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Anytime Guaranteed Search using Spanning Trees
, 2008
"... This technical report presents an anytime algorithm for solving the multirobot guaranteed search problem. Guaranteed search requires a team of robots to clear an environment of a potentially adversarial target. In other words, a team of searchers must generate a search strategy guaranteed to find a ..."
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This technical report presents an anytime algorithm for solving the multirobot guaranteed search problem. Guaranteed search requires a team of robots to clear an environment of a potentially adversarial target. In other words, a team of searchers must generate a search strategy guaranteed to find a target. This problem is known to be NPcomplete on arbitrary graphs but can be solved in lineartime on trees. Our proposed algorithm reduces an environment to a graph representation and then randomly generates a spanning tree of the graph. Guards are then placed on nodes in the graph to eliminate nontree edges, and a search strategy for the remaining tree is found using a lineartime algorithm from prior work. To reduce the number of guards, our algorithm takes advantage of the temporal characteristics of the search schedule to reuse guards no longer necessary at their previous locations. Many spanning trees are analyzed prior to search to determine the tree that yields the best search strategy. At any time, spanning tree generation can be stopped yielding the best strategy thus far. Our proposed algorithm is demonstrated on two complex graphs derived from physical environments, and several methods for generating candidate spanning trees are compared.
Searching the nodes of a graph: theory and algorithms
, 2009
"... One or more searchers must capture an invisible evader hiding in the nodes of a graph. We study this version of the graph search problem under additional restrictions, such as monotonicity and connectedness. We emphasize that we study node search, i.e., the capture of a nodelocated evader; this pro ..."
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One or more searchers must capture an invisible evader hiding in the nodes of a graph. We study this version of the graph search problem under additional restrictions, such as monotonicity and connectedness. We emphasize that we study node search, i.e., the capture of a nodelocated evader; this problem has so far received much less attention than edge search, i.e., the capture of an edgelocated evader. We show that in general graphs the problem of node search is easier than that of edge search, Namely, every edge clearing search is also node clearing, but the converse does not hold in general (however node search is NPcomplete, just like edge search). Then we concentrate on the internal monotone connected (IMC) node search of trees and show that it is essentially equivalent to IMC edge search; hence Barriere’s tree search algorithm [2], originally designed for edge search, can also be used for node search. We return to IMC node search on general graphs and present (several variants of) a new algorithm: GSST (Guaranteed Search by Spanning Tree). GSST clears a graph G by performing all its clearing moves along a spanning tree T of G. Because spanning trees can be generated and cleared very quickly, GSST can test a large number of spanning trees and find one which clears G with a small (though not necessarily minimal) number of searchers. We prove the existence of probabilistically complete variants of GSST (i.e., these variants are guaranteed to find a minimal IMC node clearing schedule if run for sufficiently long time). Our experiments also indicate that GSST can efficiently nodeclear large graphs given only a small running time. An implementation of GSST (running on Windows and Linux computers) is also provided and made publicly available. 1
GSST: anytime guaranteed search
, 2010
"... ... Trees (GSST), an anytime algorithm for multirobot search. The problem is as follows: clear the environment of any adversarial target using the fewest number of searchers. This problem is NPhard on arbitrary graphs but can be solved in lineartime on trees. Our algorithm generates spanning tree ..."
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Cited by 3 (1 self)
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... Trees (GSST), an anytime algorithm for multirobot search. The problem is as follows: clear the environment of any adversarial target using the fewest number of searchers. This problem is NPhard on arbitrary graphs but can be solved in lineartime on trees. Our algorithm generates spanning trees of a graphical representation of the environment to guide the search. At any time, spanning tree generation can be stopped yielding the best strategy so far. The resulting strategy can be modified online if additional information becomes available. Though GSST does not have performance guarantees after its first iteration, we prove that several variations will find an optimal solution given sufficient runtime. We test GSST in simulation and on a humanrobot search team using a distributed implementation. GSST quickly generates clearing schedules with as few as 50 % of the searchers used by competing algorithms.
J.S.: Adaptive learning approach of fuzzy logic controller with evolution for pursuit–evasion games
 ICCCI 2010, Part I. LNCS (LNAI
, 2010
"... Abstract. This paper studies a simplified pursuitevasion problem. We assume that the evader moves with constant speed along a trajectory that is welldefined and known a priori. The objective of steering control of the pursuer modeled as a nonholonomic unicycletype mobile robot is to intercept the ..."
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Abstract. This paper studies a simplified pursuitevasion problem. We assume that the evader moves with constant speed along a trajectory that is welldefined and known a priori. The objective of steering control of the pursuer modeled as a nonholonomic unicycletype mobile robot is to intercept the moving evader. An adaptive learning approach of fuzzy logic controller is developed as an inverse kinematics solver of unicycle to enable a mobile robot to use the evader trajectory to adapt its control actions to pursuitevasion game. In this proposed approach, GA evolves the parameter values of the fuzzy logic control system aiming to approximate the inverse kinematics of pursuer so as to generate a trajectory capturing the evader. Simulation results of pursuitevasion game illustrate the performance of the proposed approach.
Continuous Graph Partitioning for Camera Network Surveillance
"... In this work we design surveillance trajectories for a network of autonomous cameras to detect intruders in an environment. Intruders, which appear at arbitrary times and locations, are classified as static or dynamic. While static intruders remain stationary, dynamic intruders are aware of the came ..."
