Alfredo Ferreira

• PhD in Computer Science
• Professor (Associate) at University of Lisbon

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 P...

Three-dimensional immersive sketching for content creation and modeling has been studied for some time. However, research in this domain mainly focused on CAVE-like scenarios. These setups can be expensive and offer a narrow interaction space. Building more affordable setups using head-mounted displays is possible, allowing greater immersion and a...

Dam safety control is a multifaceted activity that requires analysis, monitoring, and structural behavior prediction. It entails interpreting vast amounts of data from sensor networks integrated into dam structures. The application of extended reality technologies for situated immersive analysis allows data to be contextualized directly over the ph...

Ray tracing is a computer graphics technique used to produce realistic visuals by physically simulating the behavior of light. Although this technique can be described straightforwardly, fully comprehending it might be challenging. It is typically taught in the classroom using two-dimensional formats like paper or a blackboard. We propose using imm...

This article presents a survey on extended reality (XR) application to architecture, engineering, and construction (AEC). A systematic literature review (SLR) of studies found in the Scopus digital library is carried out for that purpose. The SLR comprises 983 relevant papers published between 2011 and 2022. It frames and aggregates research by the...

Dam Safety Control has been at the front line of technology adoption in what concerns data acquisition. However, it does not take full advantage of the latest advancements when it comes to in-situ, real-time, information visualization. This work explores the application of Augmented Reality to the inspection and monitoring of large Civil Engineerin...

Sketching is a natural and intuitive communication tool used for expressing concepts or ideas which are difficult to communicate through text or speech alone. Sketching is therefore used for a variety of purposes, from the expression of ideas on two-dimensional (2D) physical media, to object creation, manipulation, or deformation in three-dimension...

Extensive research has been applied to discover new techniques and methods to model protein-ligand interactions. In particular, considerable efforts focused on identifying candidate binding sites, which quite often are active sites that correspond to protein pockets or cavities. Thus, these cavities play an important role in molecular docking. Howe...

In molecular biology, protein docking aims at finding the conformation in which two proteins are attached together in their native state. Several software approaches for docking already exist, which still rely on conventional interaction techniques , and have not yet taken advantage of the immersiveness nor expeditiousness made available by the new...

Interactions within virtual environments often require manipulating 3D virtual objects. To this end, researchers have endeavoured to find efficient solutions using either traditional input devices or focusing on different input modalities, such as touch and mid‐air gestures. Different virtual environments and diverse input modalities present specif...

Virtual Reality environments are able to offer natural interaction metaphors. However, it is difficult to accurately place virtual objects in the desired position and orientation using gestures in mid-air. Previous research concluded that the separation of degrees-of-freedom (DOF) can lead to better results, but these benefits come with an increase...

Context-aware pervasive applications can improve user experiences by tracking people in their surroundings. Such systems use multiple sensors to gather information regarding people and devices. However, when developing novel user experiences, researchers are left to building foundation code to support multiple network-connected sensors, a major hur...

A fundamental step in medical diagnosis for patient follow-up relies on the ability of radiologists to perform a trusty diagnostic from acquired images. Basically, the diagnosis strongly depends on the visual inspection over the shape of the lesions. As datasets increase in size, such visual evaluation becomes harder. For this reason, it is crucial...

Purpose The purpose of this paper is to explore the use of virtual reality environments (VRE) for maintenance activities by augmenting a virtual facility representation and integrating relevant information regarding the status of systems and the space itself, while providing simple ways to control them. Design/methodology/approach The research f...

In interactive systems, the ability to select virtual objects is essential. In immersive virtual environments, object selection is usually done at arm’s length in mid-air by directly intersecting the desired object with the user’s hand. However, selecting objects outside user’s arm-reach still poses significant challenges, which direct approaches f...

In Virtual Reality (VR), the action of selecting virtual objects outside arms-reach still poses significant challenges. In this work, after classifying, with a new taxonomy, and analyzing existing solutions, we propose a novel technique to perform out-of-reach selections in VR. It uses natural pointing gestures, a modifiable cone as selection volum...

