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Item Study of the Influence of User Characteristics on the Virtual Reality Presence(The Eurographics Association, 2018) Mayor, Jesús; Sánchez, Alberto; Raya, Laura; García-Fernández, Ignacio and Ureña, CarlosIn recent years, virtual reality has grown a lot in different areas of application, including ludic, social and research, being used by a large and growing number of users with different profiles. Presence is one of the most distinctive and important features of a virtual reality experience. The aim of this article is to study the most suitable areas of application for users and to analyze the influence of different characteristics of the user's profile in the perceived presence. We have tested the interest applications indicated by 159 subjects and we have designed an immersive virtual reality experience, testing the behavior and performance of 48 users. The results obtained show that gender can influence the perceptual sensation of presence in these types of virtual environments.Item Modelling the Fluid-Boundary Interaction in SPH(The Eurographics Association, 2018) Perea, Juan J.; Cordero, Juan M.; García-Fernández, Ignacio and Ureña, CarlosSmoothed Particle Hydrodynamics (SPH) is a numerical method based on mutually interacting meshfree particles, and has been widely applied to fluid simulation in Computer Graphics. Originally SPH does not define the behaviour of the particle system in the contour, so the different variants of SPH have been solving this deficiency with different techniques. Some of these techniques are based on fictitious forces, specular particles or semi-analytic fields. However, all these proposals present a drawback, that are may introduce additional inaccuracy as a divergent behaviour of the particle dynamics or an artificial separation between the fluid limits and the contour. To solve these limitations at this paper presents a new technique based on contour particles that are used during simulation to model the interaction with the fluid. The use of contour particles had already been used in other works to construct the contour like a particle layer. That solution presents problems especially when increasing the complexity of the contour shape. In addition, unlike other techniques, this paper presents an additional advantage, the possibility of obtaining all the dynamic magnitudes for improving efficiency and versatility.Item Cylindrical Transform Slicing of Revolute Parts with Overhangs for Laser Metal Deposition(The Eurographics Association, 2022) Montoya-Zapata, Diego; Moreno, Aitor; Ortiz, Igor; Ruiz-Salguero, Oscar; Posada, Jorge; Posada, Jorge; Serrano, AnaIn the context of Laser Metal Deposition (LMD), temporary support structures are needed to manufacture overhanging features. In order to limit the need for supports, multi-axis machines intervene in the deposition by sequentially repositioning the part. Under multi-axis rotations and translations, slicing and toolpath generation represent significant challenges. Slicing has been partially addressed by authors in multi-axis LMD. However, tool-path generation in multi-axis LMD is rarely touched. One of the reasons is that the required slices for LMD may be strongly non-developable. This fact produces a significant mismatch between the tool-path speeds and other parameters in Parametric space vs. actual Euclidean space. For the particular case of developable slices present in workpieces with cylindrical kernel and overhanging neighborhoods, this manuscript presents a methodology for LMD tool path generation. Our algorithm takes advantage of existing cylindrical iso-radial slicing by generating a path in the (?, z) parameter space and isometrically translating it into the R3 Euclidean space. The presented approach is advantageous because it allows the path-planning of complex structures by using the methods for conventional 2.5-axis AM. Our computer experiments show that the presented approach can be effectively used in manufacturing industrial/mechanical pieces (e.g., spur gears). Future work includes the generation of the machine g-code for actual LMD equipment.Item Modal Locomotion of C. elegans(The Eurographics Association, 2019) Mujika, Andoni; Merino, Sara; Leškovský, Peter; Epelde, Gorka; Oyarzun, David; Otaduy, Miguel Angel; Casas, Dan and Jarabo, AdriánCaenorhabditis elegans (C. elegans) is a roundworm that, thanks to its combination of biological simplicity and behavioral richness, offers an excellent opportunity for initial experimentation of many human diseases. In this work, we introduce a locomotion model for C. elegans, which can enable in-silico validation of behavioral experiments prior to physical experimentation with actual C. elegans specimens. Our model enables interactive simulation of self-propelling C. elegans, using as sole input biologically inspired muscle forces and frictional contact. The key to our model is a simple locomotion control strategy that activates selected natural vibration modes of the worm. We perform an offline analysis of the natural vibration modes, select those that best match the deformation of the worm during locomotion, and design force profiles that activate these vibration modes in a coordinated manner. Together with force compensation for momentum conservation and an anisotropic friction model, we achieve locomotions that match qualitatively those of real-world worms. Our approach is general, and could be extended to the locomotion of other types of animals or characters.Item Perfect Spatial Hashing for Point-cloud-to-mesh Registration(The Eurographics Association, 2019) Mejia-Parra, Daniel; Lalinde-Pulido, Juan; Sánchez, Jairo R.; Ruiz-Salguero, Oscar; Posada, Jorge; Casas, Dan and Jarabo, AdriánPoint-cloud-to-mesh registration estimates a rigid transformation that minimizes the distance between a point sample of a surface and a reference mesh of such a surface, both lying in different coordinate systems. Point-cloud-to-mesh-registration is an ubiquitous problem in medical imaging, CAD CAM CAE, reverse engineering, virtual reality and many other disciplines. Common registration methods include Iterative Closest Point (ICP), RANdom SAmple Consensus (RANSAC) and Normal Distribution Transform (NDT). These methods require to repeatedly estimate the distance between a point cloud and a mesh, which becomes computationally expensive as the point set sizes increase. To overcome this problem, this article presents the implementation of a Perfect Spatial Hashing for point-cloud-to-mesh registration. The