Reports de recerca
http://hdl.handle.net/2117/3297
2017-04-26T21:42:53Zh-graphs: A new representation for tree decompositions of graphs
http://hdl.handle.net/2117/99483
h-graphs: A new representation for tree decompositions of graphs
Hidalgo Garcia, Marta; Joan Arinyo, Robert
In geometric constraint solving, well constrained geometric problems can be abstracted as Laman graphs. If the graph is tree decomposable, the constraint-based geometric problem can be solved by a Decomposition-Recombination planner based solver. In general decomposition and recombination steps can be completed only when other steps have already been completed. This fact naturally defines a hierarchy in the decomposition-recombination steps that traditional tree decomposition representations do not capture explicitly. In this work we introduce h-graphs, a new representation for decompositions of tree decomposable Laman graphs, which captures dependence relations between different tree decomposition steps. We show how h-graphs help in efficiently computing parameter ranges for which solution instances to well constrained, tree decomposable geometric constraint problems with one degree of freedom can actually be constructed.
2017-01-17T13:41:49ZHidalgo Garcia, MartaJoan Arinyo, RobertIn geometric constraint solving, well constrained geometric problems can be abstracted as Laman graphs. If the graph is tree decomposable, the constraint-based geometric problem can be solved by a Decomposition-Recombination planner based solver. In general decomposition and recombination steps can be completed only when other steps have already been completed. This fact naturally defines a hierarchy in the decomposition-recombination steps that traditional tree decomposition representations do not capture explicitly. In this work we introduce h-graphs, a new representation for decompositions of tree decomposable Laman graphs, which captures dependence relations between different tree decomposition steps. We show how h-graphs help in efficiently computing parameter ranges for which solution instances to well constrained, tree decomposable geometric constraint problems with one degree of freedom can actually be constructed.On tree decomposability of Henneberg graphs
http://hdl.handle.net/2117/99452
On tree decomposability of Henneberg graphs
Hidalgo, Marta R.; Joan Arinyo, Robert
In this work we describe an algorithm that generates well constrained geometric constraint graphs which are solvable by the tree-decomposition constructive technique. The algorithm is based on Henneberg constructions and would be of help in transforming underconstrained problems into well constrained problems as well as in exploring alternative constructions over a given set of geometric elements.
2017-01-17T12:40:22ZHidalgo, Marta R.Joan Arinyo, RobertIn this work we describe an algorithm that generates well constrained geometric constraint graphs which are solvable by the tree-decomposition constructive technique. The algorithm is based on Henneberg constructions and would be of help in transforming underconstrained problems into well constrained problems as well as in exploring alternative constructions over a given set of geometric elements.Orientation, sphericity and roundness evaluation of particles using alternative 3D representations
http://hdl.handle.net/2117/99446
Orientation, sphericity and roundness evaluation of particles using alternative 3D representations
Cruz Matías, Irving; Ayala Vallespí, M. Dolors
Sphericity and roundness indices have been used mainly in geology to analyze the shape of particles. In this paper, geometric methods are proposed as an alternative to evaluate the orientation, sphericity and roundness indices of 3D objects. In contrast to previous works based on digital images, which use the voxel model, we represent the particles with the Extreme Vertices Model, a very concise representation for binary volumes. We define the orientation with three mutually orthogonal unit vectors. Then, some sphericity indices based on length measurement of the three representative axes of the particle can be computed. In addition, we propose a ray-casting-like approach to evaluate a 3D roundness index. This method provides roundness measurements that are highly correlated with those provided by the Krumbein's chart and other previous approach. Finally, as an example we apply the presented methods to analyze the sphericity and roundness of a real silica nano dataset.
