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232
Cortical surfacebased analysis II: Inflation, flattening, and a surfacebased coordinate system
 NEUROIMAGE
, 1999
"... The surface of the human cerebral cortex is a highly folded sheet with the majority of its surface area buried within folds. As such, it is a difficult domain for computational as well as visualization purposes. We have therefore designed a set of procedures for modifying the representation of the c ..."
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Cited by 738 (57 self)
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The surface of the human cerebral cortex is a highly folded sheet with the majority of its surface area buried within folds. As such, it is a difficult domain for computational as well as visualization purposes. We have therefore designed a set of procedures for modifying the representation of the cortical surface to (i) inflate it so that activity buried inside sulci may be visualized, (ii) cut and flatten an entire hemisphere, and (iii) transform a hemisphere into a simple parameterizable surface such as a sphere for the purpose of establishing a surfacebased coordinate system.
A Survey of Shape Analysis Techniques
 Pattern Recognition
, 1998
"... This paper provides a review of shape analysis methods. Shape analysis methods play an important role in systems for object recognition, matching, registration, and analysis. Researchin shape analysis has been motivated, in part, by studies of human visual form perception systems. ..."
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Cited by 267 (2 self)
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This paper provides a review of shape analysis methods. Shape analysis methods play an important role in systems for object recognition, matching, registration, and analysis. Researchin shape analysis has been motivated, in part, by studies of human visual form perception systems.
A Framework For Efficient Minimum Distance Computations
, 1998
"... In this paper we present a framework for minimum distance computations that allows efficient solution of minimum distance queries on a variety of surface representations, including sculptured surfaces. The framework depends on geometric reasoning rather than numerical methods and can be implemented ..."
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Cited by 74 (11 self)
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In this paper we present a framework for minimum distance computations that allows efficient solution of minimum distance queries on a variety of surface representations, including sculptured surfaces. The framework depends on geometric reasoning rather than numerical methods and can be implemented straightforwardly. We demonstrate performance that compares favorably to other polygonal methods and is faster than reported results for other methods on sculptured surfaces. 1 Introduction We introduce a framework for minimum distance calculations that applies well to both polygonal and parametric model representations (Figure 1). The resulting methods scale well with problem size, have timecritical properties, and are interactive for large polygonal models and sculptured surfaces. In robotics, minimum distance queries have been used in path planning [2], path modification [25], and collision avoidance [15]. In computer graphics, minimum distance computations have played roles in physical...
Direct Haptic Rendering of Sculptured Models
 IN PROC. 1997 SYMPOSIUM ON INTERACTIVE 3D GRAPHICS
, 1997
"... A new tracing algorithm is described that supports haptic rendering of NURBS surfaces without the use of any intermediate representation. By using this tracing algorithm in conjunction with algorithms for surface proximity testing and surface transitions, a complete haptic rendering system for sculp ..."
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Cited by 59 (11 self)
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A new tracing algorithm is described that supports haptic rendering of NURBS surfaces without the use of any intermediate representation. By using this tracing algorithm in conjunction with algorithms for surface proximity testing and surface transitions, a complete haptic rendering system for sculptured models has been developed. The system links an advanced CAD modeling system with a Sarcos forcereflecting exoskeleton arm. A method for measuring the quality of the tracking component of the haptic rendering separately from the haptic device and force computation is also described.
Dynamic Motion Planning of Autonomous Vehicles
 IEEE Transactions on Robotics and Automation
, 1991
"... This paper presents a method for planning the motions of autonomous vehicles moving on general terrains. The method obtains the geometric path and vehicle speeds that minimize motion time consid ering vehicle dynamics, terrain topography, obstacles, and surface mobility. The terrain is represente ..."
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Cited by 53 (2 self)
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This paper presents a method for planning the motions of autonomous vehicles moving on general terrains. The method obtains the geometric path and vehicle speeds that minimize motion time consid ering vehicle dynamics, terrain topography, obstacles, and surface mobility. The terrain is represented by a smooth cubic B patch, and the geometric path consists of a B spline curve mapped to the surface. The time optimal motions are computed by first obtaining the best ohstacle free path from all paths represented by a uniform grid. This path is further optimized with a local optimization, using the optimal motion time along the path as the cost function and the control points of a B spline as the optimizing parameters. Examples are presented that demonstrate the method for a simple dynamic model of a vehicle moving on a mountainous terrain. I. INTRODUCTION T HE problem of motion planning of autonomous vehicles consistsof selecting the geometric path and vehicle speeds so as to avoi...
DAG  A Program that Draws Directed Graphs
, 1989
"... dag is a pic or POSTSCRIPT preprocessor that draws directed graphs. It works well on acyclic graphs and other graphs that can be drawn as hierarchies. Graph descriptions contain nodes, edges, and optional control statements. Here is a drawing of a graph from Forrester's book, World Dynamics (Wr ..."
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Cited by 53 (5 self)
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dag is a pic or POSTSCRIPT preprocessor that draws directed graphs. It works well on acyclic graphs and other graphs that can be drawn as hierarchies. Graph descriptions contain nodes, edges, and optional control statements. Here is a drawing of a graph from Forrester's book, World Dynamics (WrightAllen, Cambridge, MA, 1971). It took 2.1 CPU seconds on a VAX8650 to make this drawing. S8 9 S24 25 27 S1 2 10 S35 43 36 S30 31 33 42 T1 26 T24 3 16 17 18 11 14 13 12 32 T30 34 4 15 19 29 37 39 41 38 40 23 5 21 20 28 6 T35 22 7 T8 I. Introduction Directed graphs have many applications in computing, such as describing data structures, finite automata, data flow, procedure calls, and software configuration dependencies. A picture is a good way to represent a directed graph. It is seldom easy to understand much about a graph from a list of edges, but with a picture one can quickly find individual nodes, groups of related nodes, and trace paths in the graph. The main obstacle is that it can be...
