Jorge Stolfi - Academia.edu (original) (raw)
Papers by Jorge Stolfi
... journals, and in our research report series. We will seek users for our prototype systems amo... more ... journals, and in our research report series. We will seek users for our prototype systems among those with whom we have common research interests, and we will encourage collaboration with university researchers. Robert W. Taylor, Director Page 3. Ruler, Compass, and ...
Computing Research Repository, 1998
We develop a class of new,kinetic data structures for collision detection between moving,convex p... more We develop a class of new,kinetic data structures for collision detection between moving,convex polytopes; the performance of these structures is sensitive to the separation of the polytopes during their motion. For two convex polygons in the plane, let D be the maximum diameter of the polygons, and let s be the minimum distance between them during their motion.,Our separation
Point location, often known in graphics as &a... more Point location, often known in graphics as "hit detection," is one of the fundamental problems of computational geometry. In a point location query we want to identify which of a given collection of geometric objects contains a particular point. Let denote a subdivision of the Euclidean plane into monotone regions by a straight-line graph of edges. In this paper we
We describe a general method for fitting 3D models of deformable biological structures to microsc... more We describe a general method for fitting 3D models of deformable biological structures to microscope images. The method uses multiscale image matching techniques with gradual introduction of parameters as well as specialized image synthesis methods and image distance metrics.
Electronic Notes in Discrete Mathematics
The non planar vertex deletion vd(G), of a graph G is the smallest positive integer k, such that ... more The non planar vertex deletion vd(G), of a graph G is the smallest positive integer k, such that the removal of k vertices from G produces a planar graph. We solve a problem proposed by Yannakakis: find the threshold for the maximum degree of a graph G such that, given a graph G and a positive integer k, to decide whether vd(G)≤k is NP-complete. We prove that it is NP-complete to decide whether a maximum degree 3 graph G and a positive integer k satisfy vd(G)≤k. We prove that to compute vd(G) is Max SNP-hard when restricted to a cubic input G. We exhibit a polynomial -approximation algorithm for finding a maximum planar induced subgraph of a maximum degree 3 graph.
1 – lucas.batista.freitas@gmail.com 2 – stolfi@ic.unicamp.br 3 – tygel@ime.unicamp.br We describe... more 1 – lucas.batista.freitas@gmail.com 2 – stolfi@ic.unicamp.br 3 – tygel@ime.unicamp.br We describe a fast method for seismic ray tracing in a cellular model, in which cells can have general polynomial shapes with non-planar bounding faces. The key idea is integration of the ray equations in terms of local cell coordinates rather than spatial coordinates. This approach allows for efficient detection of cell boundary crossing events, suppressing the need for costly non-linear equation solvers in the inner loop. cellular model, ray tracing, bezier blocks 1 – INTRODUCTION Seismic simulation is a powerful tool for a number of studies on seismic modeling, imaging and inversion for exploration and monitoring of oil reservoirs. These include, among others, planning of acquisition surveys, image interpretation through identification of key reflections, discrimination of primaries and multiples and amplitude analysis (AVO and AVA). Among various simulation techniques, ray tracing Cervený (2001...
ABSTRACT Shape deformation methods are important in such fields as geometric modeling and compute... more ABSTRACT Shape deformation methods are important in such fields as geometric modeling and computer animation. In biology, modeling of shape, growth, movement and pathologies of living microscopic organisms or cells require smooth deformations, which are essentially 2D with little change in depth. In this paper, we present a 2.5D space deformation method. The 3D model is modified by deforming an enclosing control grid of prisms. Spline interpolation is used to satisfy the smoothness requirement. We implemented this method in an editor which makes it possible to define and modify the deformation with the mouse in a user-friendly way. The experimental results show that the method is simple and effective.
