Camera Placement For Global Vision

Abstract

Stationary visual cameras, or what is termed vision, can be used to provide the information necessary for the control of multiple free-ranging auto- matic guided vehicles in order to expand the range of applications for which they are a high-performance and cost-effective transport alternative. The camera placement problem of global vision refers to determining, for a given facility layout, a minimal number of cameras necessary to implement global vision-based control and their positions in the facility. In this paper, the camera placement prob- lem of global vision is formulated and analyzed for its computational complexity and is shown to be NP-hard, and a convex hull-based greedy algorithm is described for its approximate solution. I. INTRODUCTION Stationary visual cameras, or what is termed vision, can be used to provide the information necessary for the control of free-ranging automatic guided vehicle (AGV) systems. Global vision provides a means to robustly control AGV systems composed of large numbers of low-cost free- ranging vehicles that are able to operate in unrestricted indoor environments. The sensory information used for the control of the free-ranging AGV system is provided by global vision and low-cost range sensors on board each vehicle. A system with these capabilities will expand the range of applications for which they are a high-performance and cost-effective material transport alternative. The development of a means to achieve these capabilities was the principal motivation for proposing global vision-based free-ranging AGV control (3). Global vision refers to the use of cameras placed at fixed locations in a workspace to extend the local sensing available on board each vehicle in a free-ranging AGV system. Information from the cameras is used to (a) monitor the workspace to detect and track potential obstacles both in the immediate vicinity of each AGV and over its intended path; (b) track each AGV along its intended path to bound errors in the vehicle's dead-reckoning sensors; (c) monitor the load aboard each AGV to detect positioning errors; and, as a side benefit, (d) provide video images of the entire workspace so that a human operator can monitor the status of operations throughout the facility. Figure 1 shows the major components of global vision- based AGV control. The cameras for global vision are placed at fixed locations throughout a facility. Their unprocessed video signals are sent both to TV screens, where they could be used to monitor the status of on-going operations, and to a central processing site, where global vision-based vehicle control takes place. The status of the AGV system is available as input to high-level transport control functions (e.g., vehicle dispatching). Although only two cameras are shown in the figure, more cameras would typically be used in practice. Each vehicle has a communications link with the central pro- cessing site to receive control commands and to transmit the results of its on-board sensing operations. A. Limitations of Current AGV Systems