pose tracking of magnetic objects - it.uu.se filepose tracking of magnetic objects niklas wahlstrom...

Pose tracking of magnetic objects

Niklas Wahlstrom

Department of Information Technology, Uppsala University, Sweden

February 2, 2018

[email protected] VASCO workshop

mailto:[email protected]

Magnetometer measurement models

1. Common use: Magnetometer provides orientationinformation.

Assume that the magnetometer (almost) only measures thelocal (earth) magnetic field.

2. My use: Magnetometer(s) to provide position andorientation information.

I Magnetic mapping: Build a map of the (indoor) magneticfield.

I Magnetic tracking: Measure the position and orientation of aknown magnetic source.

1 / 17 [email protected] VASCO workshop


Magnetic mapping

Build a map of the indoor magnetic field. This map can be usedfor localization.

We have used Bayesian models (Gaussian processes) to model suchfields with good results



Magnetometer measurement models

1. Common use: Magnetometer provides orientationinformation.

Assume that the magnetometer (almost) only measures thelocal (earth) magnetic field.

2. My use: Magnetometer(s) to provide position andorientation information.

I Magnetic mapping: Build a map of the (indoor) magneticfield.

I Magnetic tracking: Measure the position and orientation of aknown magnetic source.



Sensor setup

We use a sensor network with four three-axis magnetometers todetermine the position and orientation of a magnet.



Magnetic tracking

Advantages

I Cheap sensors

I Small sensors

I Low energy consumption

I No weather dependency

I Passive unit, requires nobatteries



Mathematical model - dipole field

The magnetic field can be described with a dipole field.

J(r′)

mr

B(r)

B(r) =µ0

4π‖r‖5(3r · rT − ‖r‖2I3

)︸︷︷︸

=C(r)

m

m ,1

2

∫r′ × J(r′)d3r′



Sensor model - single dipole

The measurements can be described with a state-space model

xk+1 = Fkxk +Gkwk, wk ∼ N (0, Q),

yk,j = hj(xk) + ek, ek ∼ N (0, R)

Point target sensor model (one dipole)

hj(xk) = C(rk − θj)mk, xk = [rTk vTk mT

k ωTk ]

T

C(r) =µ0

4π‖r‖5 (3rrT − ‖r‖2I3),

Measurement from a sensor network ofmagnetometers positioned at {θj}Jj=1.

Degrees of freedom

I 3D position

I 2D orientation



Experiment 1

0.2

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y-coordinate [m]

0

Trajectory

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x-coordinate [m]

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z-co

ordi

nate

[m]

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Trajectory

-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2y-coordinate [m]

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z-co

ordi

nate

[m]

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Theaccuracy is



Experiment 2 - setup



Experiment 2 - results - position

20 25 30 35 40 45 50

−0.2

−0.1

0

0.1

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Time [s]

Posi

tion

[m]

Black: Ground truth position. Color: Estimated position



Experiment - results - orientation

20 25 30 35 40 45 50−200

−100

0

100

Time [s]

Ori

enta

tion

[deg

ree]

Black: Ground truth orientation. Color: Estimated orientation



Application 1: 3D painting book



Application 2: Digital water colors



Application 3: Digital table hockey



Application 4: Digital pathology



Stylaero AB

I In February 2017 acompany was startedaround this technology

I In total seven people areinvolved in the companyon part-time.

I Collaborations with bothgaming companies andindustrial partners.



Thank you!



pose tracking of magnetic objects - it.uu.se filepose tracking of magnetic objects niklas wahlstrom...

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