Luís Paulo Santos - Publications

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Editor


Journal of Parallel Computing Volume 33, Issue 6, pags. 359-466 Parallel Graphics and Visualization Eds.: Luis Paulo Santos, Alan Heirich, Bruno Raffin June, 2007	Computers & Graphics Volume 32, Issue 1 Parallel Graphics and Visualization Eds.:Luis Paulo Santos, Dirk Reiners, Jean Favre March, 2008 (Guest Editorial - pp. 1-2)
Computers & Graphics Vol. 34, Issue 6 Graphics for Serious Games Eds.: Kurt Debattista, Alberto José Proença, Luís Paulo Santos December, 2010 http://dx.doi.org/10.1016/j.cag.2010.09.016
Computers & Graphics Volume 35, Issues 2 and 4 Special section on Cultural Heritage Eds.: Alan Chalmers, Mark Mudge, Luis Paulo Santos April and November, 2011 (special section link)


"Parallel Graphics and Visualization 2006 Eurographics/ACM Symposium Proceedings" Eds.: Alan Heirich, Bruno Raffin, Luis Paulo Santos May, 2006	"Parallel Graphics and Visualization 2007 Eurographics/ACM Symposium Proceedings" Eds.: Jean Favre, Luis Paulo Santos, Dirk Reiners May, 2007

List of Papers

2011

Jounals

Ferreira, V.; Santos, L.P.; Franzen, M.; Ghouati, O.O.; Simoes, R.;

“Estimating Local Part Thickness in Midplane Meshes for Finite Element Analysis”,

International Journal of Mathematics and Computers In Simulation, Volume 5, pp. 69 (2011)
(Link)

2010

Jounals

Debattista, Kurt and Dubla, Piotr and Santos, Luís Paulo and Chalmers, Alan;
"A Wait Free Shared-Memory Irradiance Caching";
IEEE Computer Graphics and Applications, vol 31(5), pp. 66-78, 2011
(Link)

International Conferences

Ferreira, Vânio and Santos, Luís Paulo and Simões, Ricardo and Franzen, Markus and Ghouati, Omar;
“Estimating Local Thickness for Finite Element Analysis”;
12th WSEAS International Conference on Mathematical and Computational Methods in Science and Engineering (MACMESE’2010);
Portugal, November, 2010

2009

Jounals

Debattista, Kurt and Dubla, Piotr and Banterle, Francesco and Santos, Luís Paulo and Chalmers, Alan;
"Instant Caching for Interactive Global Illumination";
Computer Graphics Forum, 28(8), pp. 2216-2228, December, 2009
(Link to the journal site)

International Conferences

Dubla, Piotr and Debattista, Kurt and Santos, Luís Paulo and Chalmers, Alan;
"Wait-Free Shared-Memory Irradiance Cache";
Eurographics Symposium on Parallel Graphics and Visualization (EGPGV’09), pp 57 - 64
Munich, Germany, March, 2009
(Link)

National Conferences

· Marques, Ricardo and Santos, Luís Paulo;
“GPU Ray Casting”
(artigo distinguido com menção honrosa pela Comissão Científica);
17º Encontro Português de Computação Gráfica;
Covilhã, Portugal, 2009

· Nunes, Miguel and Santos, Luís Paulo;
“Workload Distribution for Ray Tracing in Multi-Core Systems”;
17º Encontro Português de Computação Gráfica;
Covilhã, Portugal, 2009

2007

Jounals

Chalmers, Alan and Debattista, Kurt and Mastoropoulou, Georgia and Santos, Luís Paulo;
"There-Reality: Selective Rendering in High Fidelity Virtual Environments";
International Journal of Virtual Reality, Vol. 6(1), IPI Press, March, 2007
(Link to the journal site)

