Ambient occlusion and shadows for molecular graphics

Computer based visualisations of molecules have been produced as early as the 1950s to aid researchers in their understanding of biomolecular structures. An important consideration for Molecular Graphics software is the ability to visualise the 3D structure of the molecule in a clear manner. Recent advancements in computer graphics have led to improved rendering capabilities of the visualisation tools. The capabilities of current shading languages allow the inclusion of advanced graphic effects such as ambient occlusion and shadows that greatly improve the comprehension of the 3D shapes of the molecules. This thesis focuses on finding improved solutions to the real time rendering of Molecular Graphics on modern day computers. The methods of calculating ambient occlusion and both hard and soft shadows are examined and implemented to give the user a more complete experience when navigating large molecular structures

3D object reconstruction using computer vision : reconstruction and characterization applications for external human anatomical structures

Tese de doutoramento. Engenharia Informática. Faculdade de Engenharia. Universidade do Porto. 201

Surface analysis and fingerprint recognition from multi-light imaging collections

Multi-light imaging captures a scene from a fixed viewpoint through multiple photographs, each of which are illuminated from a different direction. Every image reveals information about the surface, with the intensity reflected from each point being measured for all lighting directions. The images captured are known as multi-light image collections (MLICs), for which a variety of techniques have been developed over recent decades to acquire information from the images. These techniques include shape from shading, photometric stereo and reflectance transformation imaging (RTI). Pixel coordinates from one image in a MLIC will correspond to exactly the same position on the surface across all images in the MLIC since the camera does not move. We assess the relevant literature to the methods presented in this thesis in chapter 1 and describe different types of reflections and surface types, as well as explaining the multi-light imaging process. In chapter 2 we present a novel automated RTI method which requires no calibration equipment (i.e. shiny reference spheres or 3D printed structures as other methods require) and automatically computes the lighting direction and compensates for non-uniform illumination. Then in chapter 3 we describe our novel MLIC method termed Remote Extraction of Latent Fingerprints (RELF) which segments each multi-light imaging photograph into superpixels (small groups of pixels) and uses a neural network classifier to determine whether or not the superpixel contains fingerprint. The RELF algorithm then mosaics these superpixels which are classified as fingerprint together in order to obtain a complete latent print image, entirely contactlessly. In chapter 4 we detail our work with the Metropolitan Police Service (MPS) UK, who described to us with their needs and requirements which helped us to create a prototype RELF imaging device which is now being tested by MPS officers who are validating the quality of the latent prints extracted using our technique. In chapter 5 we then further developed our multi-light imaging latent fingerprint technique to extract latent prints from curved surfaces and automatically correct for surface curvature distortions. We have a patent pending for this method

Ray Tracing Gems

This book is a must-have for anyone serious about rendering in real time. With the announcement of new ray tracing APIs and hardware to support them, developers can easily create real-time applications with ray tracing as a core component. As ray tracing on the GPU becomes faster, it will play a more central role in real-time rendering. Ray Tracing Gems provides key building blocks for developers of games, architectural applications, visualizations, and more. Experts in rendering share their knowledge by explaining everything from nitty-gritty techniques that will improve any ray tracer to mastery of the new capabilities of current and future hardware. What you'll learn: The latest ray tracing techniques for developing real-time applications in multiple domains Guidance, advice, and best practices for rendering applications with Microsoft DirectX Raytracing (DXR) How to implement high-performance graphics for interactive visualizations, games, simulations, and more Who this book is for: Developers who are looking to leverage the latest APIs and GPU technology for real-time rendering and ray tracing Students looking to learn about best practices in these areas Enthusiasts who want to understand and experiment with their new GPU

Being-in-the-world in terms of place and its relations to the work of art in Yi-Fu Tuan, Gaston Bachelard, and Martin Heidegger

This thesis aims to examine the notion of place in our being-in-the-world. The special concern of the thesis is to investigate the role of the work of art in the awakening of an experience that creates place. My intention is to investigate how place, as a worldly spatial experience, can be manifest via a work of art. Drawing from the work of Yi-Fu Tuan, Gaston Bachelard, and Martin Heidegger, place is understood to be the result of human perception, interaction, and experiences with space and the objects contained within, while place is defined as open, uncertain, and free, containing a possibility for movement and change, and is readily available around us. Once interacted with, experiences in space are set as memories, images of our past, and tie to the location of their happening, their setting place. As a form of truth, place belongs to aletheia, meaning it is a truth that comes out of concealment, a mode of disclosure that reveals a way of being. Following Heidegger, I argue that art is able to play a unique role in this disclosure. My examination of this role centres upon the remarkable significance of art found in Australia’s First Nation people’s relationship with place is as shown in the traditional Songlines and their expression in songs and paintings. These artistic expressions enable one to create place out of space without visiting its physical location, meaning without experiencing it first hand, and communicate this experience to others