Walking-in-place (WIP) is a locomotion technique that allows users to travel in virtual environments (VEs) without significantly changing their physical position on the floor. Hip-directed steering(HDS) is a novel physical technique for controlling direction changes in virtual travel using hip movements. We present an WIP-based navigation approach...

Selecting objects outside user's arm-reach in Virtual Reality still poses significant challenges. Techniques proposed to overcome such limitations often follow arm-extension metaphors or favor the use of selection volumes combined with ray-casting. Nonetheless, these approaches work for room sized and sparse environments, and they do not scale to l...

Virtual Reality (VR) is again in the spotlight. However, interactions and modeling operations are still major hurdles to its complete success. To make VR Interaction viable, many have proposed mid-air techniques because of their naturalness and resemblance to physical world operations. Still, natural mid-air metaphors for Constructive Solid Geometr...

Several studies have shown the suitability of the direct manipulation style and the multi-touch technology for kindergarteners and, as a result, direct dragging has been established as the standard way of interaction when supporting drag manipulations for them. However, there are scenarios in which direct dragging is not appropriate. For example, w...

Travel on Virtual Environments is the simple action where a user moves from a starting point A to a target point B. Choosing an incorrect type of technique could compromise the Virtual Reality experience and cause side effects such as spatial disorientation, fatigue and cybersickness. The design of effective travelling techniques demands to be as n...

Object manipulation is a key feature in almost every virtual environment. However, it is difficult to accurately place an object in immersive virtual environments using mid-air gestures that mimic interactions in the physical world, although being a direct and natural approach. Previous research studied mouse and touch based interfaces concluding t...

Manipulating objects is an essential aspect in virtual environments. Nonetheless, object positioning in immersive virtual environments relying in direct and natural approaches is still difficult. Previous research concluded that degrees-of-freedom separation in mouse and touch interfaces led to positive results. In this document we present a user e...

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 describe in detail...

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 P...

CSCW Meets Interactive SurfacesThe vast screen real estate provided in large-scale interaction environments, presents novel ways to visualize and interact with data-rich models. In parallel to this technological revolution, interactive surfaces have also become widespread in different sizes and devices, from large-scale walls to small-size handheld...

The number of available 3D digital objects has been increasing considerably. As such, searching in large collections has been subject of vast research. However, the main focus has been on algorithms and techniques for classification, indexing and retrieval. While some works have been done on query interfaces and results visualization, they do not e...

Might it be possible to discern in Raul Lino's writings _namely those published in 1918 and 1933_ the profile of a modern treatise on architecture, in the early 20th century?Drawing parallels on Alberti's "inaugural" essay (Choay, [1980], p.25), an assay precept is outlined (‘pro tem’ less conceptual than it is pragmatic), with which to approach bo...

This workshop proposes to bring together researchers who are interested in improving collaborative experiences through the use of multi-sized interaction surfaces, ranging from large-scale walls, to tables, tablets and phones. The opportunities for innovation exist, but the tabletop community has not still completely addressed the problem of bringi...

Three-dimensional virtual environments are present in many diffierent applications, being used even in small handheld devices. To navigate in these environments using such devices, most of current solutions rely on multi-touch interactions. However, previous works have already stated that multi-touch gestures on smartphones are not always feasible....

Query specification for 3D object retrieval still relies on traditional interaction paradigms. The goal of our study was to identify the most natural methods to describe 3D objects, focusing on verbal and gestural expressions. Our case study uses LEGOR blocks. We started by collecting a corpus involving ten pairs of subjects, in which one participa...

Stereoscopic tabletops offer unique visualization capabilities, enabling users to perceive virtual objects as if they were lying above the surface. While allowing virtual objects to coexist with user actions in the physical world, interaction with these virtual objects above the surface presents interesting challenges. In this paper, we aim to unde...

Virtual meetings have become increasingly common with modern video-conference and collaborative software. While they allow obvious savings in time and resources, presence is still elusive. Indeed, remote participants complain about reduced presence away from the ”main meeting”, whereas local participants have trouble noticing remote peoples’ activi...