We address the problem of efficient simulation of multiphaseflow in porous media — in particular,... more We address the problem of efficient simulation of multiphaseflow in porous media — in particular, flow in natural oil reservoirs under advancedexploitation regimes such as water injection. We use a finite-element approach on a dynamic adaptivedyadic grid - a hierarchic mesh where a cell at level is partitioned into two equal children at level by a hyperplane perpendicular to coordinate
Processing of the Portuguese Language, 2003
Abstract: We describe an ongoing project whose aim is to build a parserfor Brazilian Portuguese, ... more Abstract: We describe an ongoing project whose aim is to build a parserfor Brazilian Portuguese, Selva, which can be used as a basis for subsequentresearch in natural language processing, such as automatic translationand ellipsis and anaphora resolution. The parser is meant to handlearbitrary prose texts in unrestricted domains, including the full rangeof coordination and subordination constructs. The parser operates separatelyon
Computers & Graphics, 2014
We present a spatially and geometrically adaptive method for computing a robust polygonal approxi... more We present a spatially and geometrically adaptive method for computing a robust polygonal approximation of an implicit curve defined on a planar region or on a triangulated surface. Our method uses affine arithmetic to identify regions where the curve lies inside a thin strip. Unlike other interval methods, even those based on affine arithmetic, our method works on both rectangular
2009 16th International Conference on Systems, Signals and Image Processing, 2009
Abstract We propose a fast and robust approach to track deformable and rigid objects from a stati... more Abstract We propose a fast and robust approach to track deformable and rigid objects from a stationary/moving camera. The method combines seed estimation by the Kanade-Lucas-Tomasi (KLT) algorithm with object delineation by the image foresting transform to segment the object along the frames. The segmentation does not need to be perfect and it considerably improves efficiency and robustness in the KLT algorithm. The tests in real videos demonstrate good results, by outperforming two other KLT-based methods, in the ...
(EN) We describe an ongoing,research project on efficient methods,for identification and reconstr... more (EN) We describe an ongoing,research project on efficient methods,for identification and reconstruction of broken objects among,large collections of irregular fragments. Applications include archaeology, art restoration, failure analysis, and other disciplines. Our solution for flat objects uses multi-scale matching,and constrained dynamic,programming.,We are now extending it to curved pottery fragments through computational stereo vision techniques. Keywords: Digital reconstruction, multi-scale matching, pottery
Lecture Notes in Computer Science, 2011
We describe a fast and robust gradient integration method that computes scene depths (or heights)... more We describe a fast and robust gradient integration method that computes scene depths (or heights) from surface gradient (or surface normal) data such as would be obtained by photometric stereo or interferometry. Our method allows for uncertain or missing samples, ...
2008 XXI Brazilian Symposium on Computer Graphics and Image Processing, 2008
XX Brazilian Symposium on Computer Graphics and Image Processing (SIBGRAPI 2007), 2007
Procedings of the British Machine Vision Conference 2000, 2000
2011 18th IEEE International Conference on Image Processing, 2011
... journals, and in our research report series. We will seek users for our prototype systems amo... more ... journals, and in our research report series. We will seek users for our prototype systems among those with whom we have common research interests, and we will encourage collaboration with university researchers. Robert W. Taylor, Director Page 3. Ruler, Compass, and ...
Computing Research Repository, 1998
We develop a class of new,kinetic data structures for collision detection between moving,convex p... more We develop a class of new,kinetic data structures for collision detection between moving,convex polytopes; the performance of these structures is sensitive to the separation of the polytopes during their motion. For two convex polygons in the plane, let D be the maximum diameter of the polygons, and let s be the minimum distance between them during their motion.,Our separation
Point location, often known in graphics as &a... more Point location, often known in graphics as "hit detection," is one of the fundamental problems of computational geometry. In a point location query we want to identify which of a given collection of geometric objects contains a particular point. Let denote a subdivision of the Euclidean plane into monotone regions by a straight-line graph of edges. In this paper we
We describe a general method for fitting 3D models of deformable biological structures to microsc... more We describe a general method for fitting 3D models of deformable biological structures to microscope images. The method uses multiscale image matching techniques with gradual introduction of parameters as well as specialized image synthesis methods and image distance metrics.
Electronic Notes in Discrete Mathematics
The non planar vertex deletion vd(G), of a graph G is the smallest positive integer k, such that ... more The non planar vertex deletion vd(G), of a graph G is the smallest positive integer k, such that the removal of k vertices from G produces a planar graph. We solve a problem proposed by Yannakakis: find the threshold for the maximum degree of a graph G such that, given a graph G and a positive integer k, to decide whether vd(G)≤k is NP-complete. We prove that it is NP-complete to decide whether a maximum degree 3 graph G and a positive integer k satisfy vd(G)≤k. We prove that to compute vd(G) is Max SNP-hard when restricted to a cubic input G. We exhibit a polynomial -approximation algorithm for finding a maximum planar induced subgraph of a maximum degree 3 graph.