Study of the interaction with a virtual 3D environment displayed on a smartphone

Les environnements virtuels à 3D (EV 3D) sont de plus en plus utilisés dans différentes applications telles que la CAO, les jeux ou la téléopération. L'évolution des performances matérielles des Smartphones a conduit à l'introduction des applications 3D sur les appareils mobiles. En outre, les Smartphones offrent de nouvelles capacités bien au-delà de la communication vocale traditionnelle qui sont consentis par l'intégrité d'une grande variété de capteurs et par la connectivité via Internet. En conséquence, plusieurs intéressantes applications 3D peuvent être conçues en permettant aux capacités de l'appareil d'interagir dans un EV 3D. Sachant que les Smartphones ont de petits et aplatis écrans et que EV 3D est large, dense et contenant un grand nombre de cibles de tailles différentes, les appareils mobiles présentent certaines contraintes d'interaction dans l'EV 3D comme : la densité de l'environnement, la profondeur de cibles et l'occlusion. La tâche de sélection fait face à ces trois problèmes pour sélectionner une cible. De plus, la tâche de sélection peut être décomposée en trois sous-tâches : la Navigation, le Pointage et la Validation. En conséquence, les chercheurs dans un environnement virtuel 3D ont développé de nouvelles techniques et métaphores pour l'interaction en 3D afin d'améliorer l'utilisation des applications 3D sur les appareils mobiles, de maintenir la tâche de sélection et de faire face aux problèmes ou facteurs affectant la performance de sélection. En tenant compte de ces considérations, cette thèse expose un état de l'art des techniques de sélection existantes dans un EV 3D et des techniques de sélection sur Smartphone. Il expose les techniques de sélection dans un EV 3D structurées autour des trois sous-tâches de sélection: navigation, pointage et validation. En outre, il décrit les techniques de désambiguïsation permettant de sélectionner une cible parmi un ensemble d'objets présélectionnés. Ultérieurement, il expose certaines techniques d'interaction décrites dans la littérature et conçues pour être implémenter sur un Smartphone. Ces techniques sont divisées en deux groupes : techniques effectuant des tâches de sélection bidimensionnelle sur un Smartphone et techniques exécutant des tâches de sélection tridimensionnelle sur un Smartphone. Enfin, nous exposons les techniques qui utilisaient le Smartphone comme un périphérique de saisie. Ensuite, nous discuterons la problématique de sélection dans un EV 3D affichée sur un Smartphone. Il expose les trois problèmes identifiés de sélection : la densité de l'environnement, la profondeur des cibles et l'occlusion. Ensuite, il établit l'amélioration offerte par chaque technique existante pour la résolution des problèmes de sélection. Il analyse les atouts proposés par les différentes techniques, la manière dont ils éliminent les problèmes, leurs avantages et leurs inconvénients. En outre, il illustre la classification des techniques de sélection pour un EV 3D en fonction des trois problèmes discutés (densité, profondeur et occlusion) affectant les performances de sélection dans un environnement dense à 3D. Hormis pour les jeux vidéo, l'utilisation d'environnement virtuel 3D sur Smartphone n'est pas encore démocratisée. Ceci est dû au manque de techniques d'interaction proposées pour interagir avec un dense EV 3D composé de nombreux objets proches les uns des autres et affichés sur un petit écran aplati et les problèmes de sélection pour afficher l' EV 3D sur un petit écran plutôt sur un grand écran. En conséquence, cette thèse se concentre sur la proposition et la description du fruit de cette étude : la technique d'interaction DichotoZoom. Elle compare et évalue la technique proposée à la technique de circulation suggérée par la littérature. L'analyse comparative montre l'efficacité de la technique DichotoZoom par rapport à sa contrepartie. Ensuite, DichotoZoom a été évalué selon les différentes modalités d'interaction disponibles sur les Smartphones. Cette évaluation montre la performance de la technique de sélection proposée basée sur les quatre modalités d'interaction suivantes : utilisation de boutons physiques ou sous forme de composants graphiques, utilisation d'interactions gestuelles via l'écran tactile ou le déplacement de l'appareil lui-même. Enfin, cette thèse énumère nos contributions dans le domaine des techniques d'interaction 3D utilisées dans un environnement virtuel 3D dense affiché sur de petits écrans et propose des travaux futurs.3D Virtual Environments (3D VE) are more and more used in different applications such as CAD, games, or teleoperation. Due to the improvement of smartphones hardware performance, 3D applications were also introduced to mobile devices. In addition, smartphones provide new computing capabilities far beyond the traditional voice communication. They are permitted by the variety of built-in sensors and the internet connectivity. In consequence, interesting 3D applications can be designed by enabling the device capabilities to interact in a 3D VE. Due to the fact that smartphones have small and flat screens and that a 3D VE is wide and dense with a large number of targets of various sizes, mobile devices present some constraints in interacting on the 3D VE like: the environment density, the depth of targets and the occlusion. The selection task faces these three problems to select a target. In addition, the selection task can be decomposed into three subtasks: Navigation, Pointing and Validation. In consequence, researchers in 3D virtual environment have developed new techniques and metaphors for 3D interaction to improve 3D application usability on mobile devices, to support the selection task and to face the problems or factors affecting selection performance. In light of these considerations, this thesis exposes a state of the art of the existing selection techniques in 3D VE and the selection techniques on smartphones. It exposes the selection techniques in 3D VE structured around the selection subtasks: navigation, pointing and validation. Moreover, it describes disambiguation techniques providing the selection of a target from a set of pre-selected objects. Afterward, it exposes some interaction techniques described in literature and designed for implementation on Smartphone. These techniques are divided into two groups: techniques performing two-dimensional selection tasks on smartphones, and techniques performing three-dimensional selection tasks on smartphones. Finally, we expose techniques that used the smartphone as an input device. Then, we will discuss the problematic of selecting in 3D VE displayed on a Smartphone. It exposes the three identified selection problems: the environment density, the depth of targets and the occlusion. Afterward, it establishes the enhancement offered by each existing technique in solving the selection problems. It analysis the assets proposed by different techniques, the way they eliminates the problems, their advantages and their inconvenient. Furthermore, it illustrates the classification of the selection techniques for 3D VE according to the three discussed problems (density, depth and occlusion) affecting the selection performance in a dense 3D VE. Except for video games, the use of 3D virtual environment (3D VE) on Smartphone has not yet been popularized. This is due to the lack of interaction techniques to interact with a dense 3D VE composed of many objects close to each other and displayed on a small and flat screen and the selection problems to display the 3D VE on a small screen rather on a large screen. Accordingly, this thesis focuses on defining and describing the fruit of this study: DichotoZoom interaction technique. It compares and evaluates the proposed technique to the Circulation technique, suggested by the literature. The comparative analysis shows the effectiveness of DichotoZoom technique compared to its counterpart. Then, DichotoZoom was evaluated in different modalities of interaction available on Smartphones. It reports on the performance of the proposed selection technique based on the following four interaction modalities: using physical buttons, using graphical buttons, using gestural interactions via touchscreen or moving the device itself. Finally, this thesis lists our contributions to the field of 3D interaction techniques used in a dense 3D virtual environment displayed on small screens and proposes some future works

