Pedro J de Rezende | Universidade Estadual de Campinas (original) (raw)

Papers by Pedro J de Rezende

Computers & Operations Research, 2013

ABSTRACT Proportional symbol map is a cartographic tool that employs symbols to represent data as... more ABSTRACT Proportional symbol map is a cartographic tool that employs symbols to represent data associated with specific locations. Each symbol is drawn at the location of an event and its size is proportional to the numerical data collected at that point on the map. The symbols considered here are opaque disks. When two or more disks overlap, part of their boundaries may not be visible and it might be difficult to gauge their size. Therefore, the order in which the disks are drawn affects the visual quality of a map. In this work, we focus on stacking drawings, i.e., a drawing that corresponds to the disks being stacked up, in sequence, starting from the one at the bottom of the stack. We address the Max-Total problem, which consists in maximizing the total visible boundary of all disks. We propose a sophisticated heuristic based on GRASP that includes most of the advanced techniques described in the literature for this procedure. We tested both sequential and parallel implementations on benchmark instances and the comparison against optimal solutions confirms the high quality of our heuristic. To the best of our knowledge, this is the first time a metaheuristic is applied to this problem.

INFORMS Journal on Computing, 2014

2011 24th SIBGRAPI Conference on Graphics, Patterns and Images, 2011

Proportional symbol maps are an often used tool to aid cartographers and geo-science professional... more Proportional symbol maps are an often used tool to aid cartographers and geo-science professionals to visualize data associated with events (e.g., earthquakes) or geo-positioned statistical data (e.g., population). At specific locations, symbols are placed and scaled so that their areas become proportional to the magnitudes of the events or data. Recent work approaches the problem of drawing these symbols algorithmically and defines metrics to be optimized to attain different kinds of drawings. We focus specifically on optimizing the visualization of physically realizable drawings of opaque disks by maximizing the sum of the visible borders of such disks. As this problem has been proven to be NP-hard, we provide an integer programming model for its solution along with decomposition techniques designed to decrease the size of input instances. We present computational experiments to assess the performance of our model as well as the effectiveness of our decomposition techniques.

We present a geometric de nition of conic sections in the oriented projective plane and describe ... more We present a geometric de nition of conic sections in the oriented projective plane and describe some of their nice properties. The three main classes of a ne conics are uni ed by a generalized distance notion on that space. This de nition leads to a very simple representation of conic arcs suitable for implementations of geometric solutions to problems involving the concept of distance, in particular, the construction of various generalizations of Voronoi diagrams.

Computing shortest geodesic paths is a crucial problem in several application areas, including ro... more Computing shortest geodesic paths is a crucial problem in several application areas, including robotics, medical imaging, terrain navigation and computational geometry. This type of computation on triangular meshes helps to solve different tasks, such as mesh watermarking, shape classification and mesh parametrization. In this work, a priority queue based on a bucketing structure is applied to speed up graph-based methods that approximates shortest geodesic paths on polyhedra. Initially, the problem is stated, some of its properties are discussed and a review of relevant methods is presented. Finally, we describe the proposed method and show several results and comparisons that confirm its benefits.

The Art Gallery Problem is one of the most well-known problems in Computational Geometry, with a ... more The Art Gallery Problem is one of the most well-known problems in Computational Geometry, with a rich history in the study of algorithms, complexity, and variants. Recently there has been a surge in experimental work on the problem. In this survey, we describe this work, show the chronology of developments, and compare current algorithms, including two unpublished versions, in an exhaustive experiment. Furthermore, we show what core algorithmic ingredients have led to recent successes.

PLOS ONE, 2015

Nowadays, large datasets are common and demand faster and more effective pattern analysis techniq... more Nowadays, large datasets are common and demand faster and more effective pattern analysis techniques. However, methodologies to compare classifiers usually do not take into account the learning-time constraints required by applications. This work presents a methodology to compare classifiers with respect to their ability to learn from classification errors on a large learning set, within a given time limit. Faster techniques may acquire more training samples, but only when they are more effective will they achieve higher performance on unseen testing sets. We demonstrate this result using several techniques, multiple datasets, and typical learning-time limits required by applications.

