arXiv subjects

João Madeiras Pereira

Publications and source records attributed to João Madeiras Pereira.

10 recordsLinked to original sources

arXiv2024

Benchmarking Instance-Centric Counterfactual Algorithms for XAI: From White Box to Black Box

This study investigates the impact of machine learning models on the generation of counterfactual explanations by conducting a benchmark evaluation over three different types of models: a decision tree (fully transparent, interpretable, white-box model), a random forest (semi-interpretable, grey-box model), and a neural network (fully opaque, black-box model). We tested the counterfactual generation process using four algorithms (DiCE, WatcherCF, prototype, and GrowingSpheresCF) in the literature in 25 different datasets. Our findings indicate that: (1) Different machine learning models have little impact on the generation of counterfactual explanations; (2) Counterfactual algorithms based uniquely on proximity loss functions are not actionable and will not provide meaningful explanations; (3) One cannot have meaningful evaluation results without guaranteeing plausibility in the counterfactual generation. Algorithms that do not consider plausibility in their internal mechanisms will lead to biased and unreliable conclusions if evaluated with the current state-of-the-art metrics; (4) A counterfactual inspection analysis is strongly recommended to ensure a robust examination of counterfactual explanations and the potential identification of biases.

cs.LG↗

arXiv2024

Eery Space: Facilitating Virtual Meetings Through Remote Proxemics

Virtual meetings have become increasingly common with modern video-conference and collaborative software. While they allow obvious savings in time and resources, current technologies add unproductive layers of protocol to the flow of communication between participants, rendering the interactions far from seamless. In this work we introduce Remote Proxemics, an extension of proxemics aimed at bringing the syntax of co-located proximal interactions to virtual meetings. We propose Eery Space, a shared virtual locus that results from merging multiple remote areas, where meeting participants' are located side-by-side as if they shared the same physical location. Eery Space promotes collaborative content creation and seamless mediation of communication channels based on virtual proximity. Results from user evaluation suggest that our approach is effective at enhancing mutual awareness between participants and sufficient to initiate proximal exchanges regardless of their geolocation, while promoting smooth interactions between local and remote people alike. These results happen even in the absence of visual avatars and other social devices such as eye contact, which are largely the focus of previous approaches.

cs.HC↗

arXiv2024

Effects of Realism and Representation on Self-Embodied Avatars in Immersive Virtual Environments

Virtual Reality (VR) has recently gained traction with many new and ever more affordable devices being released. The increase in popularity of this paradigm of interaction has given birth to new applications and has attracted casual consumers to experience VR. Providing a self-embodied representation (avatar) of users' full bodies inside shared virtual spaces can improve the VR experience and make it more engaging to both new and experienced users . This is especially important in fully immersive systems, where the equipment completely occludes the real world making self awareness problematic. Indeed, the feeling of presence of the user is highly influenced by their virtual representations, even though small flaws could lead to uncanny valley side-effects. Following previous research, we would like to assess whether using a third-person perspective could also benefit the VR experience, via an improved spatial awareness of the user's virtual surroundings. In this paper we investigate realism and perspective of self-embodied representation in VR setups in natural tasks, such as walking and avoiding obstacles. We compare both First and Third-Person perspectives with three different levels of realism in avatar representation. These range from a stylized abstract avatar, to a "realistic" mesh-based humanoid representation and a point-cloud rendering. The latter uses data captured via depth-sensors and mapped into a virtual self inside the Virtual Environment. We present a throughout evaluation and comparison of these different representations, describing a series of guidelines for self-embodied VR applications. The effects of the uncanny valley are also discussed in the context of navigation and reflex-based tasks.

cs.HC↗

arXiv2024

Fluid Implicit Particle Simulation for CPU and GPU

One of the current challenges in physically-based simulations, and, more specifically, fluid simulations, is to produce visually appealing results at interactive rates, capable of being used in multiple forms of media. In recent times, a lot of effort has been made with regards to this with the use of multi-core architectures, as many of the computations involved in the algorithms for these simulations are very well suited for these architectures. Although there is a considerable amount of works regarding acceleration techniques in this field, there is yet room to further explore and analyze some of them. To investigate this problem, we surveyed the topic of fluid simulations and some of the recent contributions towards this field. Additionally, we implemented two versions of a fluid simulation algorithm, one on the CPU and the other on the GPU using NVIDIA's CUDA framework, with the intent of gaining a better understanding of the effort needed to move these simulations to a multi-core architecture and the performance gains that we get with it.

cs.GR↗

arXiv2023

Video-Based Rendering Techniques: A Survey

Three-dimensional reconstruction of events recorded on images has been a common challenge between computer vision and computer graphics for a long time. Estimating the real position of objects and surfaces using vision as an input is no trivial task and has been approached in several different ways. Although huge progress has been made so far, there are several open issues to which an answer is needed. The use of videos as an input for a rendering process (video-based rendering, VBR) is something that recently has been started to be looked upon and has added many other challenges and also solutions to the classical image-based rendering issue (IBR). This article presents the state of art on video-based rendering and image-based techniques that can be applied on this scenario, evaluating the open issues yet to be solved, indicating where future work should be focused.

