Francesc Castro

Point sampling with uniformly distributed lines

In this paper we address the problem of extracting representative point samples from polygonal models. The goal of such a sampling algorithm is to find points that are evenly distributed. We propose star-discrepancy as a measure for sampling quality and propose new sampling methods based on global line distributions. We investigate several line generation algorithms including an efficient hardware-based sampling method. Our method contributes to the area of point-based graphics by extracting points that are more evenly distributed than by sampling with current algorithms.

Energy-saving light positioning using heuristic search

A new definition is given to the problem of light positioning in a closed environment, aiming at obtaining, for a global illumination radiosity solution, the position and emission power for a given number of lights that provide a desired illumination at a minimum total emission power. Such a desired illumination is expressed using minimum and/or maximum values of irradiance allowed, resulting in a combinatory optimization problem. A pre-process computes and stores irradiances for a pre-established set of light positions by means of a radiosity random walk. The reuse of photon paths makes this pre-process reasonably cheap. Different heuristic search algorithms, combined to linear programming, are discussed and compared, from the simplest hill climbing strategies to the more sophisticated population-based and hybrid approaches. The paper shows how the presented approaches make it possible to obtain a good solution to the problem at a reasonable cost.

Efficient reuse of paths for random walk radiosity

Global illumination algorithms take into account not only the direct illumination but also the indirect one, i.e., all reflections of light. Radiosity is one global illumination model which relies on computing the amount of light transferred between the surfaces in a scene, assuming these surfaces to be ideal diffuse or Lambertian reflectors.Numerous algorithms have been proposed to find the radiosity solution of an environment. Some of them use Monte Carlo random paths. The main drawback of such techniques is their high computational cost, due to the large number of samples (paths) needed to obtain an acceptable result. The reuse of paths is a valid strategy to reduce this cost. This article analyzes in detail the techniques of reusing paths in the radiosity context for both static scenes and light animation. A noticeable gain has been obtained in our experiments.

Extended ambient term

Abstract The ambient term in a renderer is a constant color added to all points yielding a crude global approximation to indirect lighting. Because the ambient term ignores geometric occlusion conditions, it is computationally inexpensive. We present an extended ambient term that provides better results than the constant term but is still inexpensive, because it also does not compute occlusion conditions. It is based on the idea of finding a six-sided axis-aligned environment which is similar in color and area to the real scene, and deriving an approximation to indirect lighting by computing interreflections in the simplified scene.

Heuristic-Search-Based Light Positioning According to Irradiance Intervals

We present a strategy to solve the problem of light positioning in a closed environment. We aim at obtaining, for a global illumination radiosity solution, the position and emission power for a given number of lights that provide a desired illumination at a minimum total emission power. Such a desired illumination is expressed using minimum and/or maximum values of irradiance allowed. A pre-process is needed in which irradiance is computed for a pre-established set of light positions by means of a random walk. The reuse of paths makes this pre-process reasonably cheap. Different heuristic-search strategies are explored and compared in our work, which, combined to linear programming, make it possible to efficiently visit the search space and, in most cases, obtain a good solution at a reasonable cost.

Fast Multipath Radiosity using Hierarchical Subscenes

This paper presents an efficient acceleration technique for the global line radiosity Multipath method. In this approach, the scene is subdivided in a hierarchy of box bounded subscenes, the boxes subdivided in a grid of virtual patches which store angular information. A new recursive (according to the hierarchy of subscenes) function allows to execute the Multipath algorithm at different levels of the hierarchy. A speed up factor up to 3–4 has been obtained on some of the tested scenes.

Reuse of Paths in Final Gathering Step with Moving Light Sources

In this paper we extend our previous result on reusing shooting paths when dealing with moving light sources in radiosity to the final gathering step algorithm, which combines a shooting solution and a gathering step. Paths are reused for each frame in both shooting and gathering steps, obtaining a noticeable reduction of cost in the computation of the solutions for every frame. Moreover, the correlation between consecutive frames happens to be higher than in the case of independent solutions, resulting in a clear reduction of the temporal aliasing effects in the animation.

Using peer assessment to evaluate teamwork from a multidisciplinary perspective

Abstract This article analyses the use of peer evaluation as a tool for evaluating teamwork and students’ perceptions of this type of evaluation. A study was conducted of six subjects included on five degree courses at the University of Girona. In all of these subjects, students carried out a team activity, evaluated the performance of the team and the involvement of its different members, and responded to a survey on their perceptions of this evaluation system. We found the main factors influencing the evaluation and perception of teamwork to be teachers’ and students’ prior experience in this type of evaluation activity, the field where it is applied, the academic year students are enrolled on and the weight of the activity in the final mark. The results show that, in general, students’ views regarding such evaluation procedures are positive.

Incremental reuse of paths in random walk radiosity

Radiosity techniques produce highly realistic synthetic images for diffuse environments Monte Carlo random walk approaches, widely applied to radiosity, have as a drawback the necessity of a high number of random paths to obtain an acceptable result, involving a high computation cost The reuse of paths is a strategy to reduce this cost, allowing that a path distributes light power from several light positions, resulting in a noticeable speed-up factor. We present a new strategy of reuse of paths, which will allow us, given a previously computed set of radiosity solutions corresponding to n light positions, to add new light positions and accurately compute the radiosity solution at a reduced cost by reusing paths Our incremental strategy can be applied to light positioning in interior design, allowing the set of authorized light locations to be enriched by adding new positions chosen by the user.

The Spanish Kidney Exchange Model: Study of Computation-Based Alternatives to the Current Procedure

The problem of incompatible pairs in living-donor kidney transplant can be solved using paired kidney exchange, i.e., two incompatible patient-donor pairs interchange donors, creating a cycle, which can be extended to three or even more pairs. Finding a set of cycles that maximizes the number of successful transplants is a complex task.