Lecture Notes in Computer Science, 2015

Pattern Recognition, 2015

ABSTRACT We have developed an automated system for the diagnosis of intestinal parasites from opt... more ABSTRACT We have developed an automated system for the diagnosis of intestinal parasites from optical microscopy images. The objects (species of parasites and impurities) segmented from these images form a large dataset. We are interested in the active learning problem of selecting a reasonably small number of objects to be labeled under an expert's supervision for use in training a pattern classifier. However, impurities are very numerous, constitute several clusters in the feature space, and can be quite similar to some species of parasites, leading to a significant challenge for active learning methods. We propose a technique that pre-organizes the data and then properly balances the selection of samples from all classes and uncertain samples for training. Early data organization avoids reprocessing of the large dataset at each learning iteration, enabling the halting of sample selection after a desired number of samples per iteration, yielding interactive response time. We validate our method by comparing it with state-of-the-art approaches, using a previously labeled dataset of almost 6,000 objects. Moreover, we report results from experiments on a very realistic scenario, consisting of a dataset with over 140,000 unlabeled objects, under unbalanced classes, absence of some classes, and the presence of a very large set of impurities.

Proceedings X Brazilian Symposium on Computer Graphics and Image Processing, 1997

We present a geometric de nition of conic sections in the oriented projective plane and describe ... more We present a geometric de nition of conic sections in the oriented projective plane and describe some of their nice properties. This de nition leads to a very simple and unambiguous representation for a ne conics and conic arcs. A conic of any t ype is represented by the homogeneous coordinates of its foci and one point on it, hence, the metric plays a major role in this case as opposed to the traditional algebraic characterization of conics as second degree polynomial curves. This representation is particularly suitable for the implementation of geometric solutions of problems that involve the concept of distance. Furthermore, we discuss point location with respect to conic curves which constitutes an important elementary operation for the solution of many such problems.

Proceedings of the ninth annual symposium on Computational geometry - SCG '93, 1993

The accompanying videotape presents two animation modes provided by the Geometric Laboratory GeoL... more The accompanying videotape presents two animation modes provided by the Geometric Laboratory GeoLab which we have developed as a programming environment for implementation, testing and animation of geometric algorithsm. GeoLab runs on SparcStations under Sun/OS using the XView graphics library, following the OpenLook graphical user interface guidelines.

Proceedings of the 28th Annual ACM Symposium on Applied Computing - SAC '13, 2013

ABSTRACT The labor-intensive and time-consuming process of annotating data is a serious bottlenec... more ABSTRACT The labor-intensive and time-consuming process of annotating data is a serious bottleneck in many pattern recognition applications when handling massive datasets. Active learning strategies have been sought to reduce the cost on human annotation, by means of automatically selecting the most informative unlabeled samples for annotation. The critical issue lies on the selection of such samples. As an effective solution, we propose an active learning approach that preprocesses the dataset, efficiently reduces and organizes a learning set of samples and selects the most representative ones for human annotation. Experiments performed on real datasets show that the proposed approach requires only a few iterations to achieve high accuracy, keeping user involvement to a minimum.

Proceedings of the twenty-first annual symposium on Computational geometry - SCG '05, 2005

The oriented projective plane T 2 is an extension of the Euclidean plane E 2 and comprises a numb... more The oriented projective plane T 2 is an extension of the Euclidean plane E 2 and comprises a number of advantages for algorithm design and implementation. We have extended the Computational Geometry Algorithms Library (CGAL) to allow for the implementation of geometric primitives and algorithms. The present video illustrates both the extension of a few algorithms to T 2 under CGAL and a dynamic visualization system (T 2 Viewer) built specially for displaying the spherical and planar models of T 2 .

Multimedia Tools and Applications, 1999

In video-on-demand systems, users expect to watch a film right after its selection. Nonetheless, ... more In video-on-demand systems, users expect to watch a film right after its selection. Nonetheless, such a short response time is feasible only if there is available bandwidth. In line with that, several techniques have been proposed to reduce the huge bandwidth demand on video servers. In this paper, we introduce the Piggybacking policy S 2 , which adds a second level of optimization to the Snapshot policy. Moreover, we introduce a heuristic to reduce the complexity to generate the tree of superimposed video streams.