2017-01-17T12:25:33ZCruz Matías, IrvingAyala Vallespí, M. DolorsSphericity and roundness indices have been used mainly in geology to analyze the shape of particles. In this paper, geometric methods are proposed as an alternative to evaluate the orientation, sphericity and roundness indices of 3D objects. In contrast to previous works based on digital images, which use the voxel model, we represent the particles with the Extreme Vertices Model, a very concise representation for binary volumes. We define the orientation with three mutually orthogonal unit vectors. Then, some sphericity indices based on length measurement of the three representative axes of the particle can be computed. In addition, we propose a ray-casting-like approach to evaluate a 3D roundness index. This method provides roundness measurements that are highly correlated with those provided by the Krumbein's chart and other previous approach. Finally, as an example we apply the presented methods to analyze the sphericity and roundness of a real silica nano dataset.A practical and robust method to compute the boundary of three-dimensional axis-aligned boxes
http://hdl.handle.net/2117/99421
A practical and robust method to compute the boundary of three-dimensional axis-aligned boxes
López Monterde, Daniel; Martínez Bayona, Jonas; Vigo Anglada, Marc; Pla García, Núria
The union of axis-aligned boxes results in a constrained structure that is advantageous for solving certain geometrical problems. A widely used scheme for solid modelling systems is the boundary representation (Brep). We present a method to obtain the B-rep of a union of axis-aligned boxes. Our method computes all boundary vertices, and additional information for each vertex that allows us to apply already existing methods to extract the B-rep. It is based on dividing the three-dimensional problem into two-dimensional boundary computations and combining their results. The method can deal with all geometrical degeneracies that may arise. Experimental results prove that our approach outperforms existing general methods, both in efficiency and robustness.
2017-01-17T10:43:45ZLópez Monterde, DanielMartínez Bayona, JonasVigo Anglada, MarcPla García, NúriaThe union of axis-aligned boxes results in a constrained structure that is advantageous for solving certain geometrical problems. A widely used scheme for solid modelling systems is the boundary representation (Brep). We present a method to obtain the B-rep of a union of axis-aligned boxes. Our method computes all boundary vertices, and additional information for each vertex that allows us to apply already existing methods to extract the B-rep. It is based on dividing the three-dimensional problem into two-dimensional boundary computations and combining their results. The method can deal with all geometrical degeneracies that may arise. Experimental results prove that our approach outperforms existing general methods, both in efficiency and robustness.Back-to-front orderings of triangles in triangulated terrains over regular grids
http://hdl.handle.net/2117/99418
Back-to-front orderings of triangles in triangulated terrains over regular grids
Alonso Alonso, Jesús; Joan Arinyo, Robert
In this work we report on a complete and correct set of configurations to realistically rendering triangulated heightfields dedined over regular grids by visiting triangles in a back-to-front order. The experiments conducted show that a simple CPU-based implementation performs as well as an up-to-date native graphics card z-buffer and allows real time interaction when the vieweing position is fixed and when it moves along a 3D path.
2017-01-17T10:28:56ZAlonso Alonso, JesúsJoan Arinyo, RobertIn this work we report on a complete and correct set of configurations to realistically rendering triangulated heightfields dedined over regular grids by visiting triangles in a back-to-front order. The experiments conducted show that a simple CPU-based implementation performs as well as an up-to-date native graphics card z-buffer and allows real time interaction when the vieweing position is fixed and when it moves along a 3D path.Interaction techniques in virtual environments
http://hdl.handle.net/2117/99408
Interaction techniques in virtual environments
Moya Santos, Sergio; Grau, Sergi; Tost Pardell, Daniela
Virtual environments are used in very diverse applications: from leisure
games to professional training and rehabilitation systems. In these applications, users interact with the elements of the environments through avatars in order to perform virtually actions such as picking objects, carrying and dropping them, and more complex manipulations tasks such as cutting and drilling in surgery training, shooting and punching in actions games, and cooking and cleaning in life simulation games and neuropsychological rehabilitation. To launch these actions, users must first select the objects with which they want to interact by pointing on them and confirming the selection by clicking a button or a key. This process is usually defined as point-and-click and more shortly pointing.
Pointing is an essential feature of interaction in virtual environments, and it is relevant to measure its usability. Besides, pointing in 3D environments has a lot of similarities with pointing in 2D graphical interfaces. Fitts's law relates the efficacy of pointing with the distance to the target and the target's width. The efficacy is also affected by the density of the environment and its level of occlusion. The influence of these factors has been studied in various papers to propose different types of pointing mechanisms. In this report we classify and survey these techniques.
2017-01-17T09:57:55ZMoya Santos, SergioGrau, SergiTost Pardell, DanielaVirtual environments are used in very diverse applications: from leisure
games to professional training and rehabilitation systems. In these applications, users interact with the elements of the environments through avatars in order to perform virtually actions such as picking objects, carrying and dropping them, and more complex manipulations tasks such as cutting and drilling in surgery training, shooting and punching in actions games, and cooking and cleaning in life simulation games and neuropsychological rehabilitation. To launch these actions, users must first select the objects with which they want to interact by pointing on them and confirming the selection by clicking a button or a key. This process is usually defined as point-and-click and more shortly pointing.