Large Scale Displays, besides their visualization capabilities, can provide a great sense of immersion to a geographically distributed group of people engaging in collaborative work. This paper presents a system that uses remotely located wall sized displays, to offer immersive, interactive collaborative visualization and review of 3D CAD models fo...

Sketch-based 3D shape retrieval has become an important research topic in content-based 3D object retrieval. To foster this research area, two Shape Retrieval Contest (SHREC) tracks on this topic have been organized by us in 2012 and 2013 based on a small-scale and large-scale benchmarks, respectively. Six and five (nine in total) distinct sketch-b...

This workshop proposes to bring together researchers who are interested in improving collaborative experiences through the use of multi-sized interaction surfaces, ranging from large-scale walls, to tables, tablets and phones. The opportunities for innovation exist, but the tabletop community has not still completely addressed the problem of bringi...

In this paper, we present an evaluation strategy based on human-generated ground truth to measure the performance of 3D interest point detection techniques. We provide quantitative evaluation measures that relate automatically detected interest points ...

Language learning resources are constantly evolving alongside technology. Computer-Aided Language Learning (CALL) is an area of research that focuses on developing tools to improve the process of learning a language. REAP.PT is a system that aims to teach Portuguese in an appealing way, addressing issues that the user is interested in. Initially co...

The growing number of three-dimensional (3D) objects stored in digital libraries brought forth the challenge of search in D model collections. To address it, several approaches have been developed for 3D object retrieval. However, these approaches traditionally present query results as a list of thumbnails, and fail to take advantage of recent visu...

In this paper we propose the use of immersive virtual reality to visualize and explore query results in 3D object retrieval. These results are shown in a three-dimensional virtual space as 3D objects, organized according to their similarity to the query. Therefore, instead of browsing through a list of thumbnails, the user can explore the query res...

Presently, multi-touch interactive surfaces have widespread adoption as entertainment devices. Taking advantage of such devices, we present an interactive LEGO application, developed accordingly to an adaptation of building block metaphors and direct multi-touch manipulation. Our solution (LTouchIt) allows users to create 3D models on a tabletop su...

Language learning resources are constantly evolving alongside technology. One of such resources is REAP.PT, a system which aims to raise users proficiency in the Portuguese language in an interactive manner. Its current features include text-based exercises. This paper describes the evolution of REAP.PT aiming on locative prepositions used to descr...

Recently, considerable research has been carried out regarding threedimensional object manipulation on multi-touch surfaces. However, most current solutions were developed having in mind scenarios with a camera perpendicular to a scene axis, and cannot be easily used to manipulate threedimensional objects in unconstrained viewpoints. In this paper,...

The DJ culture uses a gesture lexicon strongly rooted in the traditional setup of turntables and a mixer. As novel tools are introduced in the DJ community, this lexicon is adapted to the features they provide. In particular, multitouch technologies can offer a new syntax while still supporting the old lexicon, which is desired by DJs. We present a...

Construction of LEGO models is a popular hobby, not only among children and young teenagers, but also for adults of all ages. Following the technological evolution and the integration of computers into the everyday life, several applications for virtual LEGO modelling have been created. However, these applications generally have interfaces based on...

The increasing number of three-dimensional objects available on digital format triggered a great interest in research in this domain. Finding efficient methods of analysis, comparison and retrieval of 3D models has become an important task. However, despite the existence of some benchmarks with collections of 3D models, annual contests with specifi...

Most drawing (and image) retrieval systems typically use query-by-example mechanisms or textual queries. In this chapter, we use sketches to retrieve complex vector drawings, as a solution to supplement and overcome limitations of conventional query methods. We start by describing topological and geometric information extracted from drawings and me...

A decade ago, Nakazato proposed 3D MARS, an immer-sive virtual reality environment for content-based image retrieval. Even so, the idea of taking advantage of post-WIMP interfaces for multimedia retrieval was no further explored for content-based retrieval. Considering the latest low-cost, off-the-shelf hardware for visualization and interaction, w...

Disc-jockeys have come a long way but, as far as DJing tools are concerned, there are still few applications that support hands-on interaction over Virtual DJ systems, and those are typically reduced to traditional input devices. With direct user-feedback from an accompanying group of DJ experts accounted for, we propose a Virtual DJ system with na...

