Volume 23 Issue 01 - Publication Date: 1 January 2004
Visibility-Based Pursuit-Evasion in an Unknown Planar Environment
Shai Sachs, Steven M. LaValle Department of Computer Science, University of Illinois, Urbana, IL 61801, USA and Stjepan Rajko Department of Computer Science, Iowa State University, Ames, IA 50011, USA

We address an on-line version of the visibility-based pursuit-evasion problem.We take a minimalist approach in modeling the capabilities of a pursuer robot. A point pursuer moves in an unknown, simplyconnected, piecewise-smooth 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 wall-following 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.

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