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.