XII Brazilian Symposium on Computer Graphics and Image Processing (Cat. No.PR00481), 1999

We generalize to the oriented projective plane T2 an algorithm for constructing all order k Voron... more We generalize to the oriented projective plane T2 an algorithm for constructing all order k Voronoi diagrams in the Euclidean plane. We also show that, for fixed k and for a finite set of sites, an order k Voronoi diagram in T2 has an exact number of regions. Furthermore, we show that the order k Voronoi diagram of a set

2013 XXVI Conference on Graphics, Patterns and Images, 2013

ABSTRACT There are many scenarios in which user interaction is essential for effective image segm... more ABSTRACT There are many scenarios in which user interaction is essential for effective image segmentation. In this paper, we present a new interactive segmentation method based on the Image Foresting Transform (IFT). The method over segments the input image, creates a graph based on these segments (super pixels), receives markers (labels) drawn by the user on some super pixels and organizes a competition to label every pixel in the image. Our method has several interesting properties: it is effective, efficient, capable of segmenting multiple objects in almost linear time on the number of super pixels, readily extendable through previously published techniques, and benefits from domain-specific feature extraction. We also present a comparison with another technique based on the IFT, which can be seen as its pixel-based counterpart. Another contribution of this paper is the description of automatic (robot) users. Given a ground truth image, these robots simulate interactive segmentation by trained and untrained users, reducing the costs and biases involved in comparing segmentation techniques.

Advances in Geographic Information Science, 2012

Proceedings of the 29th annual symposium on Symposuim on computational geometry - SoCG '13, 2013

Lecture Notes in Computer Science, 2008

... The classical Art Gallery Problem originally posed by Victor Klee in 1973 con-sists in ... Re... more ... The classical Art Gallery Problem originally posed by Victor Klee in 1973 con-sists in ... Rezende, PJ: OAGPLIB - Orthogonal art gallery problem library, www.ic.unicamp.br/∼cid/Problem-instances ... In: Conejo, R., Urretavizcaya, M., Pérez-de-la-Cruz, J.-L. (eds.) CAEPIA/TTIA 2003. ...

Computers & Operations Research, 2013

ABSTRACT Proportional symbol map is a cartographic tool that employs symbols to represent data as... more ABSTRACT Proportional symbol map is a cartographic tool that employs symbols to represent data associated with specific locations. Each symbol is drawn at the location of an event and its size is proportional to the numerical data collected at that point on the map. The symbols considered here are opaque disks. When two or more disks overlap, part of their boundaries may not be visible and it might be difficult to gauge their size. Therefore, the order in which the disks are drawn affects the visual quality of a map. In this work, we focus on stacking drawings, i.e., a drawing that corresponds to the disks being stacked up, in sequence, starting from the one at the bottom of the stack. We address the Max-Total problem, which consists in maximizing the total visible boundary of all disks. We propose a sophisticated heuristic based on GRASP that includes most of the advanced techniques described in the literature for this procedure. We tested both sequential and parallel implementations on benchmark instances and the comparison against optimal solutions confirms the high quality of our heuristic. To the best of our knowledge, this is the first time a metaheuristic is applied to this problem.

INFORMS Journal on Computing, 2014

2011 24th SIBGRAPI Conference on Graphics, Patterns and Images, 2011

Proportional symbol maps are an often used tool to aid cartographers and geo-science professional... more Proportional symbol maps are an often used tool to aid cartographers and geo-science professionals to visualize data associated with events (e.g., earthquakes) or geo-positioned statistical data (e.g., population). At specific locations, symbols are placed and scaled so that their areas become proportional to the magnitudes of the events or data. Recent work approaches the problem of drawing these symbols algorithmically and defines metrics to be optimized to attain different kinds of drawings. We focus specifically on optimizing the visualization of physically realizable drawings of opaque disks by maximizing the sum of the visible borders of such disks. As this problem has been proven to be NP-hard, we provide an integer programming model for its solution along with decomposition techniques designed to decrease the size of input instances. We present computational experiments to assess the performance of our model as well as the effectiveness of our decomposition techniques.