Large bichromatic point sets admit empty monochromatic 4-gons

We consider a variation of a problem stated by Erd˝os and Szekeres in 1935 about the existence of a number fES(k) such that any set S of at least fES(k) points in general position in the plane has a subset of k points that are the vertices of a convex k-gon. In our setting the points of S are colored, and we say that a (not necessarily convex) spanned polygon is monochromatic if all its vertices have the same color. Moreover, a polygon is called empty if it does not contain any points of S in its interior. We show that any bichromatic set of n ≥ 5044 points in R2 in general position determines at least one empty, monochromatic quadrilateral (and thus linearly many).Postprint (published version

Perspective in Two Dimensions for Computer Graphics

Computer graphics perspective is based on photography, the pin-hole camera model. This thesis examines the perspective as practiced by artists, who develop the picture geometry within the planar surface of the canvas. Their approach is flexible, depth is simulated with planar composition as the primary geometry. Renaissance artists discovered construction methods to draw the foreshortening of realistic pictures: the construction of a tiled floor in perspective was fundamental. This thesis presents the framework, a computer program, I developed to create the perspective of pictures based on the geometry practices of artists. Construction lines on the image plane simulate the 3D geometry of the pictorial space; cartoons of foreground elements are manipulated in 2D within the picture perspective; projected shadows, examples of double projection, are also included. A formalism, reformulating algebraically the straight-edge and compass evaluations, generalizes the planar geometry that solves the challenge of depicting 3D. A revised Painter’s algorithm produces the occlusions between the picture elements from sequencing them from their definitions on the canvas