The GETA Sandals: A Footprint Location Tracking System
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Transcript of The GETA Sandals: A Footprint Location Tracking System
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The GETA Sandals: A Footprint Location Tracking System
Kenji Okuda, Shun-yuan Yeh, Chon-in Wu, Keng-hao Chang, and Hao-hua Chu
National Taiwan University
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What is GETA?
a kind of the traditional Japanese sandals
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Outline
Motivation Related works Basic idea Design, implementation and evaluation
(three versions try and error)
Conclusion Current works
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Motivation Infrastructure cost (barriers for the user) (deployment, calibration, maintain)
Active Badge: IR receivers Active BAT: Ultrasonic receivers + RF Cricket: Ultrasonic beacons + RF RADAR: WiFi network Smart floor: pressure sensors
Goal Infrastructure free (not succeed so far in this paper-> low infrastructure) High accuracy
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Related Works
Lee et al. proposed a method by recognizing a sequence of incremental
motions. E.g. 5 steps north followed by 14 steps east.
Only can tell from place to place e.g. living room, bedroom
Point research provides a vehicle self-tracking system
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Basic idea of Foot-print Approach
( 0, 0 )
( 180, 200 )
Sp
S1
S2
S3
S4
S5
Sp=S1+S2+S3+S4+S5
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How to sum up those vectors mathematically
Coordinate system 1
Coordinate system 1’
(x1, y1)
(x2, y2)
(xc2, yc2)
(xc1, yc1)
θCoordinate system 2
Need coordinate transformation for each left foot step.
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Three try-and-error versions
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Design version I
Bottom view side view
Ultrasonic Transmitte
rs
Ultrasonic
Receivers
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Why using two transmitters
P1 (known)
P2 (Unknown)
T1d1
d2
d3
d4
Can be rotated!!
fixed
(fixed)
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Why using two transmitters
P1 (known)
P2 (determined)
T1
Can Not be rotated any
more !
T2
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Problems of Design I
Poor accuracy! The interference of the signals from two
transmitters. Measures the incorrect vectors Miss-detection of the user’s steps All the calculations become failure.
Can not distinguish the user is moving forward or backward!
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Design version II
Bottom view side view
Ultrasonic Transmitte
r
Ultrasonic
Receivers
Pressure sensor
Orientation Sensor
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Design II Performance Evaluation
0
2
4
6
8
10
0 100 200 300 400 500 600
distance (cm)
erro
r %
0.43(steps/sec)
0.7(steps/sec)
1.3(steps/sec)
0
10
20
30
40
50
0 100 200 300 400 500 600
distance(cm)
erro
r d
ista
nce
(cm
)
0.43(steps/sec)
0.7(steps/sec)
1.3(steps/sec)
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Two Main Error Sources
θerrP1 P2
Real path Calculated path Error Displacement
P2
Steps
Error
Real path Calculated path Error Displacement
P1
Fig1. Ultrasonic device err Fig2. Orientation sensor err
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The solution of design II
Passive RFID tag
Adds a RFID reader in the GETA and put some tags in the environment.
Real Path of the user Calculated Path of the user
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Design version III Orientation
SensorRFID Reader
Pressure Sensor
Ultrasonic Receivers board (with 2 Ultrasonic receivers)
Ultrasonic transmitter
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Hardware Sensors of Design III
Pressure sensors Phidgets
Ultrasonic device NAVINote (an electronic pen product) Resolution : 0.2 mm
Orientation sensor InterSense InterTrax2 Resolution : 0.02 degree
RFID Reader SkyeTek M1 Read range: ~5cm
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Design III Performance Evaluation
Doesn't step over thetag
Doesn't step over thetag
020406080
100120140
0 500 1000 1500 2000 2500 3000
distance (cm)
erro
r dis
tanc
e (c
m) one tag per 3 m
one tage per 5 m
The positioning error under different tag density over the walking distance.
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Conclusion
A interesting self tracking method. Low infrastructure cost. The error of the orientation dominants our
system accuracy. Still have some limitations
E.g. climbing the stairs, walking crossover..
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Current Works
Increase the accuracy
(reducing the orientation error) Solve the obstruction problem Going down/up stair problem Enhance the wearability (wireless)