complexity of the registration algorithm using Perfect Spatial Hashing is O(NYxn) (NY : point cloud size, n: number of max. ICP iterations), compared to standard octrees and kd-trees (time complexity O(NY log(NT)xn), NT : reference mesh size). The cost of pre-processing is O(NT +(N3H )2) (N3H : Hash table size). The test results show convergence of the algorithm (error below 7e-05) for massive point clouds / reference meshes (NY = 50k and NT = 28055k, respectively). Future work includes GPU implementation of the algorithm for fast registration of massive point clouds.Item A Prototype of Virtual Reality System for the Visualization, Exploration and Modeling of Huge Point Clouds(The Eurographics Association, 2018) Ortega-Donaire, José; Segura-Sánchez, Rafael Jesús; Ogáyar-Anguita, Carlos-Javier; Rueda-Ruiz, Antonio Jesús; García-Fernández, Ignacio and Ureña, CarlosThe use of specific techniques for the management and visualization of huge point clouds is necessary to solve the drawbacks of inefficiency derived from the size of the dataset and the techniques used to visualize it. This work presents a prototype of VR system for the visualization and management of extensive point clouds in 3D with the ability to edit specific points. For this, the tool incorporates multiresolution techniques, which improve the performance and efficiency of the system. The prototype also incorporates the management of the point cloud stored in an unstructured database; so the prototype can request parts of the dataset from the required fractions generated by an octree. This allows the progressive processing of 3D point clouds, which is very useful to control and visualize a large data set in real time.Item Rendering and Interacting With Volume Models in Immersive Environments(The Eurographics Association, 2018) Fons, Joan; Monclús, Eva; Vázquez, Pere-Pau; Navazo, Isabel; García-Fernández, Ignacio and Ureña, CarlosThe recent advances in VR headsets, such as the Oculus Rift or HTC Vive, at affordable prices offering a high resolution display, has empowered the development of immersive VR applications. data. In this paper we propose an immersive VR system that uses some well-known acceleration algorithms to achieve real-time rendering of volumetric datasets in an immersive VR system. Moreover, we have incorporated different basic interaction techniques to facilitate the inspection of the volume dataset. The interaction has been designed to be as natural as possible in order to achieve the most comfortable, user-friendly virtual experience. We have conducted an informal user study to evaluate the user preferences. Our evaluation shows that our application is perceived usable, easy of learn and very effective in terms of the high level of immersion achieved.Item Procedural Location of Roads Using Desire Paths(The Eurographics Association, 2019) Real, Pablo; Martínez-Gil, Francisco; Martínez-Durá, Rafael J.; García-Fernández, Ignacio; Casas, Dan and Jarabo, AdriánProcedural modelling of realistic environments that include elements derived from human activity can largely reduce production cost in animation, video-games and feature films. We address the problem of placing roads and other human-made elements, such as buildings, in a way that is consistent with the scene relief. Our approach is based on the calculation of so called desire paths, by means of the generation of many optimal paths according to different cost or distance functions. Using this idea, we rely on the information of the terrain properties to emulate the exploration of the scenario by a large number of pedestrians. From the routes generated by the pedestrians, we define walkability and habitability maps on the scene that can be later used to locate roads or buildings.Item Extending Industrial Digital Twins with Optical Object Tracking(The Eurographics Association, 2017) Tammaro, Antonio; Segura, Álvaro; Moreno, Aitor; Sánchez, Jairo R.; Fco. Javier Melero and Nuria PelechanoIn the last year, the concept of Industry 4.0 and smart factories has increasingly gained more importance. One of the central aspects of this innovation is the coupling of physical systems with a corresponding virtual representation, known as the Digital Twin. This technology enables new powerful applications, such as real-time production optimization or advanced cloud services. To ensure the real-virtual equivalence it is necessary to implement multimodal data acquisition frameworks for each production system using their sensing capabilities, as well as appropriate communication and control architectures. In this paper we extend the concept of the digital twin of a production system adding a virtual representation of its operational environment. In this way the paper describes a proof of concept using an industrial robot, where the objects inside its working volume are captured by an optical tracking system. Detected objects are added to the digital twin model of the cell along with the robot, having in this way a synchronized virtual representation of the complete system that is updated in real time. The paper describes this tracking system as well as the integration of the digital twin in a Web3D based virtual environment that can be accessed from any compatible devices such as PCs, tablets and smartphones.Item Guided Modeling of Natural Scenarios: Vegetation and Terrain(The Eurographics Association, 2022) Collado, José Antonio; López, Alfonso; Pérez, Juan Roberto Jiménez; Ortega, Lidia M.; Jurado, Juan M.; Feito, Francisco; Posada, Jorge; Serrano, AnaThe generation of realistic natural scenarios is a longstanding and ongoing challenge in Computer Graphics. LiDAR (Laser Imaging Detection and Ranging) point clouds have been gaining interest for the representation and analysis of real-world scenarios. However, the output of these sensors is conditioned by several parameters, including, but not limited to, distance to scanning target, aperture angle, number of laser beams, as well as systematic and random errors for the acquisition process. Hence, LiDAR point clouds may present inaccuracies and low density, thus hardening their visualization. In this work, we propose reconstructing the surveyed environments to enhance the point cloud density and provide a 3D representation of the scenario. To this end, ground and vegetation layers are detected and parameterized to allow their reconstruction. As a result, point clouds of any required density can be modeled, as well as 3D realistic natural scenarios that may lead to procedural generation through their parameterization.