2006

International Conferences

	Chalmers, Alan and Debattista, Kurt and Santos, Luís Paulo; "Selectvive Rendering: Computing Only What You Can See"; Graphite'2006 - 4th Int. Conference on Computer Graphics and Interactive Techniques in Australasia and Southeast Asia - Keynote Paper; ACM SIGGRAPH; pp 9 - 18 Kuala Lumpur, Malaysia, 29 November -- 2 December, 2006 (Link to ACM Digital Library)
	Oliveira, António and Santos, Luís Paulo and Proença, Alberto; "Refinement Criteria for High Fidelity Interactive Walkthroughs"; Graphite'2006 - 4th Int. Conference on Computer Graphics and Interactive Techniques in Australasia and Southeast Asia; ACM SIGGRAPH; pp 453 - 460 Kuala Lumpur, Malaysia, 29 November -- 2 December, 2006 (PDF, 1841 KBytes) (Abstract) (Link to ACM Digital Library)
	Santos, Luís Paulo; "Interactive High Fidelity Navigation in Archaeological Models"; SIBGRAPI'2006 - Brazilian Symp. on Computer Graphics and Image Processing - Short paper Manaus, Brazil, 8 .. 11 October, 2006 (PDF, 398 KBytes) (Abstract )
	Debattista, Kurt and Santos, Luís Paulo and Chalmers, Alan; "Accelerating the Irradiance Cache through Parallel Component-Based Rendering"; EGPGV'2006 - 6th Eurographics Symposium on Parallel Graphics Visualization; In- cooperation with ACM SIGGRAPH Braga, Portugal, 11-12, May, 2006 (Abstract) (Link to Eurographics Digital Library)
	Santos, Luís Paulo and Valentim, Sérgio and Fernandes, António Ramires; "Parallel Progressive Precomputed Radiance Transfer"; SCCG'2006 - Spring Conference on Computer Graphics; In- cooperation with ACM SIGGRAPH and Eurographics Častá-Papiernička, Slovakia, 20-22, April, 2006 (Abstract) (Link to RepositoriUM)

2005

International Conferences

	Debattista, Kurt and Sundstedt, Veronica and Santos, Luís Paulo and Chalmers, Alan; "Selective Component Based Rendering"; Graphite'2005 - 3rd Int. Conference on Computer Graphics and Interactive Techniques in Australasia and Southeast Asia; ACM SIGGRAPH Dunedin, New Zealand, 29 November -- 2 December, 2005 (Abstract) (Link to ACM Digital Library)
	Santos, Luís Paulo and Coelho, Vítor and Bernardes, Paulo and Proença, Alberto; "High Fidelity Walkthroughs in Archaeology Sites"; VAST'2005 - 6th Int. Symposium on Virtual Reality, Archaeology and Cultural Heritage (short paper); Pisa, Italy, 9 -- 11 November, 2005 (PDF, 1022 KBytes)(Abstract)

National Conferences

2004

International Conferences

	Ledda, Patrick and Santos, Luis Paulo and Chalmers, Alan; "A Local Model of Eye Adaptation for High Dynamic Range Images"; Afrigraph'2004; Stellenbosch, Cape Town, South Africa; 3-5, November, 2004 (PDF, 3850 KBytes)(color plates: PDF, 3667 KBytes)(Abstract) (Link to ACM Digital Library)
	Santos, Luis Paulo and Proença, Alberto; "Scheduling Under Conditions of Uncertainty: a Bayesian Approach"; EuroPar'2004: Parallel Processing; Lecture Notes in Computer Science 3149; Springer-Verlag, pp 222-229; Pisa, Italy; 31 August - 3 September, 2004 (PDF, 138 KBytes)(Abstract) (Link to Springer OnLine)

2003

Technical Reports

Santos, Luis Paulo and Chalmers, Alan;
"Parallel Rendering with Radiance";
Technical Report; Dept. of Computer Science; University of Bristol; July, 2003
(PDF, 2152 KBytes)(Abstract) (see page)

2002

International Conferences

Santos, Luis Paulo and Proença, Alberto;
"A Systematic Approach to Effective Scheduling in Distributed Systems";
VECPAR'2002 - 5th Int. Meeting on High Performance Computing for Computational Science, pp. 813-825, Porto, Portugal, 26 - 28 June, 2002
(PDF, 182 KBytes)(Abstract)

2001

International Conferences

Santos, Luís Paulo and Proença, Alberto;
"A Bayesian RunTime Load Manager on a Shared Cluster";
Scheduling and Load Balancing on Clusters (SLAB'2001), special session in IEEE International Symposium on Cluster Computing and the Grid (CCGrid'2001), IEEE Computer Society Press,
Brisbane, Australia, 15--18 May, 2001
(PDF, 106 KBytes)(Abstract)
(Link to IEEE Digital Library)

