EG UK Theory and Practice of Computer Graphics

Permanent URI for this community

https://diglib.eg.org/handle/10.2312/899

Browse

Browsing EG UK Theory and Practice of Computer Graphics by Subject "and object representations"

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    Computing Curve Skeletons from Medial Surfaces of 3D Shapes
    (The Eurographics Association, 2012) Telea, Alexandru; Jalba, Andrei C.; Hamish Carr and Silvester Czanner
    Skeletons are powerful shape descriptors with many applications in shape processing, reconstruction and matching. In this paper we show that in 3D, curve skeletons can be extracted from surface skeletons in the same manner as surface skeletons can be computed from 3D object representations. Thus, the curve skeleton is conceptually the result of a recursion applied twice to a given 3D shape. To compute them, we propose an explicit advection of the surface skeleton in the implicitly-computed gradient of its distance-transform field. Through this process, surface skeleton points collapse into the sought curve skeleton. As a side result, we show how to reconstruct accurate and smooth surface skeletons from point-cloud representations thereof. Finally, we compare our method to existing state-of-the-art approaches.
  • No Thumbnail Available
    Item
    Modelling of Clouds from a Hemispherical Image
    (The Eurographics Association, 2014) Alldieck, Thiemo; Lundtoft, Dennis H.; Montanari, Niels; Nikolov, Ivan; Vlaykov, Iskren G.; Madsen, Claus B.; Rita Borgo and Wen Tang
    This paper presents an image-based method for modelling clouds. Unlike previous image-based approaches, a hemispherical photograph is used as input, enabling to consider an entire sky instead of merely a portion. Our method computes the intensity and opacity of the clouds from the photograph. For this purpose, beforehand, the sun illumination is filtered, the pixels are classified between cloud and sky pixels, and the sky behind the clouds is reconstructed. After having been smoothed, the intensity of the clouds is used to create vertices on a hemisphere, and their radius coordinate is modulated by the intensity value of the corresponding pixel. Finally, the mesh is generated by triangulation of the vertices. Additionally, the use of the opacity of the clouds to simulate their transparency and render them is proposed. The results show that our method can be used to produce a realistic full sky populated with clouds in a very straightforward way for the user.
  • No Thumbnail Available
    Item
    Topological Visualisation Techniques for the Understanding of Lattice Quantum Chromodynamics (LQCD) Simulations
    (The Eurographics Association, 2016) Thomas, Dean P.; Borgo, Rita; Hands, Simon; Cagatay Turkay and Tao Ruan Wan
    The use of topology for visualisation applications has become increasingly popular due to its ability to summarise data at a high level. Criticalities in scalar field data are used by visualisation methods such as the Reeb graph and contour trees to present topological structure in simple graph based formats. These techniques can be used to segment the input field, recognising the boundaries between multiple objects, allowing whole contour meshes to be seeded as separate objects. In this paper we demonstrate the use of topology based techniques when applied to theoretical physics data generated from Quantum Chromodynamics simulations, which due to its structure complicates their use. We also discuss how the output of algorithms involved in topological visualisation can be used by physicists to further their understanding of Quantum Chromodynamics.
  • Thumbnail Image
    Item
    Visualizing a Spherical Geological Discrete Element Model of Fault Evolution
    (The Eurographics Association, 2012) Longshaw, Stephen M.; Turner, Martin J.; Finch, Emma; Hamish Carr and Silvester Czanner
    Discrete Element Modelling (DEM) is a numerical technique that uses a system of interacting discrete bodies to simulate the movement of material being exposed to external forces. This technique is often used to simulate granular systems; however by adding further elements that inter-connect the bodies, it can be used to simulate the deformation of a large volume of material. This method has precedent for use in the Earth Sciences and recently, with the increase of available computing power, it has been put to good use simulating the evolution of extensional faults in large scale crustal experiments that involve over half a million individual spherical bodies. An interactive environment that provides high quality rendering is presented, showing that interactivity is key in allowing the intelligent application of visualization methods such as colour-mapping and visibility thresholds in order to extract fault information from a geological DEM. It is also shown that glyph representation alone is not sufficient to provide full insight into the complex three dimensional geometries of the faults found within the model. To overcome this, a novel use of the MetaBall method is described, which results in implicit surface representations of sphere sub-sets. The surfaces produced are shown to provide greater insight into the faults found within the data but also raise questions as to their meaning.
  • No Thumbnail Available
    Item
    Volumetric Spot Noise for Procedural 3D Shell Texture Synthesis
    (The Eurographics Association, 2016) Pavie, Nicolas; Gilet, Guillaume; Dischler, Jean-Michel; Galin, Eric; Ghazanfarpour, Djamchid; Cagatay Turkay and Tao Ruan Wan
    In this paper, we present an extension of the Locally Controlled Spot Noise and a visualization pipeline for volumetric fuzzy details synthesis. We extend the noise model to author volumetric fuzzy details using filtered 3D quadratic kernel functions convolved with a projective non-uniform 2D distribution of impulses. We propose a new method based on order independent splatting to compute a fast view dependent approximation of shell noise at interactive rates. Our method outperforms ray marching techniques and avoids aliasing artifacts, thus improving interactive content authoring feedback. Moreover, generated surface details share the same properties as procedural noise: they extend on potentially infinite surfaces, are defined in an extremely compact way, are non-repetitive, continuous (no discrete voxel-artifacts when zooming) and independent of the definition of the underlying surface (no surface parameterization is required).