cs.CV↗

arXiv2023

Beyond the Screen: Reshaping the Workplace with Virtual and Augmented Reality

Although extended reality technologies have enjoyed an explosion in popularity in recent years, few applications are effectively used outside the entertainment or academic contexts. This work consists of a literature review regarding the effective integration of such technologies in the workplace. It aims to provide an updated view of how they are being used in that context. First, we examine existing research concerning virtual, augmented, and mixed-reality applications. We also analyze which have made their way to the workflows of companies and institutions. Furthermore, we circumscribe the aspects of extended reality technologies that determined this applicability.

cs.HC↗

arXiv2023

Visualizing Plasma Physics Simulations in Immersive Environments

Plasma physics simulations create complex datasets for which researchers need state-of-the-art visualization tools to gain insights. These datasets are 3D in nature but are commonly depicted and analyzed using 2D idioms displayed on 2D screens. These offer limited understandability in a domain where spatial awareness is key. Virtual reality (VR) can be used as an alternative to conventional means for analyzing such datasets. VR has been known to improve depth and spatial relationship perception, which are fundamental for obtaining insights into 3D plasma morphology. Likewise, VR can potentially increase user engagement by offering more immersive and enjoyable experiences. Methods This study presents PlasmaVR, a proof-of-concept VR tool for visualizing datasets resulting from plasma physics simulations. It enables immersive multidimensional data visualization of particles, scalar, and vector fields and uses a more natural interface. The study includes user evaluation with domain experts where PlasmaVR was employed to assess the possible benefits of immersive environments in plasma physics visualization. The experimental group comprised five plasma physics researchers who were asked to perform tasks designed to represent their typical analysis workflow. To assess the suitability of the prototype for the different types of tasks, a set of objective metrics, such as completion time and number of errors, were measured. The prototype's usability was also evaluated using a standard System Usability Survey questionnaire.

cs.GR↗

arXiv2023

Survey of Rigid Body Simulation with Extended Position Based Dynamics

Interactive real-time rigid body simulation is a crucial tool in any modern game engine or 3D authoring tool. The quest for fast, robust and accurate simulations is ever evolving. PBRBD (Position Based Rigid Body Dynamics), a recent expansion of PBD (Position Based Dynamics), is a novel approach for this issue. This work aims at providing a comprehensible state-of-the art comparison between Position Based methods and other real-time simulation methods used for rigid body dynamics using a custom 3D physics engine for benchmarking and comparing PBRBD (Position Based Rigid Body Dynamics), and some variants, with state-of-the-art simulators commonly used in the gaming industry, PhysX and Havok. Showing that PBRBD can produce simulations that are accurate and stable, excelling at maintaining stable energy levels, and allowing for a variety of constraints, but is limited in its handling of stable stacks of rigid bodies.

cs.GR↗

arXiv2022

Improving X-ray Diagnostics through Eye-Tracking and XR

There is a growing need to assist radiologists in performing X-ray readings and diagnoses fast, comfortably, and effectively. As radiologists strive to maximize productivity, it is essential to consider the impact of reading rooms in interpreting complex examinations and ensure that higher volume and reporting speeds do not compromise patient outcomes. Virtual Reality (VR) is a disruptive technology for clinical practice in assessing X-ray images. We argue that conjugating eye-tracking with VR devices and Machine Learning may overcome obstacles posed by inadequate ergonomic postures and poor room conditions that often cause erroneous diagnostics when professionals examine digital images.

cs.HC↗

arXiv2022

Design requirements to improve laparoscopy via XR

Laparoscopic surgery has the advantage of avoiding large open incisions and thereby decreasing blood loss, pain, and discomfort to patients. However, on the other side, it is hampered by restricted workspace, ambiguous communication, and surgeon fatigue caused by non-ergonomic head positioning. We aimed to identify critical problems and suggest design requirements and solutions. We used user and task analysis methods to learn about practices performed in an operating room by observing surgeons in their working environment to understand how they performed tasks and achieved their intended goals. Drawing on observations and analysis from recorded laparoscopic surgeries, we have identified several constraints and design requirements to propose potential solutions to address the issues. Surgeons operate in a dimly lit environment, surrounded by monitors, and communicate through verbal commands and pointing gestures. Therefore, performing user and task analysis allowed us to better understand the existing problems in laparoscopy while identifying several communication constraints and design requirements, which a solution has to follow to address those problems. Our contributions include identifying design requirements for laparoscopy surgery through a user and task analysis. These requirements propose design solutions towards improved surgeons' comfort and make the surgical procedure less laborious.

cs.HC↗