1997

International Conferences

Cunha, Alcino and Santos, Luís Paulo and Belo, Orlando;
"Enhancing Load Distribution";
European Simulation Symposium 1997;
Passau, Germany, 1997
(Abstract)

Santos, Luís Paulo and Castro, Vítor and Proença, Alberto;
"Evaluation of the Communication Performance on a Parallel Processing System"
4th European PVM-MPI Users Group Meeting --- Recent Advances in Parallel Virtual Machine and Message Passing Interface;
Springer Lecture Notes in Computer Science 1332; ISBN 3-540-63697-8;
Krakow, Poland, 1997
(PDF, 172 KBytes)(Abstract)
(Link to Springer Online)

National Conferences

Cunha, Alcino and Santos, Luís Paulo and Belo, Orlando;
"Simulador de Estratégias de Distribuição de Carga";
3º Encontro Nacional do Colégio de Engenharia Electrotécnica, Ordem dos Engenheiros;
Matosinhos, Portugal, Junho, 1997

1994

International Conferences

Santos, Luís Paulo and Chalmers, Alan and Proença, Alberto
"A Messages Density Monitoring Strategy for Distributed Memory Parallel Systems";
2nd Int. Conf. on Software for Multiprocessors and SuperComputers, Theory, Practice, Experience (SMSTPE'94);
Moscow, Russia, September, 1994
(Abstract)