We present a geometric de nition of conic sections in the oriented projective plane and describe ... more We present a geometric de nition of conic sections in the oriented projective plane and describe some of their nice properties. The three main classes of a ne conics are uni ed by a generalized distance notion on that space. This de nition leads to a very simple representation of conic arcs suitable for implementations of geometric solutions to problems involving the concept of distance, in particular, the construction of various generalizations of Voronoi diagrams.

Computing shortest geodesic paths is a crucial problem in several application areas, including ro... more Computing shortest geodesic paths is a crucial problem in several application areas, including robotics, medical imaging, terrain navigation and computational geometry. This type of computation on triangular meshes helps to solve different tasks, such as mesh watermarking, shape classification and mesh parametrization. In this work, a priority queue based on a bucketing structure is applied to speed up graph-based methods that approximates shortest geodesic paths on polyhedra. Initially, the problem is stated, some of its properties are discussed and a review of relevant methods is presented. Finally, we describe the proposed method and show several results and comparisons that confirm its benefits.

The Art Gallery Problem is one of the most well-known problems in Computational Geometry, with a ... more The Art Gallery Problem is one of the most well-known problems in Computational Geometry, with a rich history in the study of algorithms, complexity, and variants. Recently there has been a surge in experimental work on the problem. In this survey, we describe this work, show the chronology of developments, and compare current algorithms, including two unpublished versions, in an exhaustive experiment. Furthermore, we show what core algorithmic ingredients have led to recent successes.

PLOS ONE, 2015

Nowadays, large datasets are common and demand faster and more effective pattern analysis techniq... more Nowadays, large datasets are common and demand faster and more effective pattern analysis techniques. However, methodologies to compare classifiers usually do not take into account the learning-time constraints required by applications. This work presents a methodology to compare classifiers with respect to their ability to learn from classification errors on a large learning set, within a given time limit. Faster techniques may acquire more training samples, but only when they are more effective will they achieve higher performance on unseen testing sets. We demonstrate this result using several techniques, multiple datasets, and typical learning-time limits required by applications.

Lecture Notes in Computer Science, 2015

Pattern Recognition, 2015

ABSTRACT We have developed an automated system for the diagnosis of intestinal parasites from opt... more ABSTRACT We have developed an automated system for the diagnosis of intestinal parasites from optical microscopy images. The objects (species of parasites and impurities) segmented from these images form a large dataset. We are interested in the active learning problem of selecting a reasonably small number of objects to be labeled under an expert's supervision for use in training a pattern classifier. However, impurities are very numerous, constitute several clusters in the feature space, and can be quite similar to some species of parasites, leading to a significant challenge for active learning methods. We propose a technique that pre-organizes the data and then properly balances the selection of samples from all classes and uncertain samples for training. Early data organization avoids reprocessing of the large dataset at each learning iteration, enabling the halting of sample selection after a desired number of samples per iteration, yielding interactive response time. We validate our method by comparing it with state-of-the-art approaches, using a previously labeled dataset of almost 6,000 objects. Moreover, we report results from experiments on a very realistic scenario, consisting of a dataset with over 140,000 unlabeled objects, under unbalanced classes, absence of some classes, and the presence of a very large set of impurities.

Proceedings X Brazilian Symposium on Computer Graphics and Image Processing, 1997

We present a geometric de nition of conic sections in the oriented projective plane and describe ... more We present a geometric de nition of conic sections in the oriented projective plane and describe some of their nice properties. This de nition leads to a very simple and unambiguous representation for a ne conics and conic arcs. A conic of any t ype is represented by the homogeneous coordinates of its foci and one point on it, hence, the metric plays a major role in this case as opposed to the traditional algebraic characterization of conics as second degree polynomial curves. This representation is particularly suitable for the implementation of geometric solutions of problems that involve the concept of distance. Furthermore, we discuss point location with respect to conic curves which constitutes an important elementary operation for the solution of many such problems.

Proceedings of the ninth annual symposium on Computational geometry - SCG '93, 1993

The accompanying videotape presents two animation modes provided by the Geometric Laboratory GeoL... more The accompanying videotape presents two animation modes provided by the Geometric Laboratory GeoLab which we have developed as a programming environment for implementation, testing and animation of geometric algorithsm. GeoLab runs on SparcStations under Sun/OS using the XView graphics library, following the OpenLook graphical user interface guidelines.

