TY - JOUR
T1 - The Impact of Height on Indoor Positioning with Magnetic Fields
AU - Hanley, David
AU - De Oliveira, Augusto S.Dantas
AU - Zhang, Xiangyuan
AU - Kim, Dae Hyun
AU - Wei, Yusheng
AU - Bretl, Timothy
N1 - Funding Information:
Manuscript received November 16, 2020; revised January 5, 2021; accepted January 22, 2021. Date of publication February 12, 2021; date of current version March 4, 2021. This work was supported by the National Science Foundation under Grant 14-46765, Grant 14-27111, and Grant 15-44999. The Associate Editor coordinating the review process was Dr. Jesús Ureña. (Corresponding author: David Hanley.) David Hanley, Xiangyuan Zhang, and Yusheng Wei are with the Department of Electrical and Computer Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801 USA (e-mail: hanley6@illinois.edu; xz7@illinois.edu; ywei26@illinois.edu).
Funding Information:
The authors would like to thank Scott D. Zelman and Siddharth Chadha for help constructing portions of our experimental rig. This work made use of the Illinois Campus Cluster, a computing resource that is operated by the Illinois Campus Cluster Program (ICCP) in conjunction with the National Center for Supercomputing Applications (NCSA) and that is supported by funds from the University of Illinois.
Publisher Copyright:
© 1963-2012 IEEE.
PY - 2021
Y1 - 2021
N2 - Steel studs, heating, ventilation, and air conditioning (HVAC) systems, rebar, and many other building components produce spatially varying magnetic fields. Magnetometers can measure these fields and can be used in combination with inertial sensors for indoor positioning of robots and handheld devices, such as smartphones. Current methods of localization and mapping with magnetometers are often based on the simplifying assumption that magnetic fields do not vary with height. In this article, through the analysis of a large data set collected across three buildings on the University of Illinois campus, we quantify the extent to which this 'planar assumption' is likely to be violated and examine the consequences for indoor positioning. First, we show that out-of-plane variations in the magnetic field were significant at over half the locations where magnetometer measurements were taken. Second, we show that absolute trajectory error in positioning was low when both localization and mapping were based on magnetometer measurements taken at the same height, but that error increased significantly with even small differences between these heights. Third, we show that the choice of height at which to take measurements-if this height was kept the same for both localization and mapping-had no significant impact on absolute trajectory error when averaged across a given set of trajectories although some trajectories existed for which different measurement heights led to significantly different errors. Fourth, we show that absolute trajectory error decreased when magnetometer measurements were aggregated across a small range of heights to produce a single, planar map and when measurements at the median height were used for localization.
AB - Steel studs, heating, ventilation, and air conditioning (HVAC) systems, rebar, and many other building components produce spatially varying magnetic fields. Magnetometers can measure these fields and can be used in combination with inertial sensors for indoor positioning of robots and handheld devices, such as smartphones. Current methods of localization and mapping with magnetometers are often based on the simplifying assumption that magnetic fields do not vary with height. In this article, through the analysis of a large data set collected across three buildings on the University of Illinois campus, we quantify the extent to which this 'planar assumption' is likely to be violated and examine the consequences for indoor positioning. First, we show that out-of-plane variations in the magnetic field were significant at over half the locations where magnetometer measurements were taken. Second, we show that absolute trajectory error in positioning was low when both localization and mapping were based on magnetometer measurements taken at the same height, but that error increased significantly with even small differences between these heights. Third, we show that the choice of height at which to take measurements-if this height was kept the same for both localization and mapping-had no significant impact on absolute trajectory error when averaged across a given set of trajectories although some trajectories existed for which different measurement heights led to significantly different errors. Fourth, we show that absolute trajectory error decreased when magnetometer measurements were aggregated across a small range of heights to produce a single, planar map and when measurements at the median height were used for localization.
KW - Gaussian process
KW - indoor localization
KW - magnetic field mapping
KW - magnetic localization
KW - particle filter
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U2 - 10.1109/TIM.2021.3059317
DO - 10.1109/TIM.2021.3059317
M3 - Article
AN - SCOPUS:85100869532
SN - 0018-9456
VL - 70
JO - IEEE Transactions on Instrumentation and Measurement
JF - IEEE Transactions on Instrumentation and Measurement
M1 - 9354181
ER -