Abstracts

	Oliveira, António and Santos, Luís Paulo and Proença, Alberto; "Refinement Criteria for High Fidelity Interactive Walkthroughs"; Graphite'2006 - 4th Int. Conference on Computer Graphics and Interactive Techniques in Australasia and Southeast Asia; ACM SIGGRAPH Kuala Lumpur, Malaysia, 29 November -- 2 December, 2006 "Physically based global illumination rendering at interactive frame rates would enable users to navigate within complex virtual environments, such as archaeological models. These algorithms, however, are computationally too demanding to allow interactive navigation on current PCs. A technique based on image subsampling and spatiotemporal coherence among successive frames is exploited, while resorting to progressive refinement whenever there is available computing power. A physically based ray tracer (Radiance) is used to compute reflected radiance at the model’s triangles vertices. Progressive refinement is achieved increasing the sampling frequency by subdividing certain triangles and requesting shading information for the resulting vertices. This paper proposes and evaluates different criteria for selecting which triangles to subdivide. A random criterium and two criteria based on Normalized Luminance Differences are evaluated: one operating on image space, the other on object space. Results, obtained with a model of an old roman town, show that the object space criterium is able to locate and represent visual discontinuities, such as shadows, and does so requiring less triangle subdivisions than the other two."
	Santos, Luís Paulo; "Interactive High Fidelity Navigation in Archaeological Models"; SIBGRAPI'2006 - Brazilian Symp. on Computer Graphics and Image Processing - Short paper Manaus, Brazil, 8 .. 11 October, 2006 "Interactive navigation within virtual archaeological models using global illumination algorithms is a major challenge due to the huge computational requirements associated with these algorithms. We present a framework to achieve this goal, based on image space subsampling, parallel rendering, exploitation of spatiotemporal coherence and progressive refinement. Results, obtained with a prototype and a model of the roman town of Bracara Augusta, suggest that this is a promising approach."
	Debattista, Kurt and Santos, Luís Paulo and Chalmers, Alan; "Accelerating the Irradiance Cache through Parallel Component-Based Rendering"; EGPGV'2006 - 6th Eurographics Symposium on Parallel Graphics Visualization; In- cooperation with ACM SIGGRAPH Braga, Portugal, 11-12, May, 2006 "The irradiance cache is an acceleration data structure which caches indirect diffuse samples within the framework of a distributed ray-tracing algorithm. Previously calculated values can be stored and reused in future calculations, resulting in an order of magnitude improvement in computational performance. However, the irradiance cache is a shared data structure and so it is notoriously difficult to parallelise over a distributed parallel system. The hurdle to overcome is when and how to share cached samples. This sharing incurs communication overheads and yet must happen frequently to minimise cache misses and thus maximise the performance of the cache. We present a novel component-based parallel algorithm implemented on a cluster of computers, whereby the indirect diffuse calculations are calculated on a subset of nodes in the cluster. This method exploits the inherent spatial coherent nature of the irradiance cache; by reducing the set of nodes amongst which cached values must be shared, the sharing frequency can be kept high, thus decreasing both communication overheads and cache misses. We demonstrate how our new parallel rendering algorithm significantly outperforms traditional methods of distributing the irradiance cache."
	Santos, Luís Paulo and Valentim, Sérgio and Fernandes, António Ramires; "Parallel Progressive Precomputed Radiance Transfer"; SCCG'2006 - Spring Conference on Computer Graphics; In- cooperation with ACM SIGGRAPH and Eurographics Častá-Papiernička, Slovakia, 20-22, April, 2006 "Precomputed Radiance Transport (PRT) was introduced as a technique to enable interactive navigation and distant environmental real time relighting of rigid scenes. Evaluating radiance transport is, however, a computationally very demanding task, which precludes PRT's utilization during the model design phase, since the user must wait for long periods of time before being able to light and navigate within the model. This paper proposes and validates an approach to provide visual feedback to the user as soon as possible, within PRT context. By resorting to parallel processing and progressive refinement, the user is quickly presented with a lower lighting resolution of the virtual model. This is then progressively refined by incrementally increasing the number of incident directions taken into account on transport computations. PRT is, however, a complex algorithm that requires frequent collective communications of huge volumes of data, thus constraining the maximum achievable speedup on a parallel system. This issue is analysed and an alternative workload distribution is proposed and evaluated on a 12 node dual processor cluster. The final solution ensures a good resource utilization rate, reducing response times from dozens of seconds to a few hundred milliseconds."
	Debattista, Kurt and Sundstedt, Veronica and Santos, Luís Paulo and Chalmers, Alan; "Selective Component Based Rendering"; Graphite'2005 - 3rd Int. Conference on Computer Graphics and Interactive Techniques in Australasia and Southeast Asia; ACM SIGGRAPH Dunedin, New Zealand, 29 November -- 2 December, 2005 "The computational requirements of full global illumination rendering are such that it is still not possible to achieve high-fidelity graphics of very complex scenes in a reasonable time on a single computer. By identifying which computations are more relevant to the desired quality of the solution, selective rendering can significantly reduce rendering times. In this paper we present a novel component-based selective rendering system in which the quality of every image, and indeed every pixel, can be controlled by means of a component regular expression (crex). The crex provides a flexible mechanism for controlling which components are rendered and in which order. It can be used as a strategy for directing the light transport within a scene and also in a progressive rendering framework. Furthermore, the crex can be combined with visual perception techniques to reduce rendering computation times without compromising the perceived visual quality. By means of a psychophysical experiment we demonstrate how the crex can be successfully used in such a perceptual rendering framework. In addition, we show how the crex’s flexibility enables it to be incorporated in a predictive framework for time-constrained rendering." (Back to list of publications)

Santos, Luís Paulo and Coelho, Vítor and Bernardes, Paulo and Proença, Alberto;
"High Fidelity Walkthroughs in Archaeology Sites";
VAST'2005 - 6th Int. Symposium on Virtual Reality, Archaeology and Cultural Heritage (short
paper);
Pisa, Italy, 9 -- 11 November, 2005

"Fast and affordable computing systems currently support walkthroughs into virtual reconstructed sites, with fast frame rate generation of synthetic images. However, archaeologists still complain about the lack of realism in these interactive tours, mainly due to the false ambient illumination. Accurate visualizations require physically based global illumination models to render the scenes, which are computationally too demanding.

Faster systems and novel rendering techniques are required: current clusters provide a feasible and affordable path towards these goals, and we developed a framework to support smooth virtual walkthroughs, using progressive rendering to converge to high fidelity images whenever computing power surplus is available.