Proceedings of the 28th Annual ACM Symposium on Applied Computing - SAC '13, 2013

ABSTRACT The labor-intensive and time-consuming process of annotating data is a serious bottlenec... more ABSTRACT The labor-intensive and time-consuming process of annotating data is a serious bottleneck in many pattern recognition applications when handling massive datasets. Active learning strategies have been sought to reduce the cost on human annotation, by means of automatically selecting the most informative unlabeled samples for annotation. The critical issue lies on the selection of such samples. As an effective solution, we propose an active learning approach that preprocesses the dataset, efficiently reduces and organizes a learning set of samples and selects the most representative ones for human annotation. Experiments performed on real datasets show that the proposed approach requires only a few iterations to achieve high accuracy, keeping user involvement to a minimum.

Proceedings of the twenty-first annual symposium on Computational geometry - SCG '05, 2005

The oriented projective plane T 2 is an extension of the Euclidean plane E 2 and comprises a numb... more The oriented projective plane T 2 is an extension of the Euclidean plane E 2 and comprises a number of advantages for algorithm design and implementation. We have extended the Computational Geometry Algorithms Library (CGAL) to allow for the implementation of geometric primitives and algorithms. The present video illustrates both the extension of a few algorithms to T 2 under CGAL and a dynamic visualization system (T 2 Viewer) built specially for displaying the spherical and planar models of T 2 .

Multimedia Tools and Applications, 1999

In video-on-demand systems, users expect to watch a film right after its selection. Nonetheless, ... more In video-on-demand systems, users expect to watch a film right after its selection. Nonetheless, such a short response time is feasible only if there is available bandwidth. In line with that, several techniques have been proposed to reduce the huge bandwidth demand on video servers. In this paper, we introduce the Piggybacking policy S 2 , which adds a second level of optimization to the Snapshot policy. Moreover, we introduce a heuristic to reduce the complexity to generate the tree of superimposed video streams.

XII Brazilian Symposium on Computer Graphics and Image Processing (Cat. No.PR00481), 1999

We generalize to the oriented projective plane T2 an algorithm for constructing all order k Voron... more We generalize to the oriented projective plane T2 an algorithm for constructing all order k Voronoi diagrams in the Euclidean plane. We also show that, for fixed k and for a finite set of sites, an order k Voronoi diagram in T2 has an exact number of regions. Furthermore, we show that the order k Voronoi diagram of a set

2013 XXVI Conference on Graphics, Patterns and Images, 2013

ABSTRACT There are many scenarios in which user interaction is essential for effective image segm... more ABSTRACT There are many scenarios in which user interaction is essential for effective image segmentation. In this paper, we present a new interactive segmentation method based on the Image Foresting Transform (IFT). The method over segments the input image, creates a graph based on these segments (super pixels), receives markers (labels) drawn by the user on some super pixels and organizes a competition to label every pixel in the image. Our method has several interesting properties: it is effective, efficient, capable of segmenting multiple objects in almost linear time on the number of super pixels, readily extendable through previously published techniques, and benefits from domain-specific feature extraction. We also present a comparison with another technique based on the IFT, which can be seen as its pixel-based counterpart. Another contribution of this paper is the description of automatic (robot) users. Given a ground truth image, these robots simulate interactive segmentation by trained and untrained users, reducing the costs and biases involved in comparing segmentation techniques.

Advances in Geographic Information Science, 2012

Proceedings of the 29th annual symposium on Symposuim on computational geometry - SoCG '13, 2013

Lecture Notes in Computer Science, 2008

... The classical Art Gallery Problem originally posed by Victor Klee in 1973 con-sists in ... Re... more ... The classical Art Gallery Problem originally posed by Victor Klee in 1973 con-sists in ... Rezende, PJ: OAGPLIB - Orthogonal art gallery problem library, www.ic.unicamp.br/∼cid/Problem-instances ... In: Conejo, R., Urretavizcaya, M., Pérez-de-la-Cruz, J.-L. (eds.) CAEPIA/TTIA 2003. ...