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76
SelfConfiguring Localization Systems: Design and Experimental Evaluation
 ACM TRANSACTIONS ON EMBEDDED COMPUTING SYSTEMS
, 2003
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Sweeping simple polygons with a chain of guards
 In Proceedings of the 11th ACMSIAM Symposium on Discrete Algorithms (SODA
, 2000
"... Abstract We consider the problem of locating a continuouslymoving target using a group of guardsmoving inside a simple polygon. Our guards always form a simple polygonal chain within the polygon such that consecutive guards along the chain are mutually visible. We developalgorithms that sweep such ..."
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Cited by 36 (2 self)
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Abstract We consider the problem of locating a continuouslymoving target using a group of guardsmoving inside a simple polygon. Our guards always form a simple polygonal chain within the polygon such that consecutive guards along the chain are mutually visible. We developalgorithms that sweep such a chain of guards through a polygon to locate the target. Our two main results are the following: 1. an algorithm to compute the minimum number r * of guards needed to sweep an nvertexpolygon that runs in O(n3) time and uses O(n2) working space, and 2. a faster algorithm, using O(n log n) time and O(n) space, to compute an integer r suchthat max( r 16, 2) < = r * < = r and P can be swept with a chain of r guards. We develop two other techniques to approximate r*. Using O(n2) time and space, we show howto sweep the polygon using at most r * + 2 guards. We also show that any polygon can be sweptby a number of guards equal to two more than the link radius of the polygon. As a key component of our exact algorithm, we introduce the notion of the link diagramof a polygon, which encodes the link distance between all pairs of points on the boundary of the polygon. We prove that the link diagram has size \Theta (n3) and can be constructed in \Theta (n3)time. We also show link diagram provides a data structure for optimal twopoint linkdistance queries, matching an earlier result of Arkin et al.As a key component of our O(n log n)time approximation algorithm, we introduce the notionof the "link width " of a polygon, which may have independent interest, as it captures important
Visibilitybased pursuitevasion in an unknown planar environment
 International Journal of Robotics Research
, 2004
"... We address an online version of the visibilitybased pursuitevasion problem. We take a minimalist approach in modeling the capabilities of a pursuer robot. A point pursuer moves in an unknown, simplyconnected, piecewisesmooth planar environment, and is given the task of locating any unpredictable ..."
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Cited by 35 (8 self)
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We address an online version of the visibilitybased pursuitevasion problem. We take a minimalist approach in modeling the capabilities of a pursuer robot. A point pursuer moves in an unknown, simplyconnected, piecewisesmooth planar environment, and is given the task of locating any unpredictable, moving evaders that have unbounded speed. The evaders are assumed to be points that move continuously. To solve the problem, the pursuer must for each target have an unobstructed view of it at some time during execution. The pursuer is equipped with a range sensor that measures the direction of depth discontinuities, but cannot provide precise depth measurements. All pursuer control is specified either in terms of this sensor or wallfollowing movements. The pursuer does not have localization capability or perfect control. We present a complete algorithm that enables the limited pursuer to clear the same environments that a pursuer with a complete map, perfect localization, and perfect control can clear (under certain general position assumptions). Theoretical guarantees that the evaders will be found are provided. The resulting algorithm to compute this strategy has been implemented in simulation. Results are shown for several examples. The approach is efficient and simple enough to be useful towards the development of real robot systems that perform visual searching. 1
Planning Robot Motion Strategies for Efficient Model Construction
"... This paper considers the computation of motion strategies to efficiently build polygonal layouts of indoor environments using a mobile robot equipped with a range sensor. This problem requires repeatedly answering the following question while the model is being built: Where should the robot go to pe ..."
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Cited by 33 (3 self)
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This paper considers the computation of motion strategies to efficiently build polygonal layouts of indoor environments using a mobile robot equipped with a range sensor. This problem requires repeatedly answering the following question while the model is being built: Where should the robot go to perform the next sensing operation? A nextbestview planner is proposed which selects the robot's next position that maximizes the expected amount of new space that will be visible to the sensor. The planner also takes into account matching requirements for reliable selflocalization of the robot, as well as physical limitations of the sensor (range, incidence). The paper argues that polygonal layouts are a convenient intermediate model to perform other visual tasks. 1. Introduction Automatic model construction is a core problem in mobile robotics [1, 2, 3]. After being introduced into an unknown environment, a robot, or a team of robots, must perform sensing operations at multiple locations...
Gap navigation trees: Minimal representation for visibilitybased tasks
 In Proc. Workshop on the Algorithmic Foundations of Robotics
, 2004
"... Abstract. In this paper we present our advances in a data structure, the Gap Navigation Tree (GNT), useful for solving different visibilitybased robotic tasks in unknown planar environments. We present its use for optimal robot navigation in simplyconnected environments, locally optimal navigation ..."
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Cited by 22 (10 self)
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Abstract. In this paper we present our advances in a data structure, the Gap Navigation Tree (GNT), useful for solving different visibilitybased robotic tasks in unknown planar environments. We present its use for optimal robot navigation in simplyconnected environments, locally optimal navigation in multiplyconnected environments, pursuitevasion, and robot localization. The guiding philosophy of this work is to avoid traditional problems such as complete map building and exact localization by constructing a minimal representation based entirely on critical events in online sensor measurements made by the robot. The data structure is introduced from an information space perspective, in which the information used among the different visibilitybased tasks is essentially the same, and it is up to the robot strategy to use it accordingly for the completion of the particular task. This is done through a simple sensor abstraction that reports the discontinuities in depth information of the environment from the robot’s perspective (gaps), and without any kind of geometric measurements. The GNT framework was successfully implemented on a real robot platform. 1
Scalable, Ad Hoc Deployable RFbased Localization
 IN PROCEEDINGS OF THE GRACE HOPPER CONFERENCE ON CELEBRATION OF WOMEN IN COMPUTING
, 2002
"... Spatial localization or the ability to locate nodes is an important building block for next generation pervasive computing systems, but a formidable challenge, particularly, for very small hardware and energy constrained devices, for noisy, unpredictable environments and for very large ad hoc deploy ..."
