Positioning Systems: Global Versus Local
Current technology developments are addressed toward the wide class of bio-inspired achievements. Herds, flocks, shoals, all of them solve their relative positioning problems by vision schemes, which are presently requiring high technology and large stora
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Abstract Current technology developments are addressed toward the wide class of bio-inspired achievements. Herds, flocks, shoals, all of them solve their relative positioning problems by vision schemes, which are presently requiring high technology and large storage masses. At a more affordable level, global positioning systems (GPS) are well established but they cannot be used indoor or within an urban environment. The number of visible satellites fluctuates from time to time and this is affecting the accuracy of any GPS receiver. Local positioning systems (LPS) are a valuable alternative. LPS is made of positioning sensors and at least four transponders which periodically transmit reference signals. The realization of a non-proprietary positioning sensor is sketched and discussed with focus on the levels of accuracy which can be achieved.
1 Introduction Structural health monitoring (SHM), which diagnoses the health situation of structures according to their dynamic or static response, aims to improve the safety of human life and the performance of the societal arrangement. The data-base obtained from a SHM system can also be used to validate the design, study the dynamic characteristics of structures of new conception, and monitor the health situation of existing buildings. Within SHM, a positioning system plays two different roles. First, the relative positioning, i.e., the displacement is a main physical variable from which the stress and the strain can be easily obtained. In this context, a global positioning system (GPS) sensor provides an absolute displacement measure at any time along any day
F. Casciati () L.J. Wu Department of Structural Mechanics, University of Pavia, Pavia, Italy e-mail: [email protected]; [email protected] H. Irschik et al. (eds.), Advanced Dynamics and Model-Based Control of Structures and Machines, DOI 10.1007/978-3-7091-0797-3 6, © Springer-Verlag/Wien 2012
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provided that an open vision of the sky is available. The second role results from the fact that many new kinds of sensor are introduced in order to monitor largescale structures [1]. Mobile sensors are a viable solution in order to achieve a high density monitoring system by a limited number of sensors [2]. The position of each sensor however is a required information, easily achievable, for instance, by GPS. High performance GPS sensors, i.e., geodesic GPS sensors, can measure the absolute displacement of the object point and achieve an accuracy of the order of centimeters [3, 4]. A GPS receiver is a non-contact sensor, which therefore can be easily installed. Signals from satellites cover a large range, but GPS sensors can only be effective in open sky. Furthermore, the geometry distribution of visible satellites fluctuates from time to time [5]. All these remarks affect the positioning accuracy from time to time and place to place. A valuable alternative would be the adoption of local positioning systems (LPS). One measures the distance from a transponder to the sensor by working on
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