Abstract
While the undisturbed Earth’s magnetic field represents a fundamental information source for orientation purposes, magnetic distortions have been mostly considered as a source of error. However, when distortions are temporally stable and spatially distinctive, they could provide a unique magnetic landscape that can be used in different applications, from indoor localization to sensor fusion algorithms for attitude estimation. The main purpose of this work, therefore, is to present a method to characterize the 3D magnetic vector in every point of the measurement volume. The possibility of describing the 3D magnetic field map through Thin Plate Splines (TPS) interpolation is investigated and demonstrated. An algorithm for the simultaneous estimation of the parameters related to magnetometer calibration and those describing the magnetic map, is proposed and tested on both simulated and real data. Results demonstrate that an accurate description of the local magnetic field using TPS interpolation is possible. The proposed procedure leads to errors in the estimation of the local magnetic direction with a standard deviation lower than 1 degree. Magnetometer calibration and magnetic field mapping could be integrated into different algorithms, for example to improve attitude estimation in highly distorted environments or as an aid to indoor localization.
Highlights
IntroductionEvidence suggests that the animals use Earth’s magnetic field as well [1,2]
The Earth’s magnetic field has been used by the humans for centuries as a navigation tool.Evidence suggests that the animals use Earth’s magnetic field as well [1,2]
It is well known that the Earth’s magnetic field is not a predefined and time-constant vector [4]. It depends on the latitude and longitude coordinates and suffers from different types of fluctuations due to the diurnal cycle, movement of magnetic poles, and more randomly, to geomagnetic storms caused by solar flares [5], but for all practical purposes, especially for the use of magnetic data in sensor fusion algorithms to estimate the local orientation of a Magnetic and Inertial Measurement Unit (MIMU), these fluctuations are negligible when compared to the typical point to point variation of magnetic field inside a building [4,6,7]
Summary
Evidence suggests that the animals use Earth’s magnetic field as well [1,2] Some animals, such as spiny lobsters, are able to detect the direction of Earth’s magnetic field, they can even sense their true position relative to their destination [3]. Their ability seems to suggest that the knowledge of magnetic information could lead to the determination of the position. Its intensity and direction strongly depend on the proximity of metallic objects with high relative permeability, such as iron reinforcements in buildings, permanent magnets, motors and electronic devices
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