Research in content-based 3D retrieval has already started, and several approaches have been proposed which use in different manner a similarity assessment to match the shape of the query against the shape of the objects in the database. However, the success of these solutions are far from the success obtained by their textual counterparts. A major...

Due to the proliferation of drafting packages, there are a lot of vector drawings available for people to integrate into documents. Moreover, creative designers and drafts-people often reuse data from previous projects and libraries of ready-to-use components. Usually, retrieving these drawings is a slow, complex and error-prone endeavor. While tex...

Simulating the dynamics of real worlds using Virtual En- vironments (VEs) is a growing area with many interesting applications. There are tools based on graphical inter- faces to create and visualise these VEs, although most of them are specific to a particular type of environment. Fol- lowing recent developments in calligraphic systems, which have...

The growth of 3D object collections and their dissemination into a wide range of application domains originated the necessity of effective retrieval solutions, similar to those that exist for textual information. However, despite the efforts of researchers during the last years, such solution was not found yet. Most of the existing retrieval soluti...

In this paper we describe a system to create LEGO models using sketches. Although there are a few applications to create LEGO models, they are difficult to use, mainly due to the searching and manipulation mechanisms that they (do not) offer. Here, we propose a sketch based approach, where users can easily insert parts, by specifying their dimensio...

Moulds are complex devices and their quotation is one of the most risky tasks in mould industry. In this paper a digital work environment based on a computer assisted mould quotation tool is proposed in which all the relevant information is quickly available to assist a robust and rapid quotation. The tool involves a new way to directly access past...

We present a shape classification technique for structural content–based retrieval of two-dimensional vector drawings. Our method has two distinguishing features. For one, it relies on explicit hierarchical descriptions of drawing structure by means of spatial relationships and shape characterization. However, unlike other approaches which attempt...

Human computer interaction techniques using hand poses are more natural to users than those that rely on devices. In this paper we describe and evaluate two techniques for hand pose recognition, based on a general library for gesture recognition, called CALI. This library was initially designed for calligraphic gesture recognition, however its usag...

Despite the considerable work on agent frameworks, user interfaces to manage these are mostly script based. Even though some solutions provide graphical interfaces to build agent worlds these are quite limited and overly dependent on textual input. Recently, calligraphic systems using sketch-based and pen-input have emerged as a viable alternative...

Current approaches to content-based retrieval of multimedia data usually rely either on query by example or on sketches of the desired image, but not on both. In this paper, we propose a new query specification scheme, where digital images are combined with sketches, after vectorization, taking advantage of both methods. We selected a set of algori...

Retrieving 2D and 3D drawings by content is not an easy task. Automatic feature extraction, indexing and matching are some of the problems raised by these approaches. We have developed a generic method to classify, index and retrieve drawings using sketches, based on spatial relationships, shape geometry and high-dimensional indexing mechanisms. Th...

Detecting polygons defined by a set of line segments in a plane is an important step in the analysis of vectorial drawings. This paper presents an approach that combines several algorithms to detect basic polygons from a set of arbitrary line segments. The resulting algorithm runs in polynomial time and space, with complexities of O((N + M) ) and O...

This paper presents a new approach to classify, index and retrieve technical draw-ings by content. Our work uses spatial relationships, shape geometry and high-dimensional indexing mechanisms to retrieve complex drawings from CAD databa-ses. This contrasts with conventional approaches which use mostly textual metadata for the same purpose. Creative...

While drawing a mould for a new design, draftspeople often consult previous projects, searching for something similar. This way they can use solutions already developed in the past, thus reducing the time required to design a new mould. However, current systems do not make this an easy task. We developed a new approach for content-based retrieval t...

Detecting polygons defined by a set of line segments in a plane is an important step in analyzing vector drawings. This paper presents an approach combining several algorithms to detect basic polygons from arbitrary line segments. The resulting algorithm runs in polynomial time and space, with complexities of O (N + M) 4 and O (N + M) 2 respectivel...