Proximity Graphs for Crowd Movement Sensors

Sensors are now common, they span over different applications, different purposes and some over large geospatial areas. Most data produced by these sensors needs to be linked to the physical location of the sensor itself. By using the location of a sensor we can construct (mathematically) proximity graphs that have the sensors as nodes. These graphs have a wide variety of applications including visualization, packet routing, and spatial data analysis. We consider a sensor network that measures detections of WiFi packets transmitted by devices, such as smartphones. One important feature of sensors is given by the range in which they can gather data. Algorithms that build proximity graphs do not take this radius into account. We present an approach to building proximity graph that takes sensor position and radius as input. Our goal is to construct a graph that contains edges between pairs of sensors that are correlated to crowd movements, reflecting paths that individuals are likely to take. Because we are considering crowd movement, it gives us the unique opportunity to construct graphs that show the connections between sensors using consecutive detections of the same device. We show that our approach is better than ones that are based on the positioning of sensors only.