Construction sites are rugged, dynamic, and complex, involving a large number of objects that continuously change their locations and occupied spaces. Being able to accurately locate and track site objects site is critical to project management and control to meet the increasing demands for efficiency and safety in modern construction projects. Automated locating technologies such as Radio Frequency Identification (RFID) have proven to be beneficial in tracking some construction site objects. The biggest challenge in applying the RFID technology is that the received signal strength (RSS) varies over time and location, and there is no direct relationship between signal strength and detection range, leading to low positional accuracies in the estimated tag locations. This paper presents an algorithm termed BConTri that combines a “boundary condition method” and the trilateration concept to estimate tag location in three-dimensional (3D) real world coordinates from four or more RFID readers equipped with GPS. This study also developed a prototype RFID locating system that implemented the newly created BConTri algorithm. A comprehensive assessment of the positional accuracy was applied to field experiment results and a high accuracy of the algorithm was observed. A measure of the spatial dilution of reader distribution was formulated and a linear relationship between this measure and the locating accuracy was observed, forming the base for using this measure as a reliable indicator for the resulting locating accuracy. This accuracy indicator helps in estimating the accuracy and quality control of RFID-based locating and tracking systems in construction. 
A boundary condition based algorithm for locating construction site objects using RFID and GPS