CADBased Computer Vision: From CAD Models to Relational Graphs
 IEEE Transactions on Pattern Analysis and Machine Intelligence
, 1991
"... 3D object recognition is a difficult and yet an important problem in computer vision. A 3D object recognition system has two major componenb, object modeling (or representation) and matching stored representations to those derived from the sensed image. In this paper, we focus on the topic of model ..."
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Cited by 49 (2 self)
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3D object recognition is a difficult and yet an important problem in computer vision. A 3D object recognition system has two major componenb, object modeling (or representation) and matching stored representations to those derived from the sensed image. In this paper, we focus on the topic of modelbuildingfor 3D objecb. Most existing 3D object recognition systems construct models either manually, or by learning from multiple images of an object. Both these approaches have not been very satisfactory, particularly in designing object recognition systems which can handle a large number of objects. Recent interest in integrating mechanical CAD systems and vision systems has led to adaptation of preexisting CAD models of objects for recognition. If a solid model of an object to be recognized is already available in a manufacturing database, then we should be able to infer automatically a model appropriate for vision tasks Lom the manufacturing model. We have developed such a system which uaes 3D object descriptions created on a commercial CAD system and expressed in the industrystandard IGES form, and performs geometric inferencing to obtain a relational graph representation of the object which can be stored in a database of models for object recognition. Details of the IGES standard, the geometric inference engine, and some formal properties of 3D models are discussed. We believe that a system like ours is needed to efficiently create a large database (more than 100 objects) of 3D models to evaluate matching strategies. 1
Understanding Dynamic Scenes
, 2000
"... We propose a framework for the representation of visual knowledge in a robotic agent, with special attention to the understanding of dynamic scenes. According to our approach, understanding involves the generation of a high level, declarative description of the perceived world. Developing such a des ..."
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Cited by 44 (12 self)
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We propose a framework for the representation of visual knowledge in a robotic agent, with special attention to the understanding of dynamic scenes. According to our approach, understanding involves the generation of a high level, declarative description of the perceived world. Developing such a description requires both bottomup, data driven processes that associate symbolic knowledge representation structures with the data coming out of a vision system, and topdown processes in which high level, symbolic information is in its turn employed to drive and further refine the interpretation of a scene. On the one hand, the computer vision community approached this problem in terms of 2D/3D shape reconstruction and of estimation of motion parameters. On the other, the AI community developed rich and expressive systems for the description of processes, events, actions and, in general, of dynamic situations. Nevertheless, these two approaches evolved separately and concentrated on different kinds of problems. We propose an architecture that integrates these two traditions in a principled way. Our assumption is that a link is missing between the two classes of representations mentioned above. In order to fill this gap, we adopt the notion of conceptual space (CSGĂ¤rdenfors [58]), a representation where information is characterized in terms of a metric space. A CS acts as an intermediate representation between subconceptual (i.e., not yet conceptually categorized) information, and symbolically organized knowledge. The concepts of process and action have immediate characterizations in terms of structures in the conceptual space. The architecture is illustrated with reference to an experimental setup based on a vision system operating in a scenario with moving and interacting people.
An Efficient Algorithm for Finding the CSG Representation of a Simple Polygon
, 1989
"... Modeling twodimensional and threedimensional objects is an important theme in computer graphics. Two main types of models are used in both cases: boundary representations, which represent the surface of an object explicitly but represent its interior only implicitly, and constructive solid geometr ..."
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Cited by 37 (9 self)
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Modeling twodimensional and threedimensional objects is an important theme in computer graphics. Two main types of models are used in both cases: boundary representations, which represent the surface of an object explicitly but represent its interior only implicitly, and constructive solid geometry representations, which model a complex object, surface and interior together, as a boolean combination of simpler objects. Because neither representation is good for all applications, conversion between the two is often necessary. We consider the problem of converting boundary representations of polyhedral objects into constructive solid geometry (CSG) representations. The CSG representations for a polyhedron P are based on the halfspaces supporting the faces of P . For certain kinds of polyhedra this problem is equivalent to the corresponding problem for simple polygons in the plane. We give a new proof that the interior of each simple polygon can be represented by a monotone...
Deformable BSolids and Implicit Snakes for 3D Localization and Tracking of SPAMM MRIData
"... To date, MRISPAMM data from different image slices have been analyzed independently. In this paper, we propose an approach for 3D tag localization and tracking of SPAMM data by a novel deformable Bsolid. The solid is defined in terms of a 3D tensor product Bspline. The isoparametric curves of th ..."
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Cited by 36 (9 self)
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To date, MRISPAMM data from different image slices have been analyzed independently. In this paper, we propose an approach for 3D tag localization and tracking of SPAMM data by a novel deformable Bsolid. The solid is defined in terms of a 3D tensor product Bspline. The isoparametric curves of the Bspline solid have special importance. These are termed implicit snakes as they deform under image forces from tag lines in different image slices. The localization and tracking of tag lines is performed under constraints of continuity and smoothness of the Bsolid. To track motion from boundaries and restrict image forces to the myocardium, a volumetric model is employed as a pair of coupled endocardial and epicardial Bspline surfaces. To recover deformations of the Left Ventricle (LV) an energyminimization problem is posed where both tag and LV boundary data are used. The framework has been implemented on tag data from Short Axis (SA) cardiac images, as well as SA LV boundaries, and i...