Pointing is an essential feature of interaction in virtual environments, and it is relevant to measure its usability. Besides, pointing in 3D environments has a lot of similarities with pointing in 2D graphical interfaces. Fitts's law relates the efficacy of pointing with the distance to the target and the target's width. The efficacy is also affected by the density of the environment and its level of occlusion. The influence of these factors has been studied in various papers to propose different types of pointing mechanisms. In this report we classify and survey these techniques.Fast connected component labeling algorithm: a non voxel-based approach
http://hdl.handle.net/2117/97534
Fast connected component labeling algorithm: a non voxel-based approach
Ayala Vallespí, M. Dolors; Rodríguez, J; Aguilera, A
This paper presents a new approach to achieve connected component labeling on both binary images and volumes by using the Extreme Vertices Model (EVM), a representation model for orthogonal
polyhedra, applied to digital images and volume datasets recently. In contrast with previous techniques, this method does not use a voxel-based approach but deals with the inner sections of the object.
2016-11-30T15:03:40ZAyala Vallespí, M. DolorsRodríguez, JAguilera, AThis paper presents a new approach to achieve connected component labeling on both binary images and volumes by using the Extreme Vertices Model (EVM), a representation model for orthogonal
polyhedra, applied to digital images and volume datasets recently. In contrast with previous techniques, this method does not use a voxel-based approach but deals with the inner sections of the object.Two triangulations methods based on edge refinement
http://hdl.handle.net/2117/97379
Two triangulations methods based on edge refinement
Ayala Vallespí, M. Dolors; Pla García, Núria; Vigo Anglada, Marc
In this paper two curvature adaptive methods of surface triangulation
are presented. Both methods are based on edge refinement to obtain a
triangulation compatible with the curvature requirements. The first
method applies an incremental and constrained Delaunay triangulation
and uses curvature bounds to determine if an edge of the triangulation
is admissible. The second method uses this function also in the edge
refinement process, i.e. in the computation of the location of a
refining point, and in the re-triangulation needed after the insertion
of this refining point. Results are presented, comparing both
approaches
2016-11-29T09:08:23ZAyala Vallespí, M. DolorsPla García, NúriaVigo Anglada, MarcIn this paper two curvature adaptive methods of surface triangulation
are presented. Both methods are based on edge refinement to obtain a
triangulation compatible with the curvature requirements. The first
method applies an incremental and constrained Delaunay triangulation
and uses curvature bounds to determine if an edge of the triangulation
is admissible. The second method uses this function also in the edge
refinement process, i.e. in the computation of the location of a
refining point, and in the re-triangulation needed after the insertion
of this refining point. Results are presented, comparing both
approachesUna paral·lelització SIMD de la conversió d'objectes codificats segons el model de fronteres al model d'octrees clàssics
http://hdl.handle.net/2117/97300
Una paral·lelització SIMD de la conversió d'objectes codificats segons el model de fronteres al model d'octrees clàssics
Joan Arinyo, Robert; Solé, Jaume
In this work a new SIMD parallel algorithm to generate Classical Octrees from Boundary Representations is presented. The algorithm consists of two main steps. First all the grey terminal nodes in the final octree are determined and encoded in parallel. Then the whole tree is deduced in parallel from the codes determined in the first step in a bottom-top manner.
2016-11-28T10:38:37ZJoan Arinyo, RobertSolé, JaumeIn this work a new SIMD parallel algorithm to generate Classical Octrees from Boundary Representations is presented. The algorithm consists of two main steps. First all the grey terminal nodes in the final octree are determined and encoded in parallel. Then the whole tree is deduced in parallel from the codes determined in the first step in a bottom-top manner.Triangles, ruler, and compass
http://hdl.handle.net/2117/97297
Triangles, ruler, and compass
Joan Arinyo, Robert
A triangle can be specified by giving three independent geometric relationships between its elements. Usually, these relationships are distances between two vertices, angles between two sides, and heights. For each triangle specified by a set of three of such relationships, we present a procedure that constructs the triangle using ruler and compass alone.
2016-11-28T10:21:40ZJoan Arinyo, RobertA triangle can be specified by giving three independent geometric relationships between its elements. Usually, these relationships are distances between two vertices, angles between two sides, and heights. For each triangle specified by a set of three of such relationships, we present a procedure that constructs the triangle using ruler and compass alone.