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Cited by 22 (0 self)
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Spatial localization or the ability to locate nodes is an important building block for next generation pervasive computing systems, but a formidable challenge, particularly, for very small hardware and energy constrained devices, for noisy, unpredictable environments and for very large ad hoc deployed and networked systems. In this paper, we describe, validate and evaluate in real environments a very simple self localization methodology for RFbased devices based only on RFconnectivity constraints to a set of beacons (known nodes), applicable outdoors. Beacon placement has a significant impact on the localization quality in these systems. To selfconfigure and adapt the localization in noisy environments with unpredictable radio propagation vagaries, we introduce the novel concept of adaptive beacon placement. We propose several novel and density adaptive algorithms for beacon placement and demonstrate their effectiveness through evaluations. We also outline an approach in which beacons leverage a software controllable variable transmit power capability to further improve localization granularity. These combined features allow a localization system that is scalable and ad hoc deployable, longlived and robust to noisy environments. The unique aspect of our localization approach is our emphasis on adaptive selfconfiguration.
An Algorithm for Searching a Polygonal Region with a Flashlight
 International Journal of Computational Geometry and Applications
, 2000
"... We present an algorithm for a single pursuer with one ashlight that searches for an unpredictable, moving target with unbounded speed in a polygonal environment. The algorithm decides whether a simple polygon with n edges and m concave regions (m is typically much less than n, and always bounded ..."
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Cited by 22 (4 self)
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We present an algorithm for a single pursuer with one ashlight that searches for an unpredictable, moving target with unbounded speed in a polygonal environment. The algorithm decides whether a simple polygon with n edges and m concave regions (m is typically much less than n, and always bounded by n) can be cleared by the pursuer, and if so, constructs a search schedule in time O(m 2 + m log n + n). The key ideas in this algorithm include a representation called the \visibility obstruction diagram" and its \skeleton," which is a combinatorial decomposition based on a number of critical visibility events. An implementation is presented along with a computed example. 1 Introduction Consider the following scenario: in a dark polygonal region there are two moving points. The rst one, called the pursuer, has the task to nd the second one, called the evader. The evader can move arbitrarily fast, and his movements are unpredictable by the pursuer. The pursuer is equipped with a...
Efficient MultiRobot Search for a Moving Target
"... This paper examines the problem of locating a mobile, nonadversarial target in an indoor environment using multiple robotic searchers. One way to formulate this problem is to assume a known environment and choose searcher paths most likely to intersect with the path taken by the target. We refer to ..."
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Cited by 21 (12 self)
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This paper examines the problem of locating a mobile, nonadversarial target in an indoor environment using multiple robotic searchers. One way to formulate this problem is to assume a known environment and choose searcher paths most likely to intersect with the path taken by the target. We refer to this as the Multirobot Efficient Search Path Planning (MESPP) problem. Such path planning problems are NPhard, and optimal solutions typically scale exponentially in the number of searchers. We present an approximation algorithm that utilizes finitehorizon planning and implicit coordination to achieve linear scalability in the number of searchers. We prove that solving the MESPP problem requires maximizing a nondecreasing, submodular objective function, which leads to theoretical bounds on the performance of our approximation algorithm. We extend our analysis by considering the scenario where searchers are given noisy nonlineofsight ranging measurements to the target. For this scenario, we derive and integrate online Bayesian measurement updating into our framework. We demonstrate the performance of our framework in two largescale simulated environments, and we further validate our results using data from a novel ultrawideband ranging sensor. Finally, we provide an analysis that demonstrates the relationship between MESPP and the intuitive average capture time metric. Results show that our proposed linearly scalable approximation algorithm generates searcher paths competitive with those generated by exponential algorithms. 1
A pursuitevasion BUG algorithm
 In Proc. IEEE Int’l Conf. on Robotics and Automation
, 1954
"... We consider the problem of searching for an unpredictable moving target, using a robot that lacks a map of the environment, lacks the ability to construct a map, and has imperfect navigation ability. We present a complete algorithm, which yields a motion strategy for the robot that guarantees the el ..."
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Cited by 20 (13 self)
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We consider the problem of searching for an unpredictable moving target, using a robot that lacks a map of the environment, lacks the ability to construct a map, and has imperfect navigation ability. We present a complete algorithm, which yields a motion strategy for the robot that guarantees the elusive target will be detected, if such a strategy exists. It is assumed that the robot has an omnidirectional sensing device that is used to detect moving targets and also discontinuities in depth data in a 2D environment. We also show that the robot has the same problemsolving power as a robot that has a complete map and perfect navigation abilities. The algorithm has been implemented in simulation, and some examples are shown. 1
Motion Planning with Visibility Constraints: Building Autonomous Observers
 PROCEEDINGS OF THE EIGHTH INTERNATIONAL SYMPOSIUM OF ROBOTICS RESEARCH
, 1998
"... Autonomous Observers are mobile robots that cooperatively perform vision tasks. Their design raises new issues in motion planning, where visibility constraints and motion obstructions must be simultaneously taken into account. This paper presents the concept of an Autonomous Observer and its applica ..."
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Cited by 19 (5 self)
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Autonomous Observers are mobile robots that cooperatively perform vision tasks. Their design raises new issues in motion planning, where visibility constraints and motion obstructions must be simultaneously taken into account. This paper presents the concept of an Autonomous Observer and its applications. It discusses three problems in motion planning with visibility constraints: model building, target finding, and target tracking.