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Recent Submissions

Topological Aspects of Maps Between Surfaces
(2022) Born, Janis
The generation of high-quality maps between surfaces of 3D shapes is a fundamental task with countless applications in geometry processing. There is a particular demand for maps that offer strict validity properties such as continuity and bijectivity, i.e. surface homeomorphisms. Such maps not only define a geometric one-to-one correspondence between surface points, but also a matching of topological features: an identification of handles and tunnels and how the map wraps around them. Finding a natural, low-distortion surface homeomorphism between a given pair of shapes is a challenging design task that involves both combinatorial (topological) and continuous (geometric) degrees of freedom. However, while powerful methods exist to improve existing homeomorphisms through continuous modifications, these are limited to merely geometric updates, and hence cannot alter map topology. In this light, it is quite surprising that most existing techniques for the initial construction of homeomorphisms do not systematically deal with questions of map topology and instead relegate these issues to user input or ad-hoc solutions. Unfortunately, this lack of reliable and automatic methods for the critically important topological initialization has so far prevented a further automation of homeomorphic surface map generation. In this thesis, we aim to close this practical gap by devising new algorithms that specifically address the map-topological issues underlying the construction of surface homeomorphisms. Our theoretical foundation is the study of the mapping class group, an algebraic structure which characterizes the entire topological design space. We approach the task of map topology generation from two different angles, based on different mapping class representations: We propose a robust method for the construction of maps from sparse landmark correspondences, based on compatible layout embeddings. Our robust embedding strategy systematically searches for short, natural embeddings and therefore reliably avoids a range of sporadic topological initialization errors which can occur with previous heuristic approaches. Additionally, we introduce a novel algorithm to extract topological map descriptions from approximate, non-homeomorphic input maps. Such a purely abstract description of map topology may then be used to guide the construction of a proper homeomorphism. As our inference method is highly robust to a wide range of map defects and imperfect map representations, this effectively allows to delegate the difficult task of finding a natural map topology to specialized shape matching methods, which have grown increasingly capable. These advancements promote the further automation of map generation techniques in two regards: They vastly reduce the need for human supervision, and make the results of automatic shape matching methods accessible for topological initialization.
Modelling and Animation of Stalactite Growth for Virtual Caves
(The Eurographics Association, 2024) Amorós-Tur, Horacio; García-Fernández, Ignacio; Marco, Julio; Patow, Gustavo
Producing large-scale scenarios in video games, animation, and the VFX industry is inherently complex and time-consuming. As a consequence, procedural modelling of landscapes, either natural or generated by human activity, is a recurring topic in computer graphics. In this paper we propose a model for the growth of stalactites that is based on physical-chemical models. The model, which is presented here for 2D landscapes, is able to generate animations of the evolution of these speleothems along time. The resulting formations are consistent with the theoretical models and with observed speleothems, and provide realistic stalactite appearance in a cave ceiling.
An Efficient Point Selection Process over a Meshlet-structured Point Cloud
(The Eurographics Association, 2024) Ortega, Lidia M.; Fernández, Juan Carlos; Collado, José Antonio; Feito, J. Francisco R.; Marco, Julio; Patow, Gustavo
Visualizing and interacting increasingly large and dense point clouds imposes the need for new methods with real-time results, where most common solutions imply a disadvantage greater than their benefit. Among the recent software and hardware advances in computer graphics and visualization, it is possible to take the concept of meshlet as a clustering of nearby points in space; this nature can bring a considerable improvement in the interaction process over the classical brute-force based algorithm, similar to common three-dimensional spatial structures. This work implements the point selection process over a meshlet-structured point cloud, assessing its performance against alternative methods and validating its correctness by visualizing the selection result on a graphical interface. By exploiting the meshlet instead of building additional spatial structures, the method's execution time can be optimized, as well as the use of the system's main memory.
Adaptation of Interaction Mechanisms in Virtual Reality Shopping Environments for People with Upper Limb Motor Difficulties
(The Eurographics Association, 2024) Grande, Rubén; Herrera, Vanesa; Glez-Morcillo, Carlos; Reyes, Ana de los; Castro-Schez, José J.; Albusac, Javier; Marco, Julio; Patow, Gustavo
In recent years, there has been research and exploration into the development of new shopping experiences within the field of electronic commerce (e-commerce). One of the technologies that can offer a more immersive shopping experience is Virtual Reality (VR). Retail giants such as Amazon and Alibaba Group have begun to use it. The technological advancement of VR, motivated by its use in various domains like e-commerce, has driven the development of software tools like APIs which allow developers to easily develop applications for these devices. One of the latest technologies included in recent VR headsets is hand tracking, which allows users to use their own hands as an input method to interact with the virtual environment. However, software tools for the development of VR applications are not fully adapted to include accessibility options for people with motor difficulties in their bodies, making it very difficult for these people to use this technology with both controllers and hand tracking. To promote accessibility options in the use of VR shopping environments, this study will present the adaptation of a set of interaction mechanisms, among which we highlight: automatic object grabbing, release of grabbed objects, navigation through the environment, attraction of distant objects, and interaction with the shopping cart. These adaptations will be made using Meta's API for Meta Quest devices as a base. The adapted environment has been tested by healthy students from the faculty and one of them with reduced mobility in the left half of his body after suffering a stroke. In this paper, we present the feedback provided by the volunteers, as well as the verification that these interaction mechanisms meet our expectations. This is an essential previous step to carry out a planned experimental session with patients with spinal cord injuries and therapist at the National Hospital for Paraplegics in Toledo (HNPT).
Dynamic Adjustment of Interactive Objects in Virtual Environments for Upper Limb Rehabilitation: A Patient-Centred Solution
(The Eurographics Association, 2024) Herrera, Vanesa; Albusac, Javier; Schez-Sobrino, Santiago; Reyes-Guzmán, Ana; Glez-Morcillo, Carlos; Marco, Julio; Patow, Gustavo
Virtual reality (VR) is a promising technology that offers physical and emotional benefits for traditional rehabilitation. However, interaction with the virtual environment can be an obstacle for patients with reduced mobility, and even more so in the case of VR-based rehabilitation, where the movements required in traditional rehabilitation have to be simulated. This difficulty highlights the need to adapt the virtual environment to the capabilities of each patient. In this study, we present a novel system designed to automatically adjust the positioning of objects within the VR environment. The system, based on data from a previous calibration, is aimed at upper limb rehabilitation, especially in patients with cervical spinal cord injury (cSCI). It incorporates algorithms capable of detecting and relocating virtual objects used in various rehabilitation exercises, ensuring better localisation within the virtual space. The main objective of this system is to improve the effectiveness of rehabilitation treatment, while facilitating adaptation to individual patient needs and exercise characteristics. Preliminary results from a pilot test with healthy subjects are promising and support the efficacy of this system, laying a solid foundation for its implementation in patients with cSCI.