This framework exploits spatial and temporal coherence among successive frames, serving multiple clients that share and interact with the same virtual model, while maintaining each its own view of the model. It is based on a three-tier architecture: the outer layer embodies light-weight visualization clients, which perform all the user interactions and display the final images using the available graphics hardware; the inner layer is a parallel version of a physically based ray tracer running on a cluster of off-the-shelf PCs; in the middle layer lies the shading management agent (SMA), which monitors the clients' states, supplies each with properly shaded 3D points, maintains a cache of previously rendered geometry and requests relevant shading samples to the parallel renderer, whenever required.

A prototype of a high fidelity walkthrough in the archaeologic virtual model of the roman town of Bracara Augusta was developed, and the current evaluation tests aimed to measure the performance improvements due to the use of SMA caches and associated parallel rendering capabilities. Preliminary results show that interactive frame rates are sustainable and the system is highly responsive."

(Back to list of publications)

Sérgio R. MADEIRA, Luísa C. BASTOS, António M. SOUSA, João F. SOBRAL and Luís P. SANTOS;
"AUTOMATIC TRAFFIC SIGNS INVENTORY USING A MOBILE MAPPING SYSTEM";
GIS PLANET 2005, International Conference and Exhibition on Geographic Information;
Estoril, Lisboa, Portugal, 20 May - 2 June, 2005

"A Mobile Mapping System (MMS) designed to support quick surveys of traffic signs, including automatic sign recognition and exact location, is being developed in a partnership between Geonav, a private enterprise, and the University of Minho. The system acquisition is based on a road survey in a vehicle carrying digital video cameras, and a navigation system based in the integration of DGPS with an Inertial Measurement Unit and other dead reckoning systems. The acquisition system allows the association of a rigorous position and attitude to each digital frame. Furthermore, the pixel locations of every traffic sign visible in the video can be identified automatically through dedicated software, and their absolute geographical coordinates can be extracted. During the acquisition and processing stages, the relevant data is archived in a data base compatible with most CAD/SIG applications. Results of the tests carried out with this system show its effectiveness, with a good percentage of the traffic signs being automatically recognized and geo-referenced."

(Back to list of publications)

Ledda, Patrick and Santos, Luis Paulo and Chalmers, Alan;
"A Local Model of Eye Adaptation for High Dynamic Range Images";
Afrigraph'2004; Cape Town, South Africa; November, 2004

"In the real world, the human eye is confronted with a wide range of luminances from bright sunshine to low night light. Our eyes cope with this vast range of intensities by adaptation; changing their sensitivity to be responsive at different illumination levels. This adaptation is highly localized, allowing us to see both dark and bright regions of a high dynamic range environment. In this paper we present a new model of eye adaptation based on physiological data. The model, which can be easily integrated into existing renderers, can function either as a static local tone mapping operator for single high dynamic range image, or as a temporal adaptation model taking into account time elapsed and intensity of preadaptation for a dynamic sequence. We finally validate our technique with a high dynamic range display and a psychophysical study."

(Back to list of publications)

Santos, Luis Paulo and Proença, Alberto;
"Scheduling Under Conditions of Uncertainty: a Bayesian Approach";
EuroPar'2004; Lecture Notes in Computer Science; Springer-Verlag; Pisa, Italy; August, 2004

"The efficient execution of irregular parallel applications on shared distributed systems requires novel approaches to scheduling, since both the application requirements and the system resources exhibit an unpredictable behavior. This paper proposes Bayesian decision networks as the paradigm to handle the uncertainty a scheduler has about the environment's current and
future states. Experiments performed with a parallel ray tracer show promising performance improvements over a deterministic approach of identical complexity. These improvements grow as the level of system sharing and the application's workload irregularity increase, suggesting that the effectiveness of decision network based schedulers grows with the complexity of the
environment being managed."

(Back to list of publications)

