Using reference RFID tags for calibrating the estimated locations of construction materials

Effective automated tracking and locating of the thousands of materials on construction sites improve materials management and project performance. Utilizing location sensing technologies such as RFID, GPS, Ultra-wideband, infrared, and others help to achieve this objective; however, they generally provide imperfect data which results in lack of accuracy, precision and robustness. One possibility of improving the precision, accuracy, and robustness of such systems is the use of reference tags. In this paper active RFID tags are employed as reference points at known and fixed locations on a construction site and are used to calibrate the location estimation of other materials on the site. Materials on the site are uniquely attached with RFID tags and are subject to tracking. The basic principle of the calibration technique using reference points is to adjust the estimated location of neighboring tags by adding a unique offset vector to each individual tag location-estimation. In a two level approach, first the locations of all tags are estimated using a proximity method. Then a unique offset vector is calculated and added to each individual tag location to calibrate the estimated location in level 1. The offset vector is a weighted average of the shift-vectors between the observed and the true location of the reference tags. The weights are based on the relative distance between the observed location of the target tag and the reference tags. The experimental results show that calibrating the location estimates using reference tags can successfully deal with the challenges of a very noisy and dynamic environment and imperfect construction data and improve the precision of the estimated locations.