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In this work we design surveillance trajectories for a network of autonomous cameras to detect intruders in an environment. Intruders, which appear at arbitrary times and locations, are classified as static or dynamic. While static intruders remain stationary, dynamic intruders are aware of the cameras configuration and move to avoid detection, if possible. As performance criteria we consider the worstcase detection time of static and dynamic intruders. We model the environment and the camera network by means of a robotic roadmap. We show that optimal cameras trajectories against static intruders are obtained by solving a continuous graph partitioning problem. We design centralized and distributed algorithms to solve this continuous graph partitioning problem. Our centralized solution relies on tools from convex optimization. For the distributed case, we consider three distinct cameras communication models and propose a corresponding algorithm for each of the models. Regarding dynamic intruders, we identify necessary and sufficient conditions on the cameras locations to detect dynamic intruders in finite time. Additionally, we construct constantfactor optimal trajectories for the case of ring and tree roadmaps.
Blind Submission #10
, 2010
"... We are looking forward to attending your workshop to discuss our recent work on probabilistic pursuit of adversarial evaders. Attached we have included some of our work which is currently under review at RSS. Our presentation at the workshop would borrow heavily from the RSS paper, but would also in ..."
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We are looking forward to attending your workshop to discuss our recent work on probabilistic pursuit of adversarial evaders. Attached we have included some of our work which is currently under review at RSS. Our presentation at the workshop would borrow heavily from the RSS paper, but would also include some additional work on dynamically responding to evaders of varying adversarialness. Please let us know if you have any questions or concerns. Sincerely,
Connected searching of weighted trees
"... In this paper we consider the problem of connected edge searching of weighted trees. Barrière et al. claim in [Capture of an intruder by mobile agents, SPAA’02 (2002) 200209] that there exists a polynomialtime algorithm for finding an optimal search strategy, that is, a strategy that minimizes th ..."
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In this paper we consider the problem of connected edge searching of weighted trees. Barrière et al. claim in [Capture of an intruder by mobile agents, SPAA’02 (2002) 200209] that there exists a polynomialtime algorithm for finding an optimal search strategy, that is, a strategy that minimizes the number of used searchers. However, due to some flaws in their algorithm, the problem turns out to be open. It is proven in this paper that the considered problem is strongly NPcomplete even for nodeweighted trees (the weight of each edge is 1) with one vertex of degree greater than 2. It is also shown that there exists a polynomialtime algorithm for finding an optimal connected search strategy for a given bounded degree tree with arbitrary weights on the edges and on the vertices. This is an FPT algorithm with respect to the maximum degree of a tree.
Synthesizing Strategies for Epistemic Goals by Epistemic Model Checking: an application to Pursuit Evasion Games ∗
"... The paper identifies a special case in which the complex problem of synthesis from specifications in temporalepistemic logic can be reduced to the simpler problem of model checking such specifications. An application is given of strategy synthesis in pursuitevasion games, where one or more pursuer ..."
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The paper identifies a special case in which the complex problem of synthesis from specifications in temporalepistemic logic can be reduced to the simpler problem of model checking such specifications. An application is given of strategy synthesis in pursuitevasion games, where one or more pursuers with incomplete information aim to discover the existence of an evader. Experimental results are provided to evaluate the feasibility of the approach.
Search and Pursuit with Unmanned Aerial Vehicles in Road Networks
, 2013
"... Across many rescue, surveillance, and scientific applications, there exists a broad need to perform widearea reconnaissance and terrain surveys, for which unmanned aerial vehicles (UAVs) are increasingly popular. This thesis considers the task of using one or more UAVs to locate an object of inte ..."
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Across many rescue, surveillance, and scientific applications, there exists a broad need to perform widearea reconnaissance and terrain surveys, for which unmanned aerial vehicles (UAVs) are increasingly popular. This thesis considers the task of using one or more UAVs to locate an object of interest, provide continuous viewing, and rapidly reacquire tracking should it be lost for any reason. For both the common class of small fieldlaunched UAVs considered as well as larger UAVs, this is a difficult task due to a small available sensor field of view, uncertain estimates of UAV pose, and limited maneuverability relative to the scale of the environment, requiring constant processing of observations and recomputation of flight paths or sensor aiming to best find the object or keep it in view. Existing strategies for accomplishing this provide poor estimates of the object’s location and rely on grossly heuristic or computationally intensive trajectory genera
forCameraNetworksSurveillance
"... In this note we discuss a novel graph partitioning problem, namely continuous graph partitioning, and we discuss its application to the design of surveillance trajectories for camera networks. In continuous graph partitioning, each edge is partitioned in a continuous fashion between its endpoint ver ..."
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In this note we discuss a novel graph partitioning problem, namely continuous graph partitioning, and we discuss its application to the design of surveillance trajectories for camera networks. In continuous graph partitioning, each edge is partitioned in a continuous fashion between its endpoint vertices, and the objective is to minimize the largest load among the vertices. We show that the continuous graph partitioning problem is convex and nondifferentiable, and we characterize a solution amenable to distributed computation. The continuous graph partitioning problem naturally arises in the context of camera networks, where intruders appear at arbitrary locations and times, and the objective is to design camera trajectories for quickest detection of intruders. Finally, we propose a surveillance strategy for networks of PTZ cameras and we characterize its performance. Key words: Graph partitioning, constrained optimization, camera network, distributed control. 1