	Santos, Luis Paulo and Chalmers, Alan; "Parallel Rendering with Radiance"; Technical Report; Dept. of Computer Science; University of Bristol; July, 2003 (see page) "Interactive global illumination at interactive rates is still an unachieved goal for medium to large complexity scenes and high fidelity illumination models, such as the one used by Radiance. In order to achieve this goal several different optimization approaches must be exploited, including parallelism, perceptual issues and low level optimizations. This work concentrates on developing a parallel message passing prototype of Radiance's renderer targeted towards producing animations. This prototype is used to study scalability issues and perceptual optimizations that will reduce rendering times and will, hopefully, be unnoticed by the viewer. The preliminary results obtained suggest that efforts should concentrate on reducing idle times due to suboptimal load distribution and indirect irradiance calculation times. Also psychophysical experiments and perceptual metrics should be carried on, in order to assess the impact of selective rendering on perceived quality." (Back to list of publications)
	Santos, Luis Paulo and Proença, Alberto; "A Systematic Approach to Effective Scheduling in Distributed Systems"; VECPAR'2002 - 5th Int. Meeting on High Performance Computing for Computational Science, Porto, Portugal, 26 - 28 June, 2002 "The main role of a scheduler on a distributed environment is to effectively and efficiently manage the code and data workload distribution. The scheduling context is presented to identify its main components and their role. To analyse the structure of a generic scheduler three main features are identified and further detailed: the performance model (effectiveness, environment and scheduling overheads metrics), the internal execution model and the decision making mechanism. Deterministic and stochastic approaches are discussed; the effectiveness of stochastic approaches increases with the environment uncertainties, both due to the system and the workload behaviours. A generic structure, based on Bayesian decision networks, for scheduling under conditions of uncertainty is proposed and some results are briefly presented; to overcome some drawbacks -- assessing initial estimates and eager approach to problem solving -- reinforcement learning is suggested as a research topic worth pursuing." (Back to list of publications)
	Santos, Luís Paulo and Proença, Alberto; "A Bayesian RunTime Load Manager on a Shared Cluster"; Scheduling and Load Balancing on Clusters (SLAB'2001), special session in IEEE International Symposium on Cluster Computing and the Grid (CCGrid'2001), IEEE Computer Society Press, Brisbane, Australia, 15--18 May, 2001 "The efficient execution of irregular data parallel applications, on dynamically shared computing clusters, requires novel approaches to manage the runtime load distribution. Such environments have an unpredictable dynamic behaviour, both due to the application requirements and to the available system's resources. This uncertainty was the main motivation to propose and evaluate an application level scheduler, where decisions are efficiently taken with improved accurate predictions on the environment's current and near future state, based on available incomplete and aged measured data. Bayesian decision networks are used as the scheduler's decision making mechanism; its effectiveness to manage the load distribution of a parallel ray tracer is assessed and compared with alternative strategies. The evaluation results, with complex scenes on a 7 shared nodes cluster with dynamically variable workloads, show considerable performance improvements over blind strategies, and stress the benefits over a sensor based deterministic approach of identical complexity." (Back to list of publications)
	Cunha, Alcino and Santos, Luís Paulo and Belo, Orlando; "Enhancing Load Distribution"; European Simulation Symposium 1997; Passau, Germany, 1997 Not available. (Back to list of publications)
	Santos, Luís Paulo and Castro, Vítor and Proença, Alberto; "Evaluation of the Communication Performance on a Parallel Processing System" 4th European PVM-MPI Users Group Meeting --- Recent Advances in Parallel Virtual Machine and Message Passing Interface; Springer Lecture Notes in Computer Science 1332; ISBN 3-540-63697-8; Krakow, Poland, 1997 "This article presents an evaluation study of point-to-point and collective communication performance on a parallel processing system, a 16 node Parsytec PowerXplorer, using three different communication environments: PARIX, PVM and MPI." (Back to list of publications)
	Santos, Luís Paulo and Chalmers, Alan and Proença, Alberto "A Messages Density Monitoring Strategy for Distributed Memory Parallel Systems"; 2nd Int. Conf. on Software for Multiprocessors and SuperComputers, Theory, Practice, Experience (SMSTPE'94); Moscow, Russia, September, 1994 "Complex applications on distributed memory parallel systems often follow a demand driven approach with domain decomposition. An uniform data distribution among the local memories at the processing elements, may require frequent remote data access. To keep the processors busy while data is remotely fetched, concurrent application processes are assigned to each transputer based processing element. Adding more concurrent application processes in a large scale parallel system may degrade performance, due to the traffic increase with data requests and data block replies. A conditional broadcast mechanism is implemented during data requests, to limit this flow of messages. Monitoring strategies are proposed to further reduce the messages density, and a parameterized model to measure and evaluate global execution times is presented." (Back to list of publications)