Carlos Ureña

Carlos Ureña
University of Granada | UGR

PhD in Computer Science
Teaching various CS courses, research in Computer Graphics (rendering) at Universidad de Granada (Spain).

About

32
Publications
6,515
Reads
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334
Citations
Citations since 2016
4 Research Items
125 Citations
20162017201820192020202120220510152025
20162017201820192020202120220510152025
20162017201820192020202120220510152025
20162017201820192020202120220510152025
Additional affiliations
September 1992 - present
University of Granada
Position
  • Professor (Full)

Publications

Publications (32)
Article
We present a method for uniformly sampling points inside the projection of a spherical cap onto a plane through the sphere's center. To achieve this, we devise two novel area‐preserving mappings from the unit square to this projection, which is often an ellipse but generally has a more complex shape. Our maps allow for low‐variance rendering of dir...
Article
Full-text available
Presentamos nuevos métodos para la estimación eficiente de la radiancia incidente proveniente de fuentes de luz con forma de disco. Por ello, introducimos tres nuevos mapeos conformes por área de la proyección en ángulo sólido del disco. Nuestros métodos mejoran significativamente el trabajo preexistente, y han sido implementado en un motor de rend...
Article
The computational simulation of shallow stratified fluids is a very active research topic because these types of systems are very common in a variety of natural environments. The simulation of such systems can be modeled using multilayer shallow-water equations but do impose important computational requirements, especially when applied to large dom...
Article
Full-text available
We present new methods for uniformly sampling the solid angle subtended by a disk. To achieve this, we devise two novel area-preserving mappings from the unit square [0,1]2 to a spherical ellipse (i.e. the projection of the disk onto the unit sphere). These mappings allow for low-variance stratified sampling of direct illumination from disk-shaped...
Article
Full-text available
This paper presents an analysis of the overestimation bias in common used filtering kernels in the context of photon mapping density estimation. We use the joint distribution of order statistics to calculate the expected value of the estimators of irradiance, and show that the estimator provided by the cone filter is not consistent unless the slope...
Article
We present an area-preserving parametrization for spherical rectangles which is an analytical function with domain in the unit rectangle [0, 1]2 and range in a region included in the unit-radius sphere. The parametrization preserves areas up to a constant factor and is thus very useful in the context of rendering as it allows to map random sample p...
Article
This paper presents an analysis of the irradiance estimator often used in photon mapping algorithms and concludes that the classical approach with a constant kernel overestimates the correct value. We propose a new estimator that solves this problem and provide both theoretical and empirical studies to verify it.
Article
This paper addresses the speedup of the numerical solution of shallow-water systems in 2D domains by using modern graphics processing units (GPUs). A first order well-balanced finite volume numerical scheme for 2D shallow-water systems is considered. The potential data parallelism of this method is identified and the scheme is efficiently implement...
Article
We address the speedup of the nume- rical solution of shallow water systems in 2D do- mains by using modern Graphics Processing Units. We have considered a first order well-balanced finite volume numerical scheme for 2D shallow water sys- tems. The potential data parallelism of this method has been identified and an efficient implementation of this...
Conference Paper
Full-text available
Abstract This article presents an optimized ray tracing algorithm which improves standard existing algorithms. In order to do this, this algorithm processes simultaneously a large set of rays and carries out a single traversal of the spatial indexing of the scene with all rays, which allows us to efficiently make use of hardware SIMD functionality...
Conference Paper
Full-text available
This paper introduces a new BRDF sampling method with reduced variance, which is based on a hierarchical adaptive PDF. This PDF also is based on rejection sampling with a bounded average number of trials, even in regions where the BRDF exhibits high variations. Our algorithm works in an appropiate way with both physical, analytical and measured ref...
Article
Full-text available
Este artículo presenta un método de estimación de densidades basado en rayos que ha sido implementado com- pletamente en la GPU. La estimación de densidades basada en rayos reduce el sesgo de los enfoques clásicos basados en fotones aunque tiene un costo computacional más alto. Proponemos algoritmos y estructuras de datos para la implementación en...
Conference Paper
Full-text available
This paper introduces a new BRDF sampling method with reduced variance, which is based on a hierarchical adaptive parameterless PDF. This PDF is based also on rejection sampling with a bounded average number of trials, even in regions where the BRDF does exhibit high variations. Our algorithm works in an appropiate way with both physical and analyt...
Conference Paper
Full-text available