1 – lucas.batista.freitas@gmail.com 2 – stolfi@ic.unicamp.br 3 – tygel@ime.unicamp.br We describe... more 1 – lucas.batista.freitas@gmail.com 2 – stolfi@ic.unicamp.br 3 – tygel@ime.unicamp.br We describe a fast method for seismic ray tracing in a cellular model, in which cells can have general polynomial shapes with non-planar bounding faces. The key idea is integration of the ray equations in terms of local cell coordinates rather than spatial coordinates. This approach allows for efficient detection of cell boundary crossing events, suppressing the need for costly non-linear equation solvers in the inner loop. cellular model, ray tracing, bezier blocks 1 – INTRODUCTION Seismic simulation is a powerful tool for a number of studies on seismic modeling, imaging and inversion for exploration and monitoring of oil reservoirs. These include, among others, planning of acquisition surveys, image interpretation through identification of key reflections, discrimination of primaries and multiples and amplitude analysis (AVO and AVA). Among various simulation techniques, ray tracing Cervený (2001...
ABSTRACT Shape deformation methods are important in such fields as geometric modeling and compute... more ABSTRACT Shape deformation methods are important in such fields as geometric modeling and computer animation. In biology, modeling of shape, growth, movement and pathologies of living microscopic organisms or cells require smooth deformations, which are essentially 2D with little change in depth. In this paper, we present a 2.5D space deformation method. The 3D model is modified by deforming an enclosing control grid of prisms. Spline interpolation is used to satisfy the smoothness requirement. We implemented this method in an editor which makes it possible to define and modify the deformation with the mouse in a user-friendly way. The experimental results show that the method is simple and effective.
We address the problem of efficient simulation of multiphaseflow in porous media — in particular,... more We address the problem of efficient simulation of multiphaseflow in porous media — in particular, flow in natural oil reservoirs under advancedexploitation regimes such as water injection. We use a finite-element approach on a dynamic adaptivedyadic grid - a hierarchic mesh where a cell at level is partitioned into two equal children at level by a hyperplane perpendicular to coordinate
Processing of the Portuguese Language, 2003
Abstract: We describe an ongoing project whose aim is to build a parserfor Brazilian Portuguese, ... more Abstract: We describe an ongoing project whose aim is to build a parserfor Brazilian Portuguese, Selva, which can be used as a basis for subsequentresearch in natural language processing, such as automatic translationand ellipsis and anaphora resolution. The parser is meant to handlearbitrary prose texts in unrestricted domains, including the full rangeof coordination and subordination constructs. The parser operates separatelyon
Computers & Graphics, 2014
We present a spatially and geometrically adaptive method for computing a robust polygonal approxi... more We present a spatially and geometrically adaptive method for computing a robust polygonal approximation of an implicit curve defined on a planar region or on a triangulated surface. Our method uses affine arithmetic to identify regions where the curve lies inside a thin strip. Unlike other interval methods, even those based on affine arithmetic, our method works on both rectangular
2009 16th International Conference on Systems, Signals and Image Processing, 2009
Abstract We propose a fast and robust approach to track deformable and rigid objects from a stati... more Abstract We propose a fast and robust approach to track deformable and rigid objects from a stationary/moving camera. The method combines seed estimation by the Kanade-Lucas-Tomasi (KLT) algorithm with object delineation by the image foresting transform to segment the object along the frames. The segmentation does not need to be perfect and it considerably improves efficiency and robustness in the KLT algorithm. The tests in real videos demonstrate good results, by outperforming two other KLT-based methods, in the ...
(EN) We describe an ongoing,research project on efficient methods,for identification and reconstr... more (EN) We describe an ongoing,research project on efficient methods,for identification and reconstruction of broken objects among,large collections of irregular fragments. Applications include archaeology, art restoration, failure analysis, and other disciplines. Our solution for flat objects uses multi-scale matching,and constrained dynamic,programming.,We are now extending it to curved pottery fragments through computational stereo vision techniques. Keywords: Digital reconstruction, multi-scale matching, pottery
Lecture Notes in Computer Science, 2011
We describe a fast and robust gradient integration method that computes scene depths (or heights)... more We describe a fast and robust gradient integration method that computes scene depths (or heights) from surface gradient (or surface normal) data such as would be obtained by photometric stereo or interferometry. Our method allows for uncertain or missing samples, ...
2008 XXI Brazilian Symposium on Computer Graphics and Image Processing, 2008
XX Brazilian Symposium on Computer Graphics and Image Processing (SIBGRAPI 2007), 2007
Procedings of the British Machine Vision Conference 2000, 2000
2011 18th IEEE International Conference on Image Processing, 2011