regions which span several slices might be a tiresome task if it has to be done slice-by-slice with a 2D tool. This article presents a 3D segmentation editing tool, to be applied to left ventricle segmentations, which enables radiographers to correct segmentations provided by an automatic method.

Education: PolyMeCo-An integrated environment for polygonal mesh analysis and comparison

Polygonal meshes are used in several application areas to model different objects and structures. Depending on the application, mesh models sometimes have to be processed to, for instance, reduce their complexity (mesh simplification). Such operations introduce differences regarding the original mesh, whose evaluation is of paramount importance when choosing the processing methods to be applied for a particular purpose. Although some mesh analysis and comparison tools are described in the literature, little attention has been given to the way mesh features and mesh comparison results can be visualized. Moreover, particular functionalities have to be made available to enable systematic use and proper data analysis and exploration. PolyMeCo-a tool for polygonal mesh analysis and comparison-was designed and developed taking the above objectives into account. It enhances the way users analyze features and compare meshes by providing an integrated environment where various mesh quality measures and several visualization options are available and can be used in a coordinated way, thus leading to greater insight into the visualized data.

Comparison of Methods for the Simplification of Mesh Models using Quality Indices and an Observer Study

The complexity of a polygonal mesh model is usually reduced by applying a simplification method, resulting in a similar mesh having less vertices and faces. Although several such methods have been developed, only a few observer studies are reported comparing them regarding the perceived quality of the obtained simplified meshes, and it is not yet clear how the choice of a given method, and the level of simplification achieved, influence the quality of the resulting model, as perceived by the final users. Mesh quality indices are the obvious less costly alternative to user studies, but it is also not clear how they relate to perceived quality, and which indices best describe the users behavior. Following on earlier work carried out by the authors, but only for mesh models of the lungs, a comparison among the results of three simplification methods was performed through (1) quality indices and (2) a controlled experiment involving 65 observers, for a set of five reference mesh models of different kinds. These were simplified using two methods provided by the OpenMesh library - one using error quadrics, the other additionally using a normal flipping criterion - and also by the widely used QSlim method, for two simplification levels: 50% and 20% of the original number of faces. The main goal was to ascertain whether the findings previously obtained for lung models, through quality indices and a study with 32 observers, could be generalized to other types of models and confirmed for a larger number of observers. Data obtained using the quality indices and the results of the controlled experiment were compared and do confirm that some quality indices (e.g., geometric distance and normal deviation, as well as a new proposed weighted index) can be used, in specific circumstances, as reasonable estimators of the user perceived quality of mesh models.

Unsupervised segmentation of the vocal tract from real-time MRI sequences

HighlightsVocal tract segmentation considering sequential nature of the RT-MRI data.Explicit consideration of vocal tract configurations with an open and closed velum.Single, high level segmentation initialisation per speaker, unsupervised operation thereafter.Small set of images for training: small manual annotation overhead.Evaluation of precision and accuracy over large image set and considering annotated images by four observers. Advances on real-time magnetic resonance imaging (RT-MRI) make it suitable to study the dynamic aspects of the upper airway. One of the main challenges concerns how to deal with the large amount of data resulting from these studies, particularly to extract relevant features for analysis such as the vocal tract profiles. A method is proposed, based on a modified active appearance model (AAM) approach, for unsupervised segmentation of the vocal tract from midsagittal RT-MRI sequences. The described approach was designed considering the low inter-frame difference. As a result, when compared to a traditional AAM approach, segmentation is performed faster and model convergence is improved, attaining good results using small training sets. The main goal is to extract the vocal tract profiles automatically, over time, providing identification of different regions of interest, to allow the study of the dynamic features of the vocal tract, for example, during speech production. The proposed method has been evaluated against vocal tract delineations manually performed by four observers, yielding good agreement.