Global illumination solutions provide a very accurate representation of illumination. However, they are usually costly to calculate. In the common case of quasi-static scenario, in which most of the scene is static and only a few objects move, most of the illumination can be reused from previous frames, yielding increased performance. This article...
Article
Full-text available
Resumen Este artículo compara empírica y teóricamente varias optimizaciones de estimación de densidades en el plano tangente, que es una técnica para ilumi-nación global. Esta técnica se basa en Photon Maps y da más exactitud si las superficies no son local-mente suaves o continuas. La primera de las op-timizaciones crea un conjunto de rayos candid...
Article
Full-text available
Density estimation on the tangent plane (DETP) is a density estimation technique for global illumination. This technique is based on Photon Maps and provides increased accuracy when the surfaces are not locally smooth or continuous. However, the performance of the technique is limited by the large number of ray-disc intersections needed. Some optim...
Conference Paper
Full-text available
This paper describes an approach to obtain interactive recalculation of global illumination for scenes with small moving objects (with respect to the complete geometry), on a standard PC, using density estimation techniques
Article
Full-text available
The ray-scene intersection test is the most costly process when a scene is rendered. This process may be improved using any strategy to be able to speed-up it. Generally, any strategy used is based on the building of a spatial indexing in the scene domain or in the rays domain. However, there is no theory to formalize these techniques. In this pape...
Article
Full-text available
Radiosity computation on scenes including objects with a complex geometry, or with a large number of faces and meshes with very different sizes, is very complex. We present a new method (based on the Photon Maps method [7]) where density estimation on the tangent plane at each surface point is performed for irradiance computation by using photon pa...
Article
Full-text available
Radiosity computation on scenes including objects with a complex geometry, or with a large number of faces and meshes with very different sizes, is very complex. We present a new method (based on the photon maps method 6) where density estimation on the tangent plane at each surface point is performed for irradiance computation by using photon path...
Article
Full-text available
The ray-scene intersection test is the most costly process when a scene is rendered. This process may be improved using any strategy to be able to speed-up it. Generally, any strategy used is based on the building of a spatial indexing in the scene domain or in the rays domain. In this paper, an acceleration techniques formalization is proposed. Th...
Article
We introduce an algorithm for sample positioning in a planar triangle, which can be used to make numerical integration of an arbitrary function defined on it. This algorithm has some interesting properties which make it suitable for applica- tions in the context of realistic rendering. We use an adapti ve triangle partitioning procedure, driven by...
Article
Full-text available
An octree is a well known hierarchical spatial structure which is widely used in Computer Graphics algorithms. One of the most frequent operations is the computation of the octree voxels intersected by a straight line. This has a number of applications, such as ray-object intersection tests speed-up and visualisation of hierarchical density models...
Article
Full-text available
This paper describes the design of an object oriented rendering system. The system has been designed as part of a research project whose goal is to investigate the influence of different aspects of the rendering process on the quality of the resulting image. The interest areas include: the representation of energies and colours, the indexing method...
Article
This report presents a classification of global illumination methods, focusing on the numerical algorithms used. The methods are grouped in several categories, and described by using a common theoretical formalism, which indicates the similarities and differences between them. This formalism is based on the notion of integral and projection operato...
Conference Paper
In this paper we consider the task of refining a low-resolution radiosity solution by using final gather. This final gather can be done by using Monte-Carlo methods. We show how to built an adequate probability density function (pdf) such that the involved variance is greatly reduced and thus we can reduce the number of samples to take, keeping the...
Article
Object-oriented techniques can be applied, in a natural way, to computer graphics. Traditionally, these techniques have been used for the design of graphic user interfaces, but recently, they have been applied to other computer graphic fields. This paper presents the design of a ray-tracing rendering program. The program has been built using a clas...
Conference Paper
Full-text available
In this paper a feature-map based system for protein classification according to circular dichroism spectra is described. The training algorithm has been developed from Kohonen LVQ (Learning Vector Quantization) optimized to get maximum efficiency. As a result, proteins with different secondary structure are clearly separated through a completely u...

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Project (1)
Project
Efficient implementation for area-preserving parametrizations of spherical regions, obtained as projections of simple geometrical objects: spherical rectangles, disk, ellipses